EARTHQUAKE SIMULATOR TESTING OF ACOMBINED SLIDING BEARING AND RUBBER … · 2010. 3. 30. · 2.3a Change of hysteresis loop with axial load (30% shear strain) 13 2.3b Change of hysteresis

REPORT NO.

UCB/EERC-87/04

DECEMBER 1990

PS9Z-192lJb2

EARTHQUAKE ENGINEERING RESEARCH CENTER

EARTHQUAKE SIMULATOR TESTING OFACOMBINED SLIDING BEARING ANDRUBBER BEARING ISOLATION SYSTEM

by

JAMES M. KELLY

MICHEL S. CHALHOUB

Report to the National Science Foundation

COLLEGE OF ENGINEERING

UNIVERSITY OF CALIFORNIA AT BERKELEY

'lEPRODUCED B'

U.S DEPARTMENT OF COMMERCENATIONAL TECHNICAL INFORMATION SERVICESPRINGFIELD, IIA. 22161

For sa'" by fhe National TechnicollnfarmationService, U.S. Deportment of Commerce_Springfield, Virginio 24161

See bac~ of report for up to date listing ofEERC reports.

DISCLAIMERAny opinion., finding., and conclusions orrecommendation. expressed in this publica

tion are those of 'hI!' author. and do not neeeuarily rellect the views of fhe National Sci.ence Foundation or the Earthquoke Engineering Research Center, Universify of California

a' Ber~eley.

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'0277 ·101 -REPORT DOCUMENTATION II. RE"OIlT NO. I~

SoPB92-192962PAGE NSf!ENG-87049

.... Title and Subtitle !L IIleport 0.1•

Earthquakt! Simulator Testing of a Combined Sliding Bearing and Dect!mbt!r 1990Rubber Bearing Isolation System ..J. "'1It~o,h) .. .." ......"'1 O....Nul"'n ".pt. No.James M. Kt!lly and Michel s. Chalhoub UCB!EERC-87!04t. r.rfarm,n, O....nl..'ion N.ma .nd Add,.,. 10. l'rolec:tlT..../W.... U"', No.

Earthquake Engint!ering Research CenterLniversit~· of California. Berkeley n. Cont,ecUC) II' GrlntCGJ No.

1301 Suo 46th Street (C)

Richrno!1d. Calif. 94804 cCJECE-8414036

12. 500"'0"'''. O,.a",i,atloft N.m..... Add.... n. ',PI 01 ".1IOft &. Peri... e-.dNational Science Foundation1800 G Stret!t I N.W.Washington. D.C. 20550 1..

JIS. Supp~~m.l"IC.ry N~t•• !

III

I" "'bstract CUm,l: 2-10 __II

I- Essential requirements of a base isolation system include wind restraint. stability. and

Ifail-safe capacity., A new baSt! isolation system combining sliders and rubber bearingsinherently satisfies all three requirements. and possesses other advantages. The system wastested on the Earthquake Simulator at the University of California at Berkeley by installingit under the base of a one-fourth scale nine-story steel structure and subjecting it todifferent earthquake inputs. The base behaves as fixed for low magnitude inputs. Whensliding starts the rubber bearings provide additional stiffness and recentering. Under very .severe inputs the tension devices reach their locking limit and cause a large increase in thelstiffness of the system. Areas of base shear hysteresis loops are drastically enlarged bythe addition of sliders. Displacements are better controlled than the ones for a purelyelastomeric isolation system. Vertical deflections due to large horizontal drift encountered

- in solely rubber systems, are eliminated. The fail-safe capacity is provided by the tcnsion Irestrainers and by the constant contact of the sliders with the base. The sliders were also I

tested separately on a static rig. The friction coefficient for teflon-stainless steel 1

increases With sliding velocity and decreases with pressure. Teflon sustains high pressures Iwithout remarkable changes in its properties. The main aspect of its wearing is Idelamination.

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-

EARTHQUAKE SIMULATOR TESTING OF A COMBINED

SUDING BEARING AND RUBBER BEARING ISOLATION SYSTEM

by

James M. Kelly

and

Michel S. Chalhoub

Report to the National Science Foundation

Repon No. UCB/EERC-87/04Earthquake Engineering Research Center

College of EngineeringUniversity of California at Berkeley

December 1990

ABSTRACT

Essential requirements of a base isolation system include wind restraint, stability, and fail

safe capacity. A new base isolation system combining sliders and rubber bearings inherently

satisfies all three requirements. and possesses other advantages. The "ystem was tested on the

Earthquake Simulator at the University of California at Berkeley by installing it under the base

of a one-fourth scale nine-story steel structure and subjecting it to different earthquake inputs.

The base behaves as fixed for low magnitude inputs. When sliding starts the rubber bearings

provide additional stiffness and recentering. Under very severe inputs the tension devices reach

their locking limit and cause a large increase in the stiffness of the system. Areas of base shear

hysteresis loops are drastically enlarged by the addition of sliders. Displacements are better con

trolled than the ones for a purely elastomeric isolation system. Vertical deflections due to large

horizontal drift encountered in solely rubber systems, are eliminated. The fail-safe capacity is

provided by the tension restrainers and by the constant contact of the sliders with the base. The

sliders were also tested separately on a static rig. The frj.;tion coefficient for tefton-stainless

steel increases with sliding velocity and decreases with pressure. Teflon sustains high pressures

without remarkable changes in its properties. The main aspect of its wearing is delamination.

· ii .

ACKNOWLEDGEMENTS

The research reported here was supported by the National Science Foundation under Grant

No. ECE·8414036 and was carried out at the Earthquake Simulator Laboratory of the

Earthquake Engineering Research Center of the University of California at Berkeley. The authors

would like to thank the National Science Foundation for its support, especially Dr. A. J.

Eggenberger.

The isolation bearings used in the experimental work were provided to the project by Oil

States Industries, Athens. Texas (now Bearing Pad Division of Fluorocarbon Inc.) and by thl:

Malaysian Rubber Producers' Research Association, Hertford, England.

- iii -

TABLE OF CO~TENTS

ABSTRACT .

ACKSOWLEDGEMESTS ii

TABLE OF CO:\TE:\TS iii

LIST OF TABLES v

LIST OF FIGlJRES vi

I. TEFLOX AXD RUBBER FOR BASE ISOLATIOS ..

11. TEST STRUCTl;RE ASD ISOLATION SYSTEM 3

1. Test Structure 3

2. Mass Distribution 4

3. Elastomeric Bearings.. '" 4

4. Uplift Restrainers 6

5. Sliding Bearings 7

6. The Combined Isolation System 8

(1) Providing Threshold for Base Motion 8

(2) Additional Stiffness and Restoring Effect 8

(3) Control of Drift and Overturning 9

7. Tables and Figures 10

111. TEST FACILITIES 20

1. Earthquake Simulator 20

2. Input Signals 20

3. Data Acquisition System 21

IV. INSTRUMENTATION 22

1. Accelerations , 22

2. Displacements 22

3. Forces 23


• iv •

V. TEST PROGRAM 34

1. Table Motions 34

2. Test Sequence 35


VI. STATIC TESTS FOR SLIDISG BEARlSGS 58

1. General 58

2. Test Machine and Data Acquisition 59

3. Test Sequence 60

4. Test Results 6]


VII. EARTHQUAKE SIMUlATOR TEST RESULTS 89

1. General.............................................. 89

2. Displacement\> 90

3. Accelerations 91

4. Effect of Input Magnitude 93

5. Base Shear 94

6. Energy Dissipation Efficiency............ 95


VIII. COMPARISOS OF EARTHQl:AKE SIMUlATOR TEST

RESULTS WITH SEAOSC TE~"ATIVECODE 144

1. General.................... 144

2. Displacements 144

3. Base Shear 147

4. Lateral Force Distribution ]47

5. Comparison with Response Spectra Analysis 148

6. Future Research and Conclusions )49

7. Tables and Figures ]5]

IX. CONCLUSIONS ] 61

REFERENCES 164

Table

T-2.1

T-2.2

T-4.1

T-5.1

T-6.1

T-6.2

T-6.3

T-7.1

T-7.2

T-7.3

T-7.4

T-7.5

T-7.6

T-8.1

T-8.2

T-8.3

T-8.4

• v •

LIST OF TABLES

Pa.

Scale factors. 10

MRPRA SET #1 bearings - static rig tests. Change in effective stiffness

with axial load and horizontal shear strain. 10

Channel list for base isolated structure. 25

Test program: listing of test runs. 38

List of channels for triangular signal rig testing. 64

Sliders test sequence for triangular signal. 65

Variation of friction coefficient for 4x4 inch teflon-stainless steel sliders

with pressure and sliding velocity. 67

Peak values of base lmd ninth story response (top), with their corresponding

amplification ratios (bottom). 97

Base displacement end-of-signal offsets for eight eanhquake records with their

corresponding peak table displacement and peak table acceleration. 98

Acceleration amplification ratios at fourth and ninth stories for fixed base and

hase isolated structure. 98

Peak values of base and ninth story response (top), with their corresponding

amplification ratios (bottom), for EI Centro record with increasing span. 99

Energy dis.<;ipation efficiency of the combined rubber-sliders isolation system. 100

Equivalent damping and equivalent stiff..ess obtained from experimental

hysteresis loops of base shear for eight records. ~q around 20%. 100

EPA and EPV values with the corresponding codt displacements for

the eight records used. 151

Comparison of code displacement with test displacement showing overestimation

for high frequency inputs and underestimation for low frequency inputs. 151

Measured base displacement, average spectral displacement, and average

spectral acceleration over 0.29 sec < T < 1.4 sec. 152

Maximum base shear from code formula. test, and response spectra analysis. 152

- vi •

LIST OF FIGURES

Figure Pap

2.1 Nine story steel frame showing dimensions and mass distribution 112.2 MRPRA SET _1 bearing showing dimensions 12

2.3a Change of hysteresis loop with axial load (30% shear strain) 13

2.3b Change of hysteresis loop with axial load (60% shear strain) 132.3c Change of hysteresis loop with axial load (100% shear strain) 14

2.4 Chmge in effective stiffness with axial load and ilil..:lil strain 1425 Natural rubber bearing showing details 15

2.6 Modification of central hole to acc.omrnodate tension device 15

2.7 Tension restraint showing dimensions 16

2.8 Effect of tension device on horizontal stiffness 17

2.9 Teflon-stainless steel slider showing dimensions 18

2.10 Disposition of tension controlled bearing under corner column and teflon-stainless

steel slider under adjacent interior column. repeated 4 times for the entire model............. 19

4.1 Location and channd numbers of accelerometers on base isolated structure 27

4.2 Location and channel numbers of potentiometers on base isolated structure 27

4.3 Location and channel numbers of DCDTs on base isolated structure 284.4 Location and channel numbers of load cells under base isolated structure 29

4.5 Location and channel numbers of accelerometers on fixed base structure 30

4.6 Location and channel numbers of potentiometers on fixed ba.~ structure 30

4.7 Transversal (north) frame of the structure showing horizontal accelerometers 31

4.8 North-east comer: rubber bearing on load cells, potentiometer measuring total

vertical deformation, accelerometer measuring vertical base acceleration 31

4.9 Side view of north rubber bearings 32

4.10 Three channels of a comer load cell measuring axial, shear, and bending forces 324.11 South-cast comer: DeDTs mea~uring total (bottom DCD1) and column

(top DCD1) vertical defonnations 33

5.la EI Centro 1940 sOOe, span=375. PTA=0.73 g 42

5.lb Response spectra. El Centro 1940 sOOe, span=375, PTA=0.73 g 43

5.2a Mexico City 19R5 s6Oe. span.375, PTA=O.IS g 44

5.2b Response spectr,. Mexico City 1985 s6Oe, span=37S, PTA=0.18g 45S.3a Bucharest 1977 sOOe, span=300. PTA=0.27 g 46

5.3b Response spectra. Bucharest 1977 sOOe, span=300, PTA"'O.27 g........................................... 47

5.4a Miyagi·Ken.Oki 1978 wOOs, span=350. PTA=O.33 g 48

5.4b Response spectra. Miyagi-Ken-Qki 1978 wOOs. spana 350, PTA-O.33 g............................ 49

Figure

5.5a

5.51:15.6a

5.6b

5.7a

5.7b

5.8a

5.8b

• vii -

Pap

Pacoima Dam 1971 sl6e. span=350. PTA=O.49 g 50

Response spectra. Pacoima Dam 1971 sl6e. span=350. PTA=0.49 g 51

Parkfield 1966 n65e. span=350. PTA=0.41 g.............................................................................. 52

Response spectra. Parkfield 1966 n65e, span=350. PTA=0.41 g 53San Francisco 1957 s8Oe. span=200. PTA=1.20 g 54

Response spectra. San Francisco 1957 sBOe. span=200. PTA=1.20 g 55

Taft 1952 s6ge. span=350. PTA=O.72 g 56

Response spectra. Taft 1952 s6ge. span=350. PTA=O.72 g 57

6.1 Rig used for slider tests 68

6.2 The thr~e basic components: rubber bearing, tetlon. stainless steel plate 69

6.3 Slider as mounted on the static rig 69

6.4 Slider on load cell .,............................................................................................................................ 70

6.5 Data acquisition and control system for static rig testing 71

6.6 Tefton slider after repeated testing (250 cycles) 72

6.7 Tetlon wearing by delamination 72

6.8 Displacement. shear, and hysteresis loop for 4x4 inch slider,

v=O.1 in/sec. p=900 psi 73

6.9 Displacement. shear, and hysteresis loop for 4x4 inch slider.

v=5.0 in/sec, p=900 psi 74

6.10 Displacement. shear. and hysteresis loop for 4x4 inch slider.

v=15.0 in/sec. p=900 psi 75

6.11 Displacement. shear. and hysteresis loop for 4x4 inch slider.


6.12 Displacement, shear. and hysteresis loop for 4x4 inch slider.

v=5.0 in/sec. p=1200 psi 77

6.13 Displacement. shear, and hysteresis loop for 4x4 inch slider.

v=15.0 inlsec. p=1200 psi 78




v=5.0 in/sec. p=2000 psi 80

6.16 Displacement. sht:ar. and hysteresis loop for 4x4 inch slider.

v=15.0 inlsec. p=2000 psi 81

6.17 Displacement, shear, and hysteresis loop for 4x4 inch slider.

v=O.1 inlsec, p=2.500 psi 82

6.18 Displacement. shear. and hysteresis loop for 4x4 inch slider,

v=5.0 inlsec, p=2500 psi 83

6.19 Displacement. shear. and hysteresis loop for 4,,4 inch slider.

v=15.0 in/sec. p=2500 psi 84

Figure6.20

6.21

6.22

6.23

- viii -

PigeDisplacement, shear, and hysteresis loop for 4x4 inch slider,

v=O.1 in/sec, p=3000 psi .. 85

Displacement, shear, and hysteresis loop for 4x4 inl,;h ,>,ider,

v=5.0 in/sec, p=3000 psi 86

Displacement, shear, and hysteresis loop for 4x4 inch slider,

v=15.0 in/sec, p=3000 psi 87

Variation of friction coefficient with velocity and pressure 88

7.1 Acceleration Fourier transforms for EI Centro record span 200 101

7.2 Acceleration Fourier transforms for Bucharest record span 250 10:?

7.3 Acceleration Fourier transforms for Mexico City record span 50 (left)

and span 150 (right) 103

7.4 Base shear hysteresis loop for EI Centro record span 200 104

7.5 Base shear hysteresis loop for Bucharest record span 250 105

7.6 Base shear hysteresis loop for Mexico City record span 50 (left) and 150 (right) 106

7.7 Deflected shape of structure on rubber-sliders system, at maximum story

displacements for EI Centro signal 375 span 107

7.8 Deflected shape of structure on ru~ber-sliders system, at maximum

story displacements for Mexico City signal 375 span 108

7.9 Deflected shape of structure on rubber-sliders system, at maximum

story displacements for Bucharest signal 300 span 109


story displacements for Miyagi-Ken-Oki signal 350 "pan 110


story displacements for Pacoima Dam signal 350 span III


story displacements for Parkfield signal 350 span 112


story displacements for San Francisco signal 200 span 113


story displacements for Taft signal 350 span 114

7.15 Story drift time history for San Francisco record at 100 horizontal

span (PTA=0.7g, left) and 200 horizontal span (PTA=1.2g. right) 115

7.16 Top figure showing base drift final offset, El Centro 375 base offset=-0.06 in.

(left), Mexico City 375 base offset=0.21 in. (right) 116

7.17 Top figure showing base drift final offset. Bucharest 300 base offset=-o.OO6 in.(left), Miyagi-Ken-Oki 350 base offset=0.19 in. (right) 117

7.18 Top figure showing base drift final offset, Pacoima Dam 350 base offset=-o.025 in.

(left), Parkfield 350 base offset=-o.041 in. (right) 118

7.19 Top figure showing base drift final offset, San Francisco 200 base offset=0.037 in.(left), Taft 350 base offset=0.057 in. (right) 119

- IX -

~n ~

7.20 Acceleration Time histories normalized to peak table acceleration for

EI Centro record 125 horizontal span (pTA=0.25g, left)and 375 horizontal span (pTA=0.73g, right) 120

7.21 Acceleration time histories normalized to peak table acceleration for

Mexico City record 100 horizontal span (PTA=O.06g, left)and 375 horizontal span (pTA=0.18g, right) 121


Bucharest record 175 horizontal span (PTA=O.17g, left)

and 300 horizontal span (pTA=0.27g. right) 1227.23 Acceleration time histories normalized to peak table acceleration for

Miyagi-Ken-Oki record 150 horizontal span (PTA=O.16g, left)

and 350 horizontal span (PTA=0.33g, right) 1237.24 Acceleration time histories normalized to peak table acceleration for

Pacoima Dam record 125 horizontal span (pTA=0.18g. left)

and 350 horizontal span (pTA=0.49g. right) .. 124


Parkfield record 125 horizontal span (PTA=0.14g, left)and 350 horizontal span (pTA=O.41g, right) 125

7.26 Acceleration time histories normalized to peak table acceleration forSan Francisco record 100 horizontal span (pTA=O.73g, left)and 200 horizontal span (pTA=120g, right) 126

7.27 At::celeration time histories normalized to peak table acceleration for

Taft record 100 horizontal span (PTA=O.20g, left)and 350 horizontal span (pTA=O.71g, right) 127

7.28 Acceleration amplification ratios along elevation of fixed base structure for

Bucharest (PTA=O.l7g), Miyagi-Ken-Oki (pTA=0.16g), Pacoima (PTA=O.18g),

Parkfield (pTA=0.14g). San Francisco (PTA=O.73g).

and Taft (PTA=O.20g), input motions 128

7.29 Acceleration amplification ratios along elevation of base isolated structure on

r'lhber-sliders system for Bucharest (pTA=0.25g), Miyagi-Ken-Oki (PTA=0.33g),

Pacoima (PTA=0.49g), Parkfield (pTA=0.41g). San Francisco (PTA=l.20g),and Taft (PTA=O.72g), input motions 129

7.30 Performance of the rubber bearing slider bearing combined system withincreasing input magnitude, under "4 time scaled EJ Centro record

between 150 and 425 horizontal span 130

7.31 North-west (left) and north-east (right) rubber bearings hysteresis loops under

EI Centro 150. 300. and 400 horizontal span showing stiffeningdue to tension device 131

7.32 Base shear hysteresis loop at isolation interface for EJ Centro 375 horizontal span

(PTA=O.73g, left) and Mexico City 375 horizontal span (pTA=O.l8g. right) 132

Figure

7.33

7.34

7.35

7.36

7.37

7.38

7,39

7.40

7.41

7.42

7.43

8.1

8.2

8.3

8.4

8.5

8.6

8.7

8.8

• x -

Page

Base shear hysteresis loop at isolation interface for Bucharest 300 horizontal span

(PTA=0.27g, left) and Miyagi-Ken-Oki 350 horizontal span (PTA::0.33g. right) 133

Base shear hysteresis loop at isolation interface for Pacoima Dam 350 horizontal

span (PTA=0,49g, left) and Parkfield 350 horizontal span (pTA=0.41g, right) 134

Base shear hysteresis loop at isolation interface for San Francisco 200 horizontal

span (PTA=1.20g, left) and Taft 350 horizontal span (PTA=O.71g, right) 135

Energy dissipation at isolation interface for ';4 time scaled EI Centro record

at 375 horizontal span (PTA=0.73g) 136

Energy dissipation at isolation interface for v'4 time scaled Mexico City record

at 375 horizontal span (PTA=O.18g) 137

Energy dissipation at isolation interface for v'4 time scaled Bucharest record


Energy dissipation at isolation interface for ';4 time scaled Miyagi-Ken-Oki record

at 350 horizontal span (PTA=0,33g) 139

Energy dissipation at isolation interface for v4 time scaled Pacoima Dam record

at 350 horizontal span (pTA=O.49g) 140

Energy dissipation at isolation interface for ';4 time scaled Parkfield record


Energy dissipation at isolation interface for ';4 time scaled San Francisco record

at 200 horizontal span (PTA=l.20g) 142

Energy dissipation at isolation interface for v'4 time scaled Taft record


Story shear envelope from test, code f<.rmula. and response spectra analysis

Table input: .[4 time scaled EI Centro, horizontal span 375, PTA=0.73 g 153

Story shear envelope from test. code formula, and response spectra analysis.

Table input: ';4 time scaled Mexico City, horizontal span 375, PTA=0.18 g 154

Story shear envelope from test, code formula, and response spectra analysis.

Tllble input: v'4 time scaled Bucharest, horizontal span 300, PTA=O.27 g 155


Table input: .f4 time scaled Miyagi-Ken-Oki, horizontal span 350, PTA=0.33 g 156


Table input: ';4 time scaled Pacoima Dam, horizontal span 350, PTA=0,49 g 157


Table input: ';4 time scaled Parkfield, horizontal span 350, PTA=0.41 g............................. 158


Table input: ';4 time scaled San Francisco, horizontal span 200, PTA=1.20 g 159


Table input: .[4 time scaled Taft, horizontal span 350. PTA=O.72 g 160

CHAPTER ON E

TEFLO~ AND RUBBER FOR BASE ISOLATION

Base isolation is a seismic design strategy based on the concept that a structure can be partially

protected from earthquakes hy uncoupling it hom the ground. This cun be achieved by mounting the

structure on horizontally flcxihle foundations capable of accommodating relatively large displacements

and thus acting as shock ahsorbers. The debate among engineers whether to attach a structure rigidly

to the ground or to let it move at very low frequency has existed since 1909 (1J. The more

conventional method has almost always been chosen.

Base isolation is rapidly gaining acceptance, however, and many systems have been proposed in

recent years. The buildings which have been constructed ''\'Urld-wide using the concept have in the

main been built using laminated elastomeric bearings of natural or artificial rubber, often with

additional clements for thc purpose of enhanced energy dissipation and control of displacements under

wind loading [2, 3. 4). A three-story school in Lambesc ncar Marseilles, France. consisting of three

buildings separated by seismic gaps, uses 152 multilayered c1astomeric isolall'rs [5J. The isolators are

12 inch diameter circular pads containing 20 layers of ruhher for a total rubber thickness of 1.6 inches.

A government office building in Wellington. New Zealand, is built on laminated natural rubber

bearings with cylindrical lead plugs pressed in a central hole. The effect of the lead is to increase the

damping and to provide displacement control. In South Africa, a nuclear power plant rests on an

isolation system using neoprene bearings with bronze-stainless steel sliders installed on top of the

bearings, designed by a French construction company [6]. When the neoprene bearings can no longer

accept the increasing horizontal displacement. sliding starts. Interest in base isolation is extremely high

in Japan. and there are now several buildings in that country on isolation systems, mostly of the

elastomeric bearing type with additional damping clements.

In the United States, the first building using laminated elastomcric pads for seismic protection is

the Foothill Communities Law and Justice Center in Rancho Cucamonga [7J. It was dedicated on 20

March 1986. In Salt Lake City, the City and County building is in the process of being rehabilitated by

the insertion of elastomeric isolators between its base and the ground [8J. Base isolation seems to be

-2-

the best solution for the rehabilitation of old buildings that contain procious architectural detailing.

There are several important requirements for hase isolation systems. They have to provide a low

frequency motion with relatively high damping in order to limit the displacements to an acceptable

value. The system must incorporate a wind restraint and have a recentering effect. In the case of an

unexpectedly severe earthquake. the system must provide a fail-safe capacity.

Sliding systems have been proposed as aseismic isolation systems because of their inherent

simplicity and their relatively low cost. However, they present problems such as excessive drift and

lack of fail-safe constraints. This is mainly due to thdr force-deflection characteristics which show no

resistan" once the sliding threshold is overcome. In addition, they may produce a very low effoctive

frequency, because of the magnitude of the input, leading to extremely large relative displacements.

The arrangement tested in the present research combines sliders with elastomeric springs, and

thereby produces a system with the desirable features of a base isolation system and none of the

disadvantages of a purely sliding system. The damping needed in a base isolation system is here

provided by friction energy dissipation. The high energy dissipation capacity of the system. shown by

the large area of its hysteresis loops, is caused by the addition of the sliders.

Sliding bearings are used in large reinforced concrete structures to control shrinkage cracking and

thermal deformations, but in that application, they include a mechanism that locks up the building at

one end, so that the sliding clements play no role in the seismic response of the structure. The present

system replaces the lock-up mechanism by flexihle ruhher hearings arranged around the periphery of

the building, and incorporates the sliding clements into the seismic response.

Since this system is but a slight modification of an existing practice. it i'i possible that resistance

to the usc of such a system by civil engineers will he less than that which has been shown against the

rubber bearing isolation system which is a more radical departure from conventional engi!leering.

-3-

CHAPTER TWO

TEST STRUCTURE AND ISOLATION SYSTEM

1. Test Structure

A one-fourth scale, nine-story steel frame was used in this experiment. The structure comprised

four one-bay frames in the transverse direction and two three-bay frames in the longitudinal direction.

An eccentric K-bracing system was placed in both directions. In the middle bays of the longitudinal

frames, the hraces had an eccentricitv of 6 inches and consisted of double angles 1 1 )( 1 1 )( 1 inch at.. 2 2 4

the first and fifth to ninth Hoors, and consisted of double angles 1)( 1 )( ~ inch at the second, third and

fourth floors. On the two exterior transversal frames, the braces had an eccentricity of 16 inches and

consisted of double angles 1 1 xli x 1 inch for the upper seven stories and double angles 2 x 2 x 32 2 ~ M

inch for the lower two stories. For the girders, single angles 3 x 3 ~ x ~ inch were used to make an

X-shaped brace system. The floors were about 3 feet high each, except for the first floor which was 4

feet high. The structure and its dimensions arc shuwn in Figure 2.1, and the scale factors are tabulated

in Table T-2.1.

As a rule of thumb, the fundamental period of a structure in seconds is close to one tenth of its

number of stories. There is no risk of resonance between the fundamental frequency of a stiff building

and that of the isolation system. For this reason, base isolation is well suited to low-rise buildings.

The center of gravity of a short building is relatively low and, thus, so is its overturning moment, so

that the clastomeric pads on which a base-isolated structure rests would always be in compression.

Very tall buildings of more than 20 stories have a fund"mental period above 2 seconds, and therefore

do not need to be base isolated. Hence, there is a critical category of medium-size structures between

9 and 20 stories, for which isolation can be effective but for which uplift can play a role in the

performance of the isolation system. The structure simulated in the present experiment falls into this

category. Its fixed base fundamental frequency was 3.4 Hz, corresponding to 1.7 Hz in the prototype,

For this rcason, it was well suited to examine the possibility of extending the concept of base isolation

further for medium rise buildings.

-4-

2. Mass Distribution

In order to introduce the desired inertia forces and overturning moment, concrete slabs were

allached to the frame girders. The distribution of the concrete weights was limited by the shaking

tahle load cap<icity of about 130 kips and its overturning moment capacity of about 1,100 kip-ft. The

mass distrillution is shown in Figure 2.1. The weight of the structure was about one kip per story, and

after addition of the concrete slabs, the weight was distributed in a pattern of

i - '} - 9 - 9 - 9 - 13 - 9 - 9 - 9.2 - 14 kips, from top to honom, leading to a total of about 91 kips for

the entire model. At the fourth floor, a slightly higher mass was provided to increase the overturning

moment effect in the response. The large mass <it the base simulates the boltom slab of a real building

which is generally heavy and rigid in order to distribute the vertical loads transmitted from the upper

stories to the foundations uniformly.

3. Elastomeric Bearings

The idea of base isolation was proposed many years ago. However, it did not become practical

until recent developments in the use of elastomers.

Rubber-like materiaLs ha\'e been widely used in engineering applications, for purposes other than

earthquake protection of buildings. Elastomeric blocks have been installed under bridge decks to

accommodate slow differential movements; they have found application in the isolation of buildings

against high frequency vibrations caused by traffic and they have also heen used as clastic foundations

for madinery and motors.

For the seismic protection of structures, c\astomeric bearings have to fulfill different conditions. It

is commonly accepted that vertical components of earthquake motion are much less severe in their

effects than horizontal ones. Damage to a structure is mainly due to amplification in the horizontal

direction. For this reason, seismic isolation uses elastomeric bearings that are very stiff in the vertical

direction, but can accommodate large horizontal deflections. Large venical stiffness avoids the

amplification of rocking motion. Large horizontal flexibility causes the building to behave roughly as a

single degree of freedom oscillator in the horizontal direction. lIS motion will have a very low

-5-

frcqucn~y be~ause of the large mass and tne low stiffness. By careful design of the bearings in

relation to the mass of the building, this frequency can be hrought to a value low enough to be outside

the range of frequency content of earthquake excitation.

The pads used in this experiment were multilayered c1astomcric bearings made of thin rubber

layers interleaved by thin steel plates. In the fabrication process, the rubber and steel arc bonded

together under high temperature and high pressure. The effect of the bond is a suhstantial increase in

the compression modulus [9, 10), which prevents (he rubber from bulging when subjected to a vertical

load.

For the same mass distribution on the model, yielding 91 kips of total weight, CWo isolation

systems using elaslomeric hearings were used. A previous isolation system consisted of a set of eight

filled rubber hearings provided by the Malaysian Ruhber Producers' Research Association (MRPRA set

#1), Hertford, England. Then steel-teflon sliders were used under the four intemal columns of the

structure and four natural ru"ber bearings with cylindrical central holes were installed under the

corners. The central holes were initially designed to lodge a lead plug in each bearing to increase its

stiffness and damping and thus provide better displacement control. In their present use, however,

tension devices were installed in the holes instead of the lead plugs.

?roperties of the Elastomeric Bearings

The MRPRA set #1 hearings had a 5.75)(5.75 inch square cross section and consisted of 16

layers of ruhber each 0.21 inch thick, yielding a total height of rubber of 3.4 inches, interleaved by 15

steel shims each 0.06 inch thick. The two extreme plates at the top and bottom of the bearing were

each 5/8 inch thick. A 1/16 inch thick protective layer of rubber was glued on their lateral areas

(Figure 2.2). These arc used in real construction for the protection of the elastomer against external

factors such as fire and oil. Their measured vertical stiffness was around 420 k/in. at 1.6% vertical

strain and their horizontal stiffness around 1.1 k/in. at 60% shear strain. The shear modulus of the

elastomer was 100 psi.

-6-

The natural rubber bearings used with the sliders had a 5.75x5.75 inch square cross section and

consisted of 6 layers of rubber 3/8 inch thick cach inccrlcaved by 5 steel shims each 0.2 inch thick.

Thc t{lp and bottom limiting plates were 1 inch thick. The bearings had Ii 1.25 inch diameter central

hole. A 1'~ inch thick protective rubber layer was glued to their lateral surface (Figures 2.5 and 2.6).

Their horizontal stiffness was about 1.3 klin. at 50% shear strain. Elastomeric bearings do not have a

linear force-deflection relationship and the non-linearity increases with the level of strain and the

applied axial load. For practical purposes, however, a linear relationship can be satisfactorily used.

When installed under the structural model, each of the external bearings carried 9 kips while each of

the internal ones carried ahout 14 kips.

Results ohtained from static rig tests for the c1astomeric bearings at different axial loads and

different shear strain levels, are tahulated in Table T-2.2 and plotted in Figures 2.3 and 2.4. It is

noticed that the effective stiffness drops with amplitude of excitation and with axial load. The amount

of damping in the bearings was also determined to he around 5% for both types. Typical hysteresis

loops for MRPRA set #1 bearings and for the comhined system while tested under the model are

shown in a later section.

4. l:plift Restrainers

The taller a structure is, the larger is its overturning moment, and the greater is the risk of

inducing tension in its foundations. Since excessive tension could be destructive for multilayered

ruhher hearings, a deVice was installed inside each of the outer corner hearings. The role of the device

was to control uplift and horizontal drift. The restrainer consisted of a short steel siee,.: and two steel

holts. The bohs were connected to the two limiting plates of the hearing. The assemblage locks when

the holts ar..: pulled a certain distance aparl. Its tension capacity was about 18 kips. The horizontal

displacement of the bearing at which the restrainer locks can be adjusted by appropriate tightening of

the bolts. The bc~avior of the bearing is influenced by the presence of the tension devices only when

the deflection is large. At the level of horizontal displacement corresponding to the locking of the

restrainers, the stiffness of the unit increases substantially. A tension device with its dimensions is

·7-

shown in Figure 2.7. A typical hysteresis loop for a natural rubber bearing equipped with a tension

device is shown in Figure 2.8.

It should be noted that the restrainer system docs not act as a sudden stop. Although the

restrainer is effectively rigid when it acts, the bearing can continue to displace horizontally by

shortening vertically, thus the normally low horizontal stiffness is replaced by a stiffness that is related

to the much higher vertical stiffness.

S. Sliding Bearings

The basic components of a slider consisted of a tefton layer bearing against a stainless steel plate,

sec Figure 2.9. The teflon layer had a thickness of about 1125 inch, backed by a 112 inch thick layer

of Fabreeka" pad bonded to a 118 inch thick steel plate. This component was mounted on a rubber

bearing constrained against horizontal movement. The stainless steel component consisted of a 1/32

inch thick stainless steel mirror, point welded ((J a 1/8 inch thick steel plate. Their areas were 10x7

and 1O.5x7.5 square inches, respectively.

The coefficient of friction for the teflon-steel units, as provided by the manufacturer, was about

5%, however, a separate testing of the sliders showed a higher coefficient of friction, namely around

17%. This caused concern about the isolation effectiveness that would be provided by sliders of such

a high coefficient of friction, since the threshold of the base shear at which the sliding would start was

correspondingly increased. For this reason, after the structure was tested with the system described

above, the area of the teflon was reduced from 6 x 6 to 4 x 4 square inches. This was done since the

coefficient of friction of the teflon with other surfaces decreases with increased pressure in the material.

When the area was reduced to 4 x 4. the coefficient of friction dropped to about 12%. The reason for

the discrepancy between the specified and measured coefficients of friction was mainly the effect of the

sliding .elociry and the pressure in the material.

The amplitude of travel of the teflon on the steel before it reaches the edge of the plate, was 3

inches for the 4)( 4 sliders and 2 inches for the 6 Ie 6 .

-8-

6. The Combined Isolation System

In general, an isolation system consists of a group of devices mounted together in order to

decouple the building from the ground motiol1. The present system using a combination of elastomeric

bearings, sliders. and uplift restrainers (Figure 2.10). was designed to fulfill three important goals:

(1) Providing Threshold for Base Motion. The friction of the sliders keeps the structure from

moving under wind loading and small earthquakes. The base shear must exceed a certain limit

in order to start sliding. This limit is proportional to the friction coefficient, and to the fraction

of the weight of the model carried by Ull~ sliders. This wind restraint capacity was

experimentally verified by applying earthquake signals of very small spans. Figure 7.6 shows the

base shear hysteresis loops for the Mexico City eanhquake input at a horizontal span of 150;

very little relative motion was recorded for this level of excitation. By examining the Fourier

transfonns of the corresponding floor accelerations (Figure 7.J). it was noticed that they were

similar to the ones for the fixed base case. The ability of an isolation system to ensure a certain

fixity for low level dynamic loading renders it practical and avoids unnecessary movement of the

structure when seismic isolation is not yet needed.

(2) Additional Stilfne65 and Restoring Effect. Once the shear force that activates the sliders is

reached, their horizontal stiffness drops from a very large value to zero, causing an unrestrained

displacement. For this reason. sliders were combined with elastomeric bearings that would

provide an additional stiffness. The force-deflection relationship of the combined system would

be theoretically bilinear with infinite initial stiffness, followed by a finite stiffness provided by

the rubber bearings, which are kept free to deflect horizontally. instead of the zero stiffness that

would otherwise characterize the sliders. This arrangement also ensures a restoring force that

will bring the structure to almost its original at rest location. A series of experiments performed

on a rigid block to study its sliding response under eanhquake signals is described in reference

[11]. The large displa~ment offset that remains at the cnd of the signal shows the need for a

restoring spring. For the combined system. the base relative displacement time series under

different eanhquakes are shown in Figures 7.16 through 7.19. It is noticed that the offset is

-9-

reduced to a practically negligible value.

(3) Control or Drift and Overturnilll' The presence of tension devices inside the bearings, limits

the horizontal drift of the base and the uplift of the columns. If a medium-rise building were to

be base isolated. it would be essential to control its uplift; tension devices would prevent

C2. : strophical overturning in the case of an unexpectedly severe earthquake. Also, they provide

stiffening as they come close to locking: this compensates for the softening of the rubber

bearings.

It is also worthwhile mentioning the inherent fail-safe capacity that the present system possesses. The

horizontal stiffness of rubber bearings decreases with shear strain and axial load, and at a certain level

of axial load they become unstable. For this reason systems consisting of solely rubber bearings use

other accessories to provide fail-safe action on which the structure can depend in case of braring

buckling or bearing roll out. For the combined rubber-sliders system this problem is solved by having

the structure constantly resting on the sliders and when the base drift is very large some of the axial

load that was initially carried by the rubber bearings L.. transferred to the sliders.

The system. by combining sliders. elastomeric bearings, and tension devices, provides all the

functions needed for the seismic protection of a structure.

-10-

Table T-2.1 Scale factors.

PARA.\1ETER 1. seal.. modrl4 prolotll7"

LE;";CTH L I4

TIME .;r; I2

MASS L: I16

DISPLACE~E~T L I4

ACCELERATION III

STRESS I II

STRAl~ I II

FORCE L~I

16

AREA L~I

16

Table T·2.2 MRPRA SET '1 bearings. static rig tests.Change In ell'ective still'ness with axial load and horizontal shear stnln.

. MRPRA SET # 1 BEARINGS - EFFECTIVl:. STIFFNESS

- 301'>,6 sht>ar strain 60% shear strain 100% shear strain

AXIAL LOAD (k.) K.11 (k in I) K./ I (k.in· l) K./I (Ic.1n I)

5 I.4R 1.11 .10 1.44 1.08 0.91

20 1.30 0.96 0.77

30 1.15 0.8·' 0.62

40 1.00 0.69 0.42

45 0.95 0.64 -50 0.95 0.54 -60 O.R;) - .

Flpre 2.1

N

-11-

6'-6" 5'-0" 6'-6"i~-t-..:..--t---:......:..---t

I wr .....~======u:=::;::::;;;;::::::t4=======~--f-

b.'"If'

Nine story Iteel franae IIbowiDa ell........ ad ...... dlatributio••

-12-

L 1.75" Ir-~~-·

PLAN

o o

o~........ a_.9_5_" ~

SECTION"' ICIDCII

:Cl-......0.625" .teel plate ...... .....,

(top and bottom~",U 1.0-

-1- 1 II1U

0.21" rubber

... •1.0.,;

0.06" .teel .him

" r..

n nI I

FillUre 2.2 MRPRA SET'I .arilll sbowinl dimeDsioDs.

-13-

MRPPA II 1 RIG TESTSOWX:;E IN HYSTERESIS LOOP WInl AXIAL LOllD

1 INCH AMPLITUDE

r-SK

FoRCE

K1ps

-I

1.S0.0-0.5-1.0

-2 a::... -..JL.- ...l- ..L.- -1 ...L.- ~

-1.5

Figure 2.3a

01 SPI.J\CEMEm' INotES

Change of bysteresis loop with axial load (30% shear strain)_

2 I NCH AMPLITUDE

p. 5 K

FC,RCE

IeIPS -1

1o-2

-31::.. -1. ..1- -1. ..1- -1. -2

oJ

Figure %.3b

DISPLACfJoI.ENr %NCHtS

Chaap of bysterall loop with uialload ("" lbear straiD).

-14-

MRPRA "1 RIC n:STSCltl.NCE IN HYSTI:RESIS LOO? WI m AXIAL LOAD

3.5 INCH NiP!.l WDE

41=""-----------------r-----------------,

eORC£

l(

IpS

-I

p. 10 K

P - ~O r.P - 30 KP - 40 I(

---"..'

."..'

"

..~

4

... I%:- --I -!- ....L- -"

...

Figure Z.3t

DIS?I.ACEMENT INCiIES

Change of hysteresis loop with axial load (100% shear strain).

·15·

eentral hole 41=1.25"

dowel holl' 4>=5/8"

6"

,I

-0-I

-~-I

-0-I

1c ICl

PLAN

3.5" .J SECTION

m

ayer\q I I III II !· 3/8" rubber I

I

Vf1'

1/8" .teel.hi

.v-.II I :I • I Iq I• III · •

&-c.::

~~

Qt. t-~

~C'I

:

_1;;.:/:....;8;,.."~~~~ -=-O.:.:.1.=O_" ,~

Figure 1.5 Natural robber bearing showing details.

Flaure 1.6 Modikation of central hole to accolDmodIlte ae..... device.

-16-

2.25"

0.6" x 2.25" bolt, srade 6,

turned head .=0.6'7"

drilled .teel bar .iD,=1l/1S" ••ot=I"

half .phere 41=1.6"

full travel (adju.table)

Figure 2.7 Tension restraint sbo_iDa dimensions.

-17-

RIC TESTNATURAL RUBBER BEARINC WIlli TENSION DEVICE

HYSTERESIS LOOP

10 c:----------------r-----------------,

5

E'0RCE 0

KIPS "I

I-!; I

/ II,,

-10

-J -J -1 0 1

01 SPLACEMEm' INOiES

2

Figure 2.8 ElI'ed or tension device on horizontal stllmess.

-]8·

~ -11t-.-----~lO~---~::...:;..+r_

c- .-

t- ~ i""-3/18" point weld

(8)

•".+ -+

-~ I+- + -+-• 0.25" .. 0.25"~

0.25" 10" 0.25"-+1---------.;....-------~...

1/32" stainlt'ss st.-el plate

T l/S" .teel plate /

3/16" point weld (8)

Fipre ~.9 Tefton-stabaleu steel sUcler showilll cIi..nslons.

-19-

zz ~~ ;,);...J -- 00 uu

~M

XX ....,.

~~

W 8X31 nASE BEAM

snAKE TABLE load cell

10 x 7 lItAinlr!'l!lllteel mirror

·IX·l or liXr. t ..non layer (1/26")~~==:;:3

__Io~ked rubbt-r bearlns

lead pilip; bearing (empty)

Figure 1.10 Disposition 01 tension controlled bearing under comer columnand tefton-stainless steel slider under adjacent interior column,repeated 4 times lor the entire model.

-20-

CHAPTER THREE

TEST FACILITIES

1. Earthquake Simulator

The present experiment was conducted at the Earthquake Simulator Laboratory at the University

of California. The main facility is a shake table made of a 20)(20)(1 foot prestressed Concrete slab

weighing around ]00 kips. For the modcl used, the table efficiency dropped for frequencies higher

than 10 Hz. Vertical and horizontal motions can be independently applied. This is realized by three

horizontal 50 kip and four vertical 25 kip hydraulic actuators. The actuators arc located under the table

in a 22)(22)( 10 foot pit, built on massive foundations, and having a wall thickness of 5 feet. Air

pressure of up to 4 psi can be created in the chamber underneath the table. This carries the vertical

load of the table and the model and aIJows the vertical actuators to produce only the dynamic loads.

The total travel of the table is limited to IO inches horizontally and 4 inches vertically. The table

velocities and accelerations arc limited by the flow rate and the oil column resonance in the actuators,

respectively.

2. Input Signals

The signals used arc derived from previously recorded earthquakes, stored as digitized

accelerations. They arc described in chapter 5. Since the table is displacement controlled, these

accelerations arc double integrated and converted from digital to analog before being applied to the

table actuators through the MTS table controller.

Extensive work has previously been done on the repeatability of the table and its fidelity in

reproducing the signal as close to the original record as possible. The table motion characteristics are

not exactly Ihe same whether the lable is loaded or nol. Also, since the original accelerogram is

filtered below 0.] and above 24 Hz before being applied to the table, it may be more effective in

exciting very low and relatively high frequencies than is the table mOlion. Nevertheless, the main

characteristics of each earthquake were satisfactorily preserved.

-21-

J. Data Acquisition System

The main component in the data acquisition system is a VAX 750 computer connected to a

S-lOO minicomputer that performs a digital to analog conversion. After the conversion is done, the

command signal is sent from the S-lOO to the MTS controller. The MTS controls the table

displacements interactively.

Each measuring device installed on the structural model was connected to a channel. The

channels were read by a MULTIPLEXER that converts from analog to digital. The digitized readings

were then stored on the VAX 750 disk. then backed up on 9 track tapes.

The data acquisition capacity of the multiplexer is 50 KHz throughput and its burst rate is 300

KHz, in the sense that it scans the channels at the rate of 300.000 channels per second. and can read

up to 50.000 samples per second from each channel.

A maximum of 256 channels can be connected to a test model. In the present experiment, 128

channels were connected and data was acquired at the rate of 200 readings per second on each channel.

The data was then processed on the VAX 750 and SUN workstations.

-22-

CHAPTER FOUR

INSTRUMENTATION

Accelerometers, potentiometers. and direct current displacement transducers (DCDT) were

installed on the model. and force measurement devices under the base. Since the strains were expected

to stay in the elastic range. no strain measurements were made. Preliminary analyses provided levels

of response at which plastic deformations would be incipient. Nonlinear behavior can be detected by

examining the interstory drifts and comparing them with the deflections at which yielding would start.

1. Accelerations

Horizontal accelerations in the longitudinal direction were measured at each floor. at the vertical

plane of symmetry of the structure. Nine accelerometers were mounted on the steel girders for the

upper nine stories. and one on the concrete block at the base level. On the north-east and south-east

columns of the structure. two accelerometers were installed to measure transverse horizontal

accelerations at the ninth floor. Another six accelerometers were mounted to measure vertical

accelerations. Four of these were installed at the four outer corners of the base directly above the

isolalion bearings. and the other two on the middle plane of the ninth floor girder. The locations of the

accelerometers with their channel numbers are shown in Figure 4.1.

2. Displacements

Displacements in the horizontal direction were measured at each floor using potentiometers. Nine

of them were mounted on the upper nine steel girders, at the vertical plane of symmetry of the

structure. on the north side. Since they were connected to a fixed reference frame external to the table,

they were recording floor absolute displacements. Floor relative displacements. were obtained by

subtraction from the table displacements. At the base, however, two potentiometers were installed

between the outer north comers and the table. These measured base relative displacements at the

north-west and north-east sides. Their average was used in the study of the relative base displacement

-23-

response. Another two potentiometers were mounted on the east side of the base. at 3 feet towards its

center. from the outer nNth and south coraers. They measured relative displacements in these

directions. Their average was used in determining transverse base relalive displacements, and their

difference in examining torsional behavior. Displacements in the vertical direction were measured

using eight DCDTs. Four of them were installed at the four base outer corners and connected between

the top and bottom of the four external columns of the structure. These were intended to record any

axial deformations. Another four were mounted at the same locations in plane view. but connected

between the table and the top of the four external columns. These were intended to measure total

vertical deformations at the outer corners. The difference between the two sets provided the vertical

deflections in the bearings. However. since it was noticed that the axial deformations in the steel

columns were negligible compared with the total vertical deflections, the latter set of DCOTs was

directly used for bearing deflection calculations. They were also used to examine rocking movements

of the model. potentiometers are shown in Figure 4.2 and DCDTs in Figure 4.3.

3. Forces

Force measurements were performed at the base level only. The four exterior bearings were

mounted on load cells capable of measuring axial, shear. and bending forces. Two load cells were

installed in parallel under each of the bearings at the outer corners. Single load cells were used for the

four interior sliders. These internal ones. however. did not record either axial or bending forces due to

some instrumentation limitations. The static axial loads on the interior bearings were obtained by

calculation; since the measured axial loads carried by the external bearings were about 9 kips per

bearing. it was concluded that the internal bearings were carrying about 14 kips each. Equal

distribution of the axial loads among the outer bearings was achieved by careful shimming. Data was

recorded for static tests consisting of jacking and unjacking the structure at these individual locations.

Load cells locations and channel numbers are shown in Figure 4.4.

Table T-4.1 lists the channels assigned to the various measurement instruments installed on the

model. with their functions. Note that channels 1 through 12 correspond to the shaking table

-24-

accessories.

The structure was also tested fixed base with no load cells under its columns and the channel

numbering was changed. The fixed base structure instrumentation is shown in Figures 4.5 and 4.6.

Figures 4.7-4.11 show some photographs of the instrumentation on the base-isolated model.

".,5-

Table T-4.1 Channel list for hase isolated stMlcture.

LIST OF ~~~ELS fOR STRUCTURE ON:COMBINED RUBBER-SLIDERS SYSTEMMALAYSIAN RUBBER PRODUCERS RESEARCH ASSOCIATION (MRPRA) SET tl

CHANNEL NAME

1 hI disp2 h2 disp3 avg haec4 avg vacc5 pitch ace6 roll ace7 twist ace8 vI disp9 v2 disp

10 v3 disp11 h span12 hvel13 no1ax14 nolsh15 nolmo16 no2ax17 no2sh18 no2mo19 no3ax20 no3sh.21 no3mo22 no4ax23 no4sh24 no4mo25 so4ax26 so4sh27 so4nlo28 so3ax29 so3sh30 so3mo31 so2ax32 so2sh33 so2mo34 solax35 so1sh36 solmo37 ni2sh38 ni2mo39 si2sh40 si2mo41 silsh42 sllmo43 nilsh44 nilmo

UNITS

inchesinchesC'sC'srad/sec2rad/sec2rad/sec2inchesinchesinchesinchesin/seckipskipskip-inchkipskipskip-inchkipskipskip-inchkipskipskip-inchkipskipskip-inchkipskipskip-inchkipskipskip-inchkipskipskip-inchkipskip-inchkipskip-inchkipskip-inchkipskip-inch

REHARK

table horizontal actuatorl displ.table horizontal actuator2 displ.table horizontal accelerationtable vertical accelerationtable pitchtable rolltable twistnorth-west vertical actuator displacem.north-east vertical actuator displacem.south-west vertical actuator d~splacem.

applied table horiz. displacementtable horizonta~ velocity

north-west load cell #1/a~ialjbearingA2north-west load cell #1/shearjbearing A2north-west load cell ~l/momerljbearingA2no~th-west load cell #2/axialjbearing A2'north-west load cell #2/she~rjbearingA2north-west load cell #~/mcrnenjbearingA2north-east load cell #l/axialjbearing Alnorth-east load cell #1/shear/bearing Alnorth-east load c~l) #I/momenjbearing Alnorth-east load cell #2/axia1fbearing Alnorth-east load cell #2/shearfbearing Alnorth-east load cell tt2/momen/bearing Alsouth-east load cell #l/axialjbearing 01sou~h-east load cell #l/shearjbearing 01south-east load cell ttl/momenfbearing 01south-east load cell #2/axialjbearing 01south-east load cell #2/sheat"fbearing 01south-east load cell #2/momenjbearing 01south-west load cell ~1/axialjbearing02south-west load cell #1/shearfbearing D2south-west load cell #1/momenjbearing D2south-west load cell #2/axialfbearing 02south-west load cell #2/shearjbearing 02south-west ]oad cell #2/momenjbearing 02north-east load cell /shearfbearing 51north-east load cell /momenfbearing 51south-east load cell /shearfbearing Clsouth-east load cell /momenfbearing Clsouth-west load cell /shearfbearing C2south-west load cell /momenfbearing C2north-west load cell /shearjbearing B2north-west load cell Imomenjbear1ng 52

-26-

LIST Of CP~ELS fOR S7RUCTURE ON:COMBINED RUBBER-SLIDERS SYSTEMMAlAYSIAN RUBBER PRODUCERS RESEARCH ASSOCIATION (MRPRA) SET 11

CHANNEL NAME

45 nol totax46 nol parax47 n02 totax48 n02 parax49 s02 totax50 s02 parax51 sol totax52 s02 parax53 no: p:iisp54 sol pdisp55 sol rdisp56 s02 rdisp57 1st hdisp58 2nd hdisp59 3rd hdisp60 4th hdisp61 5th hdisp62 6th hdisp63 7th hdisp64 8th hdisp65 9th hdisp66 n02 vacc67 nol vacc68 s02 vacc69 sol vacc70 base hacc71 1st acc72 2nd hacc73 3rd hacc74 4th hacc75 5th hacc76 6th hacc77 7th hacc78 8th hacc79 9th hacc80 nc vacc981 no pacc982 sc vacc983 so pacc9

UNITS

inchesinchesinchesinchesinchesinchesinchesinchesinchesinchesinchesinchesinchesinchesinchesinchesinchesinchesinchesinc.hesinches9'59'S9'S9'59'59'59'59'5g's9'59'5g'sg'sg'sg'sg's9's9'S

REMARK

total axial deformation corner A2column axial deformation corner A2total axial deformation corner Alcolumn axial deformation corner Altotal axial deformation corner 01column axial deformation corner 01total axial deformation corner 02column axial deformation corner 02north la~eral relative base dlsplacementsouth lateral relative base displacementwest longitudinal reI. base displacementeast longitudinal reI. base displacementJst stc.ry absolute horizon. displacement2nd story absolute horizon. displacement3rd story absolute horizon. displacement4th story absolute horizon. displacement5th story absolute horizon. displacement6th story absolute horizon. displacement7th story absolute horizon. displacement8th story absolute horizon. displacement9th story absolute horizon. displacementBase north-east corner vertical acceler.Base north-west corner vertical acceler.Base south-east corner vertical acceler.Base south-west corner vertical acceler.Base horizontal acceleration1st story horizontal acceleration2nd story horizontal acceleration3rd story horizontal acceleration4th story horizontal acceleration5th story horizontal acceleration6th story horizontal acceleration7th story horizontal acceleration8th story horizontal a~celeration

9th story horizontal acceleration9th story north vertical acceleration9th story north. lateral horizon. acceler.9th story south vertical acceleration9th story south. lateral horizon. acceler.

Flpre 4.1

BASE ISOLATED

...

- ,- - «- \I ..... ~ \I." ,,\,

\--~ \

I ......... \

" '\'"

'" \/- '\, \

\

\

~I

Location and channel numbers ofaccelerometers on base isolated structure.

Figure 4.2

BASE ISOLATED

hd1sp

hd1sp

hd1ap

Location and channel numbers ofpotentiometers on base isolated structure.

I'"-:J

-28-

BASE ISOLATED

\\

" \

\,.... '

-f..., \I ... \

,/ ",

--I(1 ....I ,/

\.-."::;;r----::4.-4-:--.....;:~I----:r'""("--""t---:hf.=::--..,..~ S01 para"@

~=====:::t=====t:======\~' l~l tou"

n02

n02

Figure 4.3 Location and channel numbers or DeDTs onbase isolated structure.

-29-

-=::r- N ---

ni 2mo S12sh~ so3ax

noJsh ni2sh

no3ax

1--- --_.-.-.- ---------

.I I I It t ~ ~. .I I I I.

2--- _._. -- ._- ._-------

no2mo

no2sh nl.lmo

nl1sh

Figure 4.4 Location and channel numbers of load cells under base Isolated structure.

Figure 4.5

FIXED BASE

\

\\

Location and channel numbers ofaccelerometers on fixed base structure.

Figure 4.6

FIXED BASE

Location and channel numbers ofpotentiometers on fixed base structun.

.:...'?

.. ';'JiY"~~:'- ?Bsm..h' , ..._._ \

•

..

j

.........

Figure 4.7 Transversal (north) frame of the structureshowing horizontal accelerometers.

Figure 4.8 North-east corner: rubber bearing on loadcells, potentiometer measuring total verticaldeformation, accelerometer measuringvertical base acceleration.

Figure 4.9

-32-

j.- t"t..."!tII. ~ ..,:. .

, - '. _. to-

,...--

Side view of north rubber beadngs.

F1pre 4.10 Three channels of a corner load cell measuriDa axial,shear, and beadiag forces.

r ',. .•

·33-

-34-

CHAPTER FIVE

TEST PROGRAM

1. Table !\lotions

The table motions used were derived from eight different earthquake records. Horizontal and

vertical excitations were applied separately and simultaneously at spans ranging from 50 to 425, where

a span of 1000 corresponds to the maximum table displacement (~S in. horizontal, ~2 in. vertical). But

almost all inputs consisted of a horizontal component only. No rotational excitations were applied to

the structure.

The signals used were the EI Centro 1940. sOOc; the San Fernando Pacoima Dam 1971, sl6e; the

Parkfield 1966, n65e; the San Francisco (Golden Gate Park station) 1957, sBOe; the Taft (Lincoln

School Tunnel station) 1952. s6ge; the Mexico City 1985, s6Oe; the Bucharest (Romania) 1977, sOOe;

and the Miyagi-Ken-Oki (Japan) 1978, wOOs horizontal components. Before being applied to the table,

the original records were filtered (frequencies below 0.1 Hz and above 24 Hz were removed) then time

scaled by v'4 to maintain similitude. In the following description, the signal duration refers to the

duration of the table movement, not to the actual earthquake.

Table displacement and acceleration time histories corresponding to these earthquake signals, their

Fourier transforms, and their displacement, pseudo-velocity and pseudo-acceleration response spectras

for damping values of 2%, 5%, and 20% are shown in Figures 5.1-5.8. The period range was between

0.1 and 10 seconds for the displacement response spectra and between 0.1 and S seconds for the

pseudo-acceleration and pseudo-velocity. The eight inputs include earthquakes of varied frequency

content, durations and intensities. For instance, the El Centro component has a relatively wide range

of frequencies (between 1 and 5 Hz), and consists of about five significant cycles. It is commonly

used by structural engineers and is considered a typical California earthquake record. When run at 375

horizontal span, the table peak acceleration and peak displacement were around 0.7 g and 2 inches,

respectively. The Mexico City component is a low frequency, long duration (34 seconds) input. As

can be seen from Figure 5.2a, significant spectral amplitude is shown at 1 Hz to 2 Hz. The table

-35-

signal consists of two sets of several cycles over a very long duration. When run al 375 horizontal

span. a peak accderation of 0.18 g was produced on the table, and the peak displacement was about 2

inches. Throughout the testing program, the ~texico City record was the most severe input for base

isolation systems. The Bucharest record had relatively low frequency content (1 to 3 Hz) and short

duration. It consisted of uniformly decreasing and uniformly spaced displacement cycles. At 300

horizontal span, the peak table acceleration and displacement were about 0.27 g and 1.6 inches,

respectively. As for the Miyagi-Ken-Oki signal, the peculiarity was the large amount of energy at

around 2 Hz. The Parkfield signal provided a good test of the re-centering effect in the system, since

the table displacement time history for this signal consists of a large sway in one direction followed by

small cydes. The: signal is of medium duration with relatively wide spread frequencies. When run at

350 horizontal span, the peak table acceleration was around 0.4 g.

The highest frequency content was provided by the San Francisco signal. It consists of one pulse

of very large acceleration. followed by a slow large sway. At a horizontal span of 200. Ihe lable

acceleration reached 1.2 g. The table acceleration Fourier transform shows large spikes at about 5 Hz

and up to 8 Hz. The duration of the signal is very short (about 10 seconds). The San Francisco inpul

signal caused large base relative velocities able to activate the sliders at low spans.

This wide variety of input signals enabled different aspec;ls of the isolation effidency (It the

slider-bearing syslem 10 be studied.

2. Test Sequence

Table T-5.l shows a complete chronological listing of the tests. They are identified by file names

indicaling the date of the test as year, month and day, followed by a sequence number. File names

occupy the first column in Table 5.1. O>lumn 2 shows the short names of the signals. they are self

explanatory except "sct" which corresponds to Ihe Mexico City earthquake of 1985. The third column

lists the duration of each signal in seconds. The rate of data acquisilion is shown in column 4,

expressed as a fraction of a second between two consec;utive readings. It was set to 0.005, which

corresponds 10 200 readings per second. The span of the table motion occupies column S. The

-36-

geometric scale occupies column 6.

Since, to the knowledge of the authors, the new combined system had not been tested before, the

sequence was started with low span sinusoidal signals. These were, however. unable to activate the

sliders. The San Francisco signal for 50 and 100 horizontal spans was used next. It was noticed at

this point that the coefficient of friction of the sliders was rougHy 17 % which is about three times the

value provided by the manufacturer. A detailed study of the coefficient of friction and its variation

with velocity and axial load is presented in Chapter Six. The next table input was EI Centro 150

horizontal span. The span was gradually increased to 350. In between, a test including the EI Centro

vertical component at 300 span was run, The vertical component was expected to introduce variations

in the response since it afft:(;, the shear resistance of the sliders by changing the apparent weight of

the structure. However, no significant difference was noticed. This was due to the decrease in the

friction coefficient with increased pressure, resulting in a relatively constant resisting shear. Then, the

entire series of earthquakes mentioned in the previous section was run at this level of horizontal

displacement.

Because of the high coefficient of friction for the 6)(6 inch sliders, the base shears were very

high. Correspondingly. the model accelerations were relatively high. Since the coefficient of friction

of the teflon-steel drops when the pressure in the teflon increases, the dimensions of the sliders were

reduced to 4)(4 inches. These were tested separately on a static rig before installation. For a pressure

of around 900 psi and velocities between 1 and 10 in/sec., the average coefficient of friction was

around 12 O/C.

The tension devices installed in the bearings did not engage because the displacements were

decreased by the presence of the sliders. The initially allowed horizontal displacement of 2.25 inches

was reduced to 1.75 inches by tightening the restrainers from 0.8 inch to 0.5 inch slack. This was

done prior to the 861119 file series. Locking of the restrainers occurred for a low frequency, large

displacement Mexico City input at 375 horizontal span. The locking effect on the base shear stiffness

is shown in Figure 7.36 (right).

-37-

Throughout the entire test sequence. no significant damage of the teflon was noticed. However,

some conclusions wert: drawn about the durability of the teflon sliders. A thin white film due to

wearing of the teflon was noticed to "[-pear on '.he stainless steel after repeated testing. It was

periodically removed and the system retested. ~o difference, however, was noticed in the structural

response. Under a real building awaiting an eanhquake, the sliders are not expected to be used over

periods of many hours as they were during the test program. For this reason, the durability of the

sliders was considered very satisfactory for their purpose.

·38·

Table T-!.l Test program: listing or test I1Ins.

NINE STORY STEEL MODEL WITH K-BRACINGMASS DISTRIBUTION SHOWN IN FIGURE 2.1TOTAL WEIGHT OF STRUCTURE 91 KIPSBEARINGS: MALAYSIAN RUBBER PRODUCERS RESEARCH ASSOCIATION

(MRPRA) SET # 1

-------------------------------------------------------------fILENAME SIGNAL TIME RATE REMARKSB61015.01 ee2 19 sees .005 sph=150 ts=1/4861015.02 pae2 12 sees .005 sph=150 tS=I/4861015.03 park2 14 sees .005 sph=150 tS=1/4861015.04 sf2 12 sees .005 sph=IS0 tS=1/4861015.05 taft2 19 sees .005 sph=150 tS=1/4861015.06 buc1 12 sees .005 sph=150 tS=1/4861015.07 ee2 19 sees .005 sph=200 ts=1/4

comment: static tests were performed for shimmingby jacking and lowering at individuallocations and collecting data for axial load.

8&1015.08 static 15 sees .01 south end lift861015.09 static 15 sees .01 . north end lift

fILENAME SICNAL TIME RATE REMARKS861016.01 static 15 sees .01 south end lift861016.02 static 15 sees .01 north end lift

comment: changed shims and jacking again.

801e16.03 static 15 sees .01 north end lift861016.04 static 15 sees .01 south end lift861016.05 ec2 19 sees .005 sph=150 tS=1/4861016.06 ec2 19 sees .005 sph=lS0 tS=1/4861016.07 ec2 19 sees .005 sph=150 ts=1/4861017.01 sf2 12 sees .005 sph=150 ts=1/4861017.02 eel 19 sees .005 sph=225 ts=I/4861017.03 bue1 12 sees .005 sph=lS0 ts=1/4861017.04 pac2 12 sees .005 sph=150 ts=1/4861017.05 park2 14 sees .005 sph=150 tS=1/4861017.06 taft2 19 sees .005 sph=150 ts=1/4861017.07 pae2 12 sees .005 sph=225 ts=1/4861017.08 park2 104 secs .005 sph=225 ts=1/4861017.09 park2 14 sees .005 sph=250 tS=1/4861017.10 ee2 19 sees .005 sph=250 tS=1/4861017.11 sf2 12 secs .005 sph=225 ts=1/4861017.12 sf2 12 sees .005 sph=250 ts=1/4861017.13 taft2 19 secs .005 sph=225 ts=1/4861017.14 taft2 19 sees .005 sph=250 ts=J/4861017 .15 pae2 12 sees .005 sph=250 ts= .... /4861017.16 bue1 12 sees .005 sph=225 ts=1/4861021.17 bucl 12 secs .005 sph=250 ts=1/4861017.18 random30.d 35 sees .005 sph=300

FILENAME861021.01861021.02861021.03861021.04861021.05861021.06861021.07861021.08861021.09861021.10861021.11

SIGNALee2ee2random30.drandom30.drandom30.dec2sf2pac2park2taft2sf2

-39

TIME19 sees19 sees35 sees35 secs35 sees19 sees12 sees12 sees14 sees19 sees102 sec

RATE.005.005.005.005.005.005.005.005.005.005.005

REMARKSsph=150sph=250sph=300sph=600sph=900sph=150sph=150sph=150sph=150sph=150sph=250

tS=1/4ts=I/4

ts=1/4ts=1/4tS=1/4ts=1/4tS=1/4ts=1/4

comment: the following signals were run at low spansbecause the rigid body mode was at 0.75 Hzalmost in resonance with first sloshingmode of water tank mounted on structure.Data mainly collected for watpr tank .

861023.01861023.02861023.03861023.048&1023.05861023.068&1023.07861023.088&1023.09861023.10861023.11861023.12861023.13861023.14861023.15861023.16

eelee2eelsflsf2sf2pae2pae2park2park2taft2taft2bue1buc1setset

19 secs19 secs19 secs12 secs12 secs12 sees12 secs12 secs14 sees14 secs19 secs19 secs12 sees12 secs35 secs35 secs

. 005

.005

.005

.005

.005

.005

.005

.005

.005

.005

.005

.005

.005

.005

.005

.005

sph=50sph=75sph=70sph=50sph=150sph=75sph=50sph=75sph=50sph=75sph=50sph=75sph=50sph=25sph=25sph=50

ts=1/4ts=1/4tS=1/4tS=1/4tS=1/4ts=1/4tS=1/4ts=1/4tS=1/4tS=1/4ts=1/4tS=1/4tS=1/4tS=1/4ts=1/4tS=1/4

SLIDING BEARINGS. RUBBER BEARINGS. AND TENSION RESTRAINTSCOMBINED AS A NEW ISOLATION SYSTEM.

FOUR INTERIOR BEARINGS WERE 6X6 TEFLON-STAINLESS STEEL SLIDERSFOUR CORNER BEARINGS WERE NATURAL RUBBER BEARINGS WITH TENSION

DEVICES IN CENTRAL HOLES.

FILENAME861028.03861028.04

SIGNALstaticstatic

TIME RATE15 sees .0115 sees .01

REMlui.KSsouth end liftnorth end lift

comment: some sine signals were applied before the following~~ries. No sliding. Since expected high relativeveloci~1es to cause sliding, started with San Franciscohigh frequency record.

861029.01861029.02861029.03861029.04861029.05861029.06861029.07

fILENAME861030.01861030.02861030.03861030.04861030.05861030.06861030.07861030.08861030.09861030.10861030.11861030.12861030.13861030.14861101. 01

fILENAME861105.01861105.02861105.03861105.04861105.05861105.06

-40-

sf2 12 sees .005 sph=SO tS=1/4sf2 12 sees .005 sph=100 tS=1/4sf2 12 sees .005 sph=150 tS=1/4sf2 12 sees .005 sph=200 tS=1/4sf2 12 sees .005 sph=150 spv=150 ts=1/4ee2 19 sees .005 sph=150 ts=1/4ee2 19 sees .005 sph=200 tS=1/4

SIGNAL TIME RATE REMARKSee2 19 sees .005 sph=200 t.s=1/4ee2 19 sees .005 sph=250 tS=1/4ee2 19 sees .005 sph=300 t.s=1/4ee2 19 sees .005 sph&v=300 ts=1/4ee2 19 sees .005 sph=350 ts';1/4miyagi 13 sees .005 sph=350 ts::::1/4park2 14 secs .005 sph=350 t.s::::1/4t.aft.2 19 sees .005 sph=350 ts=1/4buc1 12 secs .005 sph=250 t.s=1/4bue1 12 sees .005 sph=300 t.s=1/4pae2 12 sees .005 sph=350 ts=1/4pae2 12 sees .005 sph&v=350 ts=1/4set 34 sees .005 sph=lSO tS=1/4set 34 sees .005 sph=250 tS=1/4ee2 19 sees .005 sph&v=300 ts=1/4

SIGNAL TIME RATE REMARKSsct.o 34 sees .005 sph=300 tS=1/4sct.O 34 secs .005 sph=350 tS=1/4set.o 34 secs .005 sph&v=350 ts=1/4ecatc.sl 23 sees .005 sph=250 tS=1/4eeate.s1 23 sees .005 sph:.:300 ts=1/4t.aftate.s1 23 sees .005 sph=300 tS=1/4

comment: by inspection of base shear l~steresis loops,it was noticed that the coefficient of frict.ionwas about 5 times the one provided by themanufacturer. It was around 20 7.. In ordert.o lower it, it was decided to increase thepressure on the teflon by reducing it.s area to4X4 inch.

INSIDE BEAR I NCS WERE 4X4 TEFLON-STAINLESS STEEL SLIDERS.

861117.01 ee2 19 sees .005 sph=150 ts=1/4861117.02 ee2 19 sees .005 sph=200 ts=1/4861117.03 ee2 19 sees .005 sph=300 tS=1/4861117.04 ee2 19 sees .005 sph=350 tS=1/4861117.05 ee2 19 sees .005 sph=400 ts=1/4861117.06 ec2 19 sees .005 sph=425 tS=1/4861117.07 sct.o 34 sees .005 sph=200 ts=1/4861117.08 sct.o 34 secs .005 sph=300 ts=1/4851117.09 sct.o 34 sees .005 sph=350 ts=1/4861117.10 set.o 34 sees .005 sph=375 tS=1/4B6ll17.11 ee2 19 sees .005 sph=150 ts=1/4

FILENAME SIGNAL TIME RATE REMARKS861118.01 ee2 19 sees .005 sph;;;150 tS=1/4B6ll18.02 set.o 34 sees .005 sph=400 tS=1/4

-41-

comment: the displacement eor.trol provided by the sliders~as such that the restrainers were not lockingat their initial adjustment of 0.8 inch whichallowed 2.25 inch horizontal freedom.Tension restaints were thus tightened to 0.5 inchbolt travel corresponding to 1.75 inchhorizontal freedom.

comment: oscillators were installed on the third fl oor and thei raccelerations recorded.

861119.01 ee2 19 sees .005 sph=300 ts=I/4861119.02 ec2 19 sees .005 sph=350 tS=1/4861119.03 ee2 19 sees .005 sph=375 tS=I/4861119.04 set.o 34 sees .005 sph=37S tS=1/4861119.05 buel 12 sees .005 sph=300 ts=I/4861119.06 mlyagl 12 sees .005 sph=3S0 tS=I/4861119.07 pac2 12 sees .005 sph=350 ts=I/4861119.08 park2 14 sees .005 sph=3S0 ts=I/4861119.09 sf2 13 sees .005 sph=200 ts=I/4861119.10 taft2 19 sees .005 sph=350 t~=1/4

861119.11 taftate.sl 23 sees .005 sph=32S ts=I/4861119.12 eeate.s1 23 sees .005 sph=32S ts=I/4861119.13 ee2 19 sees .005 sph=lS0 tS=I/4861120.01 ee2 19 secs .005 sph=150 ts=I/4861124.01 random30.d 32 secs .005 sph=100861124.02 square pulse 15 sees .005861124.03 sf2 13 sees .005 sph&v=250 ts=I/4861124.04 pae2 12 sees .005 sph&v=350 ts=I/4861124.05 set.o 34 sees .005 sph&v=350 ts=I/4861125.01 set.o 34 sees .005 sph&v=350 tS=I/4

NINE STORY STEEL MODEL WITH K-BRACINGMASS DUSTRIBUTION IN fIGURE 2.1TESTED fIXED BASE

-------------------------------------------------------------870622.01 random30.d 32 secs .005 int=.02 sph=250870622.02 ee2 18 sees .005 int=.OI sph=50870622.03 ee2 18 sees .005 int=.OI sph=100870622.04 eel 18 sees .005 lnt=.Ol sph=75870622.05 ee2 18 sees .005 int=.Ol sph=12S870623.01 sf2 12 sees .005 int=.OI sph=50870623.02 sf2 12 sees .005 int=.OI sph=75870623.03 sf2 12 secs .005 int=.Ol sph=1001370623.04 set.o 32 sees .005 int=.OI sph=100870623.05 taft2 18 sees .005 int=.OI sph=lOO870623.06 park2 12 sees .005 int=.Ol sph=12S870623.07 pae2 12 sees .005 int=.Ol sph=12S870623.08 bue1 14 sees .005 int=.Ol sph=150870623.09 buel 14 sees .005 Int=.Ol sph=175870623.10 miyagi 12 sees .005 int=.OI sph=lSO870623.11 miyagi 12 sees .005 int=.OOO90S sph=17S870623.12 random30.d 32 sees .005 Int=.02 sph=3S0

TABLE DISPLACEMENT inch.s DISPLACEMENT ffT

252010 IS

frwq HI.

5

O.Z

0.5 i ,

0.3

0.1

0."

0.0 ~ •~ ! i , , .Iao 01510

tl.- --=.5

2" I

o I ,II ~ I I I" II (.... '" \ I.... I

1

-2 k , t I I

o

';1

TABLE ACCELERATION q'. ACCELERATION FFT 1.1;J

252010 15

frwq HI.

51510

u..--=.5o

0.. 0.035 I I I I0.6 0.030

0." 0.025

0.2 0.020

0.0 0.015

-0.2 0.010-0."

O.OOS

-0.6 0.0 V' I, I I • I f,·'"r'I"'~~"'V*ie.lou:1-0.. ao 0

Fipre 5.la EI Centro 1940 sOOe, span=375, PTA.O,73 g.

·43·

a......

.."lilAI If!,\

} \I'

I I ,

1\,\

'\ \;.. .. - ,_._.-. "....-••••

10.10

o 1

- 2r;i·_••_... 5r'i•.•.•.•.• 2Or'i.

2 6

'.'0I •.••

..-I··...5 II-Do

.!&:l

....o I t •

Period (1IeC)I 10

Flawe S.lb Response spectn. El CeDtro 1940 sOOt, spao-37S, PTA-G.73 g.

TABLE DISPLACEMENT inches DISPLACEMENT FFT

:[ 0.35

.. I! I I 0.30

A I 0.25

0.2001 roL\nl"\'I,IIIII~1I111 \111I/lAP-\"I~A)_ I

0.15

0.10-1 ~ , U VII ~ If " I

O.OS

-2 II, , , . . . , 0.0

0 5 10 15 20 25 JO 35 0 5 10 15 20 25

tl8 .-c. frwq HI.

TABLE ACCELERATION 9'S ACCELERATION FFT~...[

I0.035

.JllliL 0.030

.. I I0.1 0.025

0.0200.0 I I ....'AIWU\AIIIIMJmJIAIHWIIMJlItAA& I

0.015

-0.1 ~ ." " 'III' I0.010

O.OOS~L&. _ .a.Jrr.a ... _ ...... • J••

-1.2 Ie. . ! . ! . , 0.0

0 5 10 15 20 Z5 30 35 0 5 10 15 20 25

tl-. .-c. treq".

F1aure 5.2a Mexico City 1985 s60e, span=37S, PTA=O.18g.

·45·

.......coit

1'1 ....."'!.5 'C-;I

IIAo

....o 1 2 3

--- 2';-------- 5':;-.- .- .•.• 20(';

" IlOO."

~

- '8~l $0.01

"'0.5 'C-,C-

....0 1 2 3 " &

ao."

10•" .Period (eee)

:........-,..:,~.:::.=-.:-._.- ._-----1

... ~&:II 10."E "l'Cll.- .-- ,~

.!Q I

'.~

)' .... - -....0 I

Fipre 5.1b Respoase spectra. Mexico City 1985 s60e, spaD-37S, PTA-O.18e.

TABLE OISPLACEMENT inches DISPLACEMENT FFT

252010 15

freq Hz.

0.40 I I0.35

0.30

0.25

0.20

0.15

:~~ ~l j , , , .I12 0 5104 6 8

t.UII .-::.

2

2.0 , I

1.5

1.0

0.5

0.0 I '..... I I I \ I 'J , \ r 'olV" " f

-0.5

-1.0

-1.5 II ' I , I , "

o

~'?'

252010 15

freq Hz.

5

0.0 V 1'1' ~r~rr"JV1··:V~ ..... ..,1o

ACCELERATION FFT

0,020

O,OlS

0.025 r I

O.oos

0.010

1210

g'5

4 6 B2

TA8LE ACCELERATION

tl-. .-::,

0.0 I """... ' llU 11'-'"11 ~'I

0.3 , i

0.2

0.1

, , t II-0.3 II • ,

o

-0.2

-0.1

Figure 5.3a Bucharest 1977 SOOf, span..300. PTA=O.27 I.

-47-

••••••

....

•. n

10."

o

o

I

1

2

2

a

I

- 2(';,-------- r,c'(-_ .•.•. - 20('(:

f &

...c:IIE

-ti~ Ie=-c.

.!C

'.00

•••• o I f •

Period (MlC)• 10

Flpre 5.3b Rapo... _pedn. Bucharest 1977 sOOe, spu-300, PTA.Q.27 I.

TABLE DISPLACEMENT Ihches DISPLACEMENT FFT

2 , I 0.4 i ,

-2 " . I , , • II

252010 15

freq Hz.

5

0.3

~~ Jl \'IlL.., . , ,0.0

o

0.1

0.2

121086

tiIa lI8C.

42o

o I < 1\ rJ \lIP I 1't,J • IHA ,., h f

1

-1 ~I

J.0/'

252010 15

fnq Hz.

5

ACCELERATION FFT

0.06 r<1:----------------.I

0.04

0.05

0.03

0.02

0.01

g's

tJ..B lI8C.

TABLE ACCELERATION

0.4, I0.3

0.2

0.1

O.O~

-0.1

-0.2

-0.3 [ • I I ~' """r,~ IO ....." 1Iwu.~ ", ..-0.4 . . , , , ..0 , ,

o 2 4 6 e 10 12 0

Fiaure 5.4. Mlyall.Ken.OId 1978 wOOs, span=3S0, PTA=0.33 g.

·49·

I."

8&",1 11 _ .M' .-1St _~......

- 2~;,

• -------..- rn.2iI _.- .•.•.- 2(t·i

- teoo 1! ~c 6::,.,. -a

l'•g.,

1.1'0 1 2 I 6,....

~

-1I t?6._ '0-;

g.,

-.-._._---_.-1.1'

0 1 2 I 4 i

I."

o 2 4 •

Period (eee)• 10

Fipre 5.4b RespoDSe spedn. Miyagl·Kea·Oki 1971 wOOs, Ipu-3S0, PTA-G.33 ••

TABLE OISPLACEMENT inches OISPLACEMENT FFT

2Szo10 15

freq HE.

5o

O.S i i

0.4

0.3

0.1

0.2

oJ~, , , , ,I121086

t1-.1MC.

42

2.0 I JIA I1.5

1.0

0.5 \ Io.oL~ J ~ >

-1~5 La .; I I , • II

o

-0.5

-1.0

, , « "-0.6 " • •

u.C?

2S2010 15

freq Hz.

ACCELERATION FFT

5o

~~,,0.0 V • I

O.OZO I i

O.OlS

O.OOS

0,010

1210

q's

t1-.8C.

4 , 82

TABLE ACCELERATION

o

0.0 I ..-lIlIl"Jtll II

0.2

-----------,.0.6 i

0.4

-0.4

-0.2

Fipre 5.5a Pacoima Dam 1971 sl6e, span..3S0, PTA:O.49 g.

·51·

.......c:.2~t

~1 1'0."u ~!6.5 ."-- :l

l.....

0

•••••J 2

- 'Jr.;••-._-_.. 1)(';

-'.'.'." Wr'i

._~_._.-._._._.

'.10

••••o 1 2 I .. &

.... .. .Period (Me)

• 10

FIpre 5.5b Respoase spect.... Pacoima Dam 1971 116e, Ipaaa350, PTA.O.49 I.


2.0 0.25

1.5 0.20

1.0 0.15

0.50.10 ~'

0.0 t S2 '?V~~~ Y ,I0.05

0.0-0.50 2 4 6 8 10 12 14 0 5 10 15 20 25

tl-. .-:. freq Hz.

TABLE ACC~LERATION q's ACCELERATION FFT V.';'"

0.3 0.014

0.2 0.0120.1 0.0100.0

0.008-0.1

0.006-0.2

-0.30.004

-0.4 0.002

-0.5 0.0

0 2 4 6 • 10 12 14 0 5 10 15 20 25

tl-. eec. rreq Hz.

Figure 5.68 Parkfteld 1966 n65e, span=JSO. YfA=O.41 g

·53-

......c:0-~Ii

~l?~.- ~-I~

••••0

Ie."

I I a

-2%------ 5%-.•.•.•.- 20%

..~

~

1 ii 11."......... ~.5 ~- i

~

••••0 I :I a .- i

I."

••••o I " .Period (eec)

• 10

FIpre 5.6b Rapoaae spectra. Parkfteld 1966 .65e, Ipa••35O, PTA-o.41a·


1.0 i I 0.30

O.S 0.25

0.200.0

O.lS

-0.50.10

-1.0O.OS t~

-1.5 Ie, , . , , . I 0.0' --

0 2 " 6 8 10 U 14 0 ~ 10 IS 20 ZS

u.. eec. ' .... Ik.

T.'.BLE ACCELERATION q's ACCELERATION FFTIU\

1.5~

0.030 ,

1.0 0.025

O.S 0.020

0.0 O.OlS

-O.S 0.010

-1,0 O.OOS

-1.5 0.0

0 2 4 6 8 10 12 14 0 5 10 IS 20 25

t18B eec. freq Hz,

Figure 5.7. San Francisco 1957 s80e, span=200, PTA=I.20 I.

-55-

.ra la.... .••s ....,•• ..-1/.

I\,

- 2C:;--------- Sc;;•.•.•.•. - 20(';

._._._._._._._._._._._._.

a......

c:.2~..- .!!

~I II

iu 1......

~

--- 6.5 ~~ :II

I~

....so ...

••••

••••

,.1

",

o

o

1

1

2

2

a

- - --a

&

&

..,acE a•••-- Ic:e. 'aJIQ

....0 J

._--._._.•.- -._.-

.. .Period (He)

• 10

Flpre $.7b Rapoase spectra. San Francisco 1957 dOe, .pan=200, PrA=1.20 ,.


252010 lS

freq Hz.

5

0.4 L i

0.3

0.2

0.1

l ~- I0.0 t ii' i

20 01510t:.l-. lMC.

5

1.0

2.0 i i

1.5

0.5

0.0' t { I "1 III I I ~ J'" f '0 I

-0.5

-1.0

-1.5 " ' , I ,

o

v.

'"

252010 1S

treq 11I:.

ACCELERATION FFT

5

0.025

0.020

0.015

o.oos

0.030 i i

0.010

q's

1510

U-IIC.

5

TABLE ACCELERATION

o

0.' -,------------,'0.6

0.4

0.2

0.0 I ...""-0.2

-G.' I. I. '11'~1-0.6 I " , . I 0.0 ~'t.._ _.&.,~_......, ~..:..:..~..:.::..:.:~_--::-0.' ' 20 0

Figure 5.S. Taft 1952 s6ge, span:350, PTA=O.72 g.

-57-

·......c::.2

-=- ..~ IIf. =:I : 101.11

......... '1

.5 %-~

='IGo ....

o 1

2(",--- /(l

---.-.... 5%-.•.•.•.• 20%

10."

ia21

, \

IV'\~

" " \(" L" \ .~I ." ~"""""'- ......,'. "._ .... _-.- ,

" -.:

o••••

11.'•

..C 10.&I- E

c II... ..--- c.oSQ

'.00

0 2 4 •Period (eec)

• 10

Fiaure 5.8b Response sped.... Taft 1952 s6te, span=JSO, PTA=O.72 I.

-58-

CHAPTER SIX

STATIC TESTS FOR SUDING BEARINGS

1. General

Te80n sliders have been used in bridges and other structures to accommodate changes in member

dimensions due to temperature and shrinkage effects. Since these movements are very slow, no

conclusions have been drawn about the performance of sliders under earthquake loading. In the

present experiment, sliders were ~ombined with elastomeric pads. mounted under the structural model

so that their behavior under earthquake londing could be better understood. In parallel with the shake

table tests, the sliders were tested separately on a static rig to study their characteristics in more detail.

Of great interest, was the variation of the coefficient of friction ~, with the pressure in the

material and the velocity of sliding. Generally, ~ increased with velocity and decreased with pressure.

Changes in ~ with the temperature and the cleanliness of the contacting surfaces are also a

subject of interest and should be further investigated. In this experiment, however, these two factors

were not studied since for sliders used in base isolation, the duration of activity is not long enough to

make temperature changes a primary concern.

Wear of the slider would be an important topic in applications where a very large number of

cycles is expected. This is not the case for an earthquake excitation. However, some results were

drawn from repeated testing.

Previous work has been done on te80n sliders in different test conditions [12], [13]. In [12), the

signal used was generated by the motor of a bulldozer and hence was not characterized by a constant

velocity. A triangular signal provides a better description of the effect of velocity on the friction

coefficient. In [13J, tests of teflon consisted of extremely slow displacements and were mostly

concerned with bridge joints. The sliding velocities used were of the order of 1% of the lowest

velocity used in the present program.

-59-

2. Test Machine and Data Acquisition

The test machine is shown in Figure 6.1. The main structural parts consist of a stiff fixed base

vertical column supported by two diagonal elements, and a horizontal beam located above the column

and controlled by two vertical and one horizontal hydraulic actuator. The actuators can be either force

conuulled ur displacement controlled. The two vertical actuators were force controlled. They were set

to apply a constant force p' each, in order to ensure an axial load of p. 2 P' on the bearing, located

under the center of the beam. The beam is very rigid in bending. Any vertical deftections in the

bearing would be automatically followed by the vertical actuators so that P remains constant.

The horizontal actuator was displacement controlled. in the sense that it was set to provide a

programmed signal. The nature of the displacement signal is chosen by the operator. In the present

experiment, two types of displacements were used, a sinusoidal time series and a triangular time series.

The force in the horizontal actuator was automatically changing correspondingly. At each actuator,

two channels were connected to record forces and displacements.

The sliders tested were 6)(6 inch and 4)(4 inch tefton layers bearing against a stainless steel

plate. The lower plate that carried the 1125 inch thick tefton layer was mounted on a rubber bearing

locked against horizontal movement (Figures 6.2 and 6.3). Between the bearing and the vertical

column of the rig, a load cell was installed (Figure 6.4). The load cell measured shear, and bending

forces.

Data was acquired through 15 channels. A list of the channel numbering and their functions is

provided in Table T-6.1. The data acquisition system, that included an MTS board (Figure 6.5), was a

part of the control instrumentation. A terminal permitted the display of all channels to check the

correctness of the displacement input and the constancy of the applied axial load. A mechanical

plotter, electrically connected to the shear and displacement channels produced simultaneously with the

beam movement, the hysteresis loops of shear at the slider versus displacement of the horizontal beam.

That was mainly intended to check if any deficiencies occurred during the test.

The rate at which the data samples are read is adjustable. For the slow runs, namely

corresponding to 0.0125 Hz. the data was read at a rate of 10 readings a second. For the tests

-60-

corresponding to 0.125 Hz, 50 samples were acquired per second. For all higher frequencies of input

displacement, 100 readings per second were performed. Each set of data acquired was temporarily

stored on the disk of the computer until it was saved on tape, loaded on a VAX 750, and processed.

3. Test Sequence

The vertical loads and velocities used in the rig tests were intended to include their corresponding

values encountered during shake table tests. While mo\;nted under the structural model, the inner

bearings carried about 14 kips each, and the outer ones around 9 kips each.

For the teflon sliders, the 6x6 inch layers were hence under a pressure of about 390 psi while

installed under the structure. On the static rig. their pressure was varied from 100 psi to 1200 psi.

The 4x4 inch layers were subjected to about 900 psi during the shake table tests, and their pressure on

the static rig was varied from 100 psi to 3000 psi. The pressure was extended to that high value in

order to detect any deficiencies that could result from accidental overloading of a slider during an

earthquake.

Table T·6.2 provides a chronological listing of the series of tests performed on the static rig. In

the first test series, which is not listed here, sinusoidal signals of various frequencies and amplitudes

were used as horizontal displacement input. Since the slope of a sinusoidal signal is continuously

changing, the sliding velocity was not fixed to a certain value. Furthermore, the shape of the

hysteresis loops for those tests were close to elliptical, and thus did not show a constant shear force.

That suggested that the friction coefficient depended greatly on the sliding velocity. The highest point

of the hysteresis loops was located on the vertical axis, this showed that the coefficient of friction

increased with velocity.

For the reasons mentioned above, it was decided to use a displacement signal with constant slope

(triangular signal) to study the effect of the velocity on the coefficient of friction. The values that were

used were intended to cover the range of velocities produced on the shake table. Integration of the

structure base relative acceleration time series, produced relative velocities up to 12 in/sec for certain

shake table tests.

-61-

4. Test Results

The displacement and shear time histories for the 3 or 4 main cycles of each test run along with

the corresponding hysteresis loops are shown in Figures 6.8-6.22, for the 4x4 sliders. The values of

the resulting coefficients of friction are summarized in Table T-6.3 and plotted in Figure 6.23. The test

was mainly intended to study the coefficient of friction of the sliders and its dependence on the

following factors:

Velocity

Even though it is commonly accepted that for most contacting surface!. the static coefficient of

friction is higher than the dynamic coefficient of friction. it was noticed that for very low velocities.

namely 0.1 in/sec. the coefficient of friction was lower than the one obtained for higher velocities.

For instance, for the 4x4 sliders, I.l changed from 7% to 17% when the velocity was increased

from 0.1 to 10 in/sec, for a pressure of 100 psi. and from 6% to 15% for the same velocity variation,

but under a pressure of 1200 psi in the teflon. However. this increase tends to a certain saturation at

velocities around 12 in/st'c. For velocities of above 12 in/sec. the shear level drops within the same

test run, because of the increase in temperature at the contacting surfaces, producing a lower coefficient

of friction. For these tests, the coefficient of friction adopted was the one that corresponded to the

three full middle' cycles in the input displacement time history. This coefficient was generally smaller

than the one obtained at the first cycle of the signal.

Pressure

Another property of the tefton sliding on stainless steel is the dependence of its dynamic

coefficient of friction on the pressure in the material. In general. for most sliding areas, the dynamic

coefficient of friction is obtained from simply normalizing the shear resisted by the slider by the axial

load. at a certain rate of sliding. In the present case, the value of the axial load had a large inftuence

on j.l. For instance. a change of 1100 psi in the pressure at 10 in/sec. caused a drop in 1.1 from 17% to

7%.

-62-

On the other hand, the static coefficient of friction. which was adopted as corresponding to

v • 0.1 in/sec, was not affected by the changes in axial load; for • difference of pre~ure of 1100 psi,

IA stayed around 7%.

Temperatu"

Depending on the fabrication process and the composition of the tefton, the temperature has

different effects on the coefficient of friction. This experiment gave only a general i~e'l of the effects

of temperature. The slider was estimated to be at room temperature before tht' test, l'.nd at around

lUfF after the test, for velocities of 10 in/sec and above. Since it was not intended to study

temperature effccts for our present application, no instrumentation was installed to acquire the

temperature time history. In sum, the effect was a slight drop in ....

Contamination

It is commonly accepted that the presence of an external material between the contacting surfaces

causes substantial changes in IA. In reference (12], data for greased sliders and dusted sliders is given.

Since a building is expected to be always resting on its foundations, no other material will penetrate

between the contacting surfaces. The area of steel which is not constantly covered by the tefton, can

be regularly cleaned of a contaminating material as a part of the maintenance program.

Wear

After 60 test runs equivalent to about 250 cycles of an aVerlle amplitude of 1.2 inches, the te:flon

layer thickness was reduced by only 1/30 inch. The main type: of wearing noticed was a delamination

of the tefton layer (Figures 6.6 and 6.7). After tests of v • 10 inlscc: and above: were performed, very

thin layers of tefton of areas of about 4 square inches detached from the sliders. Also, on the stainless

steel plate, a white film was found after each test. This film was removed by each following test run

and a white powder-like material was found on the steel at the limit of travel of the tefton.

-63-

For comparison. the teflon fragments were cleaned from the steel and the same test was rerun

with a slight increase in the coefficient of friction. The difference. however, was negligible and the

removal of the teflon film after each run was found unnecessary. There was some hesitation in

identifying this delamination as damage, since it had almost no effect on the coefficient of friction.

Also. the reduction in the thickness of the teflon was very small. Under earthquake excitation, the

number of cycles is too small to cause a concern about the wearing in the slider.

Strength

At the end of the test program, the pressure on the teflon was increased to 3000 psi to test the

strength of the slider. No noticeable change was observed. other than the decrease in the coefficient of

friction in about the same proportion as for the previous pressure levels. No fracturing in the 1/30

inch thick teflon layer occurred. This showed that there is no risk of failure of the teflon or sudden

changes in the slidel properties in the case of an accidental overloading. At this level of pressure,

however, the delamination was slightly increased.

Previous experience with teflon in slow movements, and recent research on its performance under

dynamic excitations show its reliability and the possibility of using it as a component in base isolation

systems.

-64-

Table T-6.1 List 01 channels lor trlanplar slpal rig testing.

LIST OF CI-WmELS FOR TEFLON-STAINLESS STEEL SLIDERSSTATIC RIG TESTING.

CHANNEL NAME UNITS REMARK

o12345&7B9

101112131415

F.L.DCDTB.L.DCDTF.R.DeDTB.R.DeDTFoC .DeDTB.C.DeDTHOZ.LOADHOZ.DISPVPM SHEARVPM MOMENTVERT. LOADlVERT . LOAD2VERT.DISP1VERT.DISP2VPM AXIALVPM DlSP

INGlESINCHESINCHESINGlESINGlESINGlESKIPSINGlESKIPSKIP-INKIPSKIPSINCHESINCHESKIPSINCHES

Front Left DCDTBack Left DeDTFront Right DCDTBack Right DCDTFront Center DCDTBack Center DeDTHorizontal actuator forceHorizontal actuator displacementShear recorded on load cellMoment recorded on load cellVertical actuator II forceVertical actuator 12 for'ceVertical actuator 11 displacementVertical actuator 12 displacementAxial force recorded on load cellAxial displacement betweenload cell and ground.

-65-

TabieT-U SUden test sequence for tri.n....r ........

TEST SfQUENCE fOR 6x6 AND 4x4 TEFLON-STAINLESS STEELSLIDERS fOR TRIANGULAR HORIZONTAL DISPLACEMENT.4 MINUTES REST BETWEEN SUCCESSIVE RUNS.----------------------------. __ .- ---------------------.Collecting data at 10 samples/sec for 0.0125 Hz .•

50 samples/sec for 0.125 Hz ••50 samples/sec for 0.625 Hz .•100 samples/sec for other frequencies.

Testing 6x6 slider------------------

FILENAME VELOC FREQ AXIAL PRESS AMPLITIn/s Hz Kips psi in

870305.01 0.1 0.0125 3.6 100 2870305.02 1.0 0.125 3.6 100 2870305.03 5.0 0.625 3.6 100 2870305.04 10.0 1.25 3.6 100 2870305.05 12.0 1.50 3.6 100 2870305.06 15.0 1.875 3.6 100 2

870305.11 0.1 0.0125 21.6 &00 2870305.12 1.0 0.125 21.6 600 2870305.13 5.0 0.625 21.6 &00 2870305.14 10.0 1.25 21.6 600 2870305.15 12.0 1.50 21.6 600 2870305.16 15.0 1.875 21.6 600 2

870305.21 CI.1 0.0125 32.4 900 2870305.22 1.0 0.125 32.4 900 2870305.23 5.0 0.625 32.4 900 2870305.24 10.0 1.25 32.4 900 2870305.25 12.0 1.50 32.4 900 2870305.26 15.0 1.875 32.4 900 2

870305.31 0.1 0.0125 43.2 1200 2870305.37- 1.0 0.125 43.2 1200 2870305.33 5.0 0.625 43.2 1200 2870305.34 10.0 1.25 43.2 1200 2870305.35 12.0 1.50 43.2 1200 2870305.36 15.0 1.875 43.2 1200 2

The temperature for the previous tests raised fromroom temperature to around 100 F at the stainlesssteel face. The plate vas varmer. but no othersignificant differences. Waited until coo11ng thenstarted vith 4x4 slider.

-66-

Testing 4x4 slider------------------FILENAME VELOC FREQ AXIAL PRESS AMPLIT870305.41 0.1 0.0125 1.6 100 2870305.42 1.0 0.125 1.6 100 2870305.43 5.0 0.625 1.6 100 2870305.44 10.0 1.25 1.6 100 2870305.45 12.0 1.50 1.6 100 2870305.46 15.0 1.875 1.6 100 2

870305.51 0.1 0.0125 9.6 600 2870305.52 1.0 0.125 9.6 600 2870305.53 5.0 0.625 9.6 600 2870305.54 10.0 1.25 9.6 600 2870305.55 12.0 1.50 9.6 600 2870305.56 15.0 1.875 9.6 600 2

870309.01 0.1 0.0125 14.4 900 2870309.02 1.0 0.125 14.4 900 2870309.03 5.0 0.625 14.4 900 2870309.04 10.0 1.25 14.4 900 2870309.05 12.0 1.50 14.4 900 2870309.06 15.0 1.875 14.4 900 2

870309.11 0.1 0.0125 19.2 1200 2870309.12 1.0 0.125 19.2 1200 2870309.13 5.0 0.625 19.2 1200 2870309.14 10.0 1.25 19.2 1200 2870309.15 12.0 1.50 19.2 1200 2870309.16 15.0 1.875 19.2 1200 2

980309.21 0.1 0.0125 32.0 2000 2980309.22 1.0 0.125 32.0 2000 2980309.23 5.0 0.625 32.0 2000 2980309.24 10.0 1. 25 32.0 2000 2980309.25 12.0 1.50 32.0 2000 2980309.26 15.0 1.875 32.0 2000 2

870309.31 0.1 0.0125 40.0 2500 2870309.32 1.0 0.125 40.0 2500 2870309.33 5.0 0.625 40.0 2500 2870309.34 10.0 1.25 40.0 2500 2870309.35 12.0 1.50 40.0 2500 2870309.36 15.0 1.875 40.0 2500 2

870309.41 0.1 0.0125 48.0 3000 2870309.42 1.0 0.125 48.0 3000 2870309.43 5.0 0.625 48.0 3000 2870309.44 10.0 1. 25 48.0 3000 2870309.45 12.0 1.50 48.0 3000 2870309.46 15.0 1.875 48.0 3000 2

clockwise tilt of 0.04 rd. for 870309.47counterclockwise tilt of 0.04 rd for 870309.48

870309.47 10.0 1.25 48.0 3000 2870309.4~ 10.0 1.25 48.0 3000 2------------------------------------------------

-67-

Table T-6.3 Variation or friction coellklent for 4,,4 inch teflon-stainless steel slide"with pressure and sliding velocity.

. COEFFICIEl\\T OF FRICTION ( % ) - .. x 4 TEFLON SLIDER

. 100 psi 600 psi 900 psi 1200 psi 2000 psi 2500 psi 3000 psi

0.1 in.au I 6.9 6.8 6.4 6.4 6.6 6.3 5.0

1.0 in. ate . I 11.7 11.5 11.1 11.1 10.2 8.8 7.9

5.0 in.,tc . I 16.9 16.7 14.5 13.2 10.3 9.0 8.3

10.0 "ute I 17.5 17.2 ]5.9 15.0 11.0 9.5 8.7

12.0 in.ate I 17.2 16.7 15.0 14.6 10.7 9.4 8.3

15.0 in.3CC I 17.1 16.6 14.9 14.2 10.2 9.1 7.9

--68-

Flpre 6.1 Ria used for slider tests.

·69-

Figure 6.1 The three basic components: rubber bearing, teflon,stainless steel plate.

Fi,ure 6.3 SUder as mounted on the static ria.

-70-

Figure 6.4 Slider on load cell.

-71-

:~I'.II.

I•

I

-72-

Figure 6.6 Tenon slider after repeated testing (250 cycles).

Figure 6.7 Tefion wearing by delamination.

·73-

2 =:------------------------.

k· .hf-----------+----------~C

J-1

-21:- -L l..- -:... ---J

-2

Flaure 6.8 Displacement. shear, and hysteresis loop lor 4x4 Inch slider,y-G.l In!sec, p-!JOO psi.

-74-

RIC TEST V~S.O in/see - p~900 psi

zo I

l ::1 /\ ,/ \ /\E -::f V \;/ V'

-10 r-15 •

I-z.o ~------------------------• •-- 1 •

"•p•

o : \ I' \ / \ )-z • V- l.---' ...---r-4 t..- ~ ~ _

• 10

a.•1.'1.0•••0.'W7U~U

" """""'" III

I

J--..J.' -1.' -1.' .•.•

"1~

Fipn 6.9 Displacement, ,hear. and hystensis loop for 4x4 inch slider.".5.0 in/sec, p=900 psi.

-75-

RIC TEST V:l~.C J..,/sec:

1n,II••

-I r

.J~l -'• _.... • •

••

:1 "\ nr1 n(\ r°1-----------.-1.:..-i_I-+\....,..I-+--r-II;......;..'--

iii I ! I I i \ i~t wu wu W-4 Lt --l

g

10•p·

-:-: ::::~

•=F----------,----------,

I

\

1

I ~

~ ~r1

I

l \.-.....::::::

I1

"1e

-I

-.-I -1 o--

Flpn 6.10 Displacement, ihear, aad hysteresis loop for 4x4 inch slider,v-U.O In/sec, p-900 psi.

RIC; TEST

-76-

v=o 1 1n/sec 0 p=120~ ps~

,"c 0

".•-1

-~

0 --2

1

3

[ --"\ -----" "~k~l 0 Il__\~----.I:.--'------_~'\ /- \ I~ ~---P/----r-l-J-"--';""I---'

:::....-...-1 ~_

1 ;-

III

1 ~

I

JI

iIt i1 o·~

-1

0 1 ,

II

-1

-1 -1

100 no........'i';-.)r,;;.~

300

2

Flpre 6.11 Displacement, shear, and hysteresis loop for 4x4 inch slider,v-O.l in/sec, p=lZOO psi.

-77-

• ~i--------------

I

~--='--,

I

I I

-...;;:::

k

•C

-I

-...

-1.0 -1.1 -1.' •••• ••• •••-_1:1

1.0 1.' I.'

Fipre 6.12 Displacement, shear, and hysteresis loop lor 4x4 inch slider,v-S.O lnisec, p-1200 psi.

,,...-----------r-----------,

..

k•~

•

•

l~

I

\.~

•.,.... 1

Fllllre 6.13 Displacement. shear, and hysteresis loop for 4x4 Inch allder.v"S.O In/sec, p-1200 psi.

-79-

RIG TEST V=O.l in/sec . p=2000 ps~

•"·II·•

\

\\

-1

-2 L- _

:I·f----:-I'-~\--il:....-~_........\_---J-I'_---.;\_I \ I I • \

- ' ------. I\..-__ ! V---J r

..l=---- ~ _

k•p•

100 150

...

k1

r

-1

-4 "'- .....J. ..I- ...;.. --II

-2

Flpre 6.14 Displacement, sbear, and hysteresis loop for 4x4 lneb slider,v".1 In/sec, pz:ZOOO psi.

-80-

....

~- ,r

~ -...;,;;

i

•

•

-J

..• J

..

k1

~

Flaure 6.15 Displacement, shear, and hysteresis loop for 4x4 inch sUder,vaS.O In/sec, p=2000 psI.

-81-

ruc TEST

•

4

•1~

-4

F

\

i~ -I V-

l r "i

I

I

'-.'-.;

,

,o--- I

Flaure 6.16 Displacement, shear, and hysteresis loop for 4x4 Incb .Ider,v-IS.f\ in/see, p.2000 ps!.

p.le TEST

-82-

v=e 1 in/see - p=2500 pSi

1

"c"••

k1P•

-1

-2 t..- _

--

:1__..--/'1-+-\_~I~_\_~r----.;,.\_....;-I_\ I \ I \ !

I I I:t'-- .._------. ~v-----v~__. i.-- \l__....:

k1

~

-2

100 110 JCO 30<

-1

-4~ .l__ .l._ .:...._ ___"

-2

P1pre 6.17 Displacement, shear, and hysteresis loop for 4x4 inch sUder,v-G.l in/sec, p-1500 psi.

-83-

RIC TEST V=5 0 In/SeC • p~2S00 pSi

1ncto•. 1\

ol-----------------T---i--":---I'---+--iC-.-_+_~

-1

.~ L- ----'

• •--- • 1D

•..OJ09D

"I

I

I\

~L ~

I '"II~

\

f b..'-- ~

•

•

-I

II1;

"lUft 6.18 Displacement, shear, and hysteresis loop for 4x4 Inch sUder,v-S.O in/'.ec, p-2500 psi.

-84-

~lC TEST V=15.0 in/sec - p"2500 psi

•"c"·•

::t0 • • 10 l~.......

•• 'I r'1 nnr~ I . I..

• \ ,p

! , I I! II•·2 I, I

, '.) ~ lJ ~ L.:

J0 • • • 10 1~--e;glOili16

•---

[-~

~

I

\ t-...:...;'

,

•

..-3

Flpn 6.19 Displacement, shear, and hysteresis loop for 414 Inch slider,,,-15.0 In/sec, p"15OO psi.

-85-

R1C TEST

1nen••

-I

-2 t, no JOo---:I _J\ I 1\\

, \k

o II \

1

" I I I• I I l-2 f \.,... I \.r J V-I \i

04 t

0 so 100 1502 100 25Il

~~

k1

C

-l

-4 L ..-L -:- ~----_:

~ ~ ...-Figure 6.20 Displacement, shear, and hysteresis loop for 4x4 inch sUder,

v=O.1 in/sec, p=JOOO psi.

-86-

RIC TEST V=5.0 in/sec - p~3000 Fsi

J•...-

~

~

~J- --:::::::r

-4

-J

o

4

oJ

..

k1

=

FIpn 6.21 Displacement, shear, and hysteresis loop for 4x4 loeb sUder,,,-5.0 In/sec, p-3000 psi.

-87-

RI::; TEST V:15.0 in/sec . p-3000 psi

r 0 ~ r\1 ,\ I \ 1\

" I I ' , /,eh

~! \1 ~; \I \ I••

-I ' ~ I \,: oj

·z• • • 10 ..--

••

:~nn~• 0p

JuJUU•

.J....4 • • 10 1Z_....

'"7ClO_

-.

•I'll_

I

I

1 --~

- ~

II

I

\. j

1~

•

•

.J

.. .,

..• 0~

Fi&Ure 6.12 Displacement, shear, and hysteresis loop for 4x4 inch sUder,,,"5.0 in/sec, p-3000 psi.

TEFLON SLIDER 4X4 INCH

..'

_.- ~

16

- -- - - -

I I 1 __

10 12 14

----------- .. :"=:--------- -- -_._- ----

-- -~-- .. --_ .. __ ._-._--- - ... -

___ 0- _. ._._. __ • __ • _

--------

-~-~-_.-

p '" 100 FBi --IP '" 600 psi

P '" 900 psi

P= 12OO~~JiP'" 2000 psi

P '" 2SOO psi

p'" 3000 psi

·r...···;···· .,//--_._---------_._---------_._-

II .-f/ I - _.- -~: . .- - - - -'-,,1.'1- - - - - - - - --- _._-_.-.- --l :.'1 - - - - - - - - - - - -.N ---

:/ If/

o5 t-L I I I I

Z 4 6 8

25

20

15

10

FRICTIoN

CoEFFICIENT

%

VELOCI1Y IN/SEC.

Figure 6.23 Variation of friction coefficient with velocity and pressure.

-89-

CHAPTER SEVEN

EARTHQUAKE SIMULATOR TEST RESULTS

1. General

It is commonly accepted that isolation systems consisting of solely rubber bearings provide

substantial reduction in ground accelerations transmitted to the structure. However, this reduction in

accelerations is accompanied by an increase in base drift and a lack of wind restraint. The system that

combines sliders and rubber bearings provides a better displacement control and an inherent wind

restraint. For the structure mounted on elastomeric bearings only (MRPAA SET #1), the mode

corresponding to its fixed base fundamental frequency of 3.4 Hz was almost totally attenuated. The

only significant peak in the Fourier transfonns of the base and story accelerations corresponded to the

frequency of rigid body motion of the structure at 0.7 Hz. When the sliders were added, the fixed base

structure fundamental frequency appeared again. This is illustrated in Figures 7.1, 7.2 and 7.3 which

show the Fourier transfonns of table, base, third, sixth, and ninth story accelerations for EI Centro at

200 span, Bucharest at 250 span, and Mexko City at 50 and 150 span, J4 time scaled records for the

two isolation systems. That was due to the fact that the response: of the structure had two distinct

states; one corresponding to a base shear level below the sliding threshold, needed to activate the

system, and the other to a base shear above it. In the first state the structure responded as if it were

fixed base, while in the second state, the stiffness of the rubber bearings controlled and the first mode

was the rigid body mode of the structure on a solely rubber isolation system. By comparing the

responses between different spans for the isolation system that included sliders, it was noticed that the

base relative displacement plays an important role in the pattern in which the energy is distributed

between these two modes. When the span is larger, the combined system behaves more like a solely

rubber system because of the increased participation of the rubber.

If an equivalent stiffness were to be determined, it would depend on the maximum base relative

displacement and could be used only if an approximate idea were sought for a preliminary design

phase. A different simple approach yields far more accurate results. A bilinear force displacement

relationship with infinite initial stiffness followed by the stiffness of the four rubber bearinp, was

-90-

found very adequate to model the combined isolation system. For the superstructure, static

condensation can be used and the OVtrall analysis can be perfonned on a simplified modtl where all

elements "ie elastic except at the base.

2. Displac:emeDu

One of the advantages of the combined sliding bearing rubber bearing system was the reduction

in the relative base displacements, due to the energy dissipation provided by friction, and to the

increased base shear needed to stan the base movement. FiguR's 7.4, 7.5 and 7.6 show base shear

hysteresis loops for the MRPRA SET NI and for the combined system. The respective peak base

displacements for the MRPRA SET Nl system and the combined rubber-sliders system were 2.06 in.

and 0.77 in. for the EI Centro record at 200 horizontal span (1 in. peak table displacement) yielding

2.06 and 0.77 as base displacement amplification ratios for the two systems respectively; 2.57 in. and

0.94 in. for the Bucharest record at 250 horizontal span (1.25 in. peak table displacement) yielding

2.06 and 0.75 as respective base displacement amplifications. Under the Mexico City input, the peak

base displacement for the MRPRA SET Nl was 0.11 in. at SO horizontal span (0.25 peak table

displacement), while it was 0.09 in. for the combined rubber-sliders system at 1SO horizontal span

(0.75 in. peak table displacement), yielding base displacement amplitudes of 0.44 and 0.12,

respectively. In sum, the rubber system amplified the base drift about 3 times more than the combined

rubber-sliders system did. Previous tests of rubber systems showed excessive base drift under low

frequency inputs, like the Mexico City signal, and the span for those excitations had to be kept under

150. While using the slider-bearin, system, we were able to apply horizontal spans up to 400 (2 in.

peak table displacement) for the Mexico City record, resulting in a peak base displacement of only

about two inches.

Deftected shapes of the structure at the instants when each story individually reached its

maximum displacement are shown in Figures 7.7-7.14. It was noticed that the presence of the sliders

in the proportion used (31 % of the total bearing arca, carryin, 609lI of the total weight) did not

chaJIae the maiD effect of an elutomeric: base isolation system, that is causing the struaure to move

-91-

like a rigid body. The deflected shapes at instants of maximum displacemtnts also showed the

predominance of a bast-isolattd first moot. For instance for the Mexico City signal at 375 span the

story drifts at t=21.9 sec. were 0.13, 0.08, 0.08, and 0.07 in. for the first. second, third and ninth

storitS, rtSpectively, while the base drift was 1.91 in. For the Bucharest table motion at 300 span the

story drifts at t=3.2 sec. wtre 0.12, 0.04, 0.05, and 0.02 in. for the first. second, third and ninth

storitS while the base drift was about 1.3 in. For the San Francisco record at 200 span the story drifts

at t=2.4 sec. were 0.07, 0.05, 0.05, and 0.03 in. for the first, second, third and ninth stories,

resptctively, with a base drift of 0.84 in. In sum, for most table motions, base displacements were

largtr tban story drifts by a factor of 10 to 15. The magnitudtS of the base displacements, however,

depended on the type of signal applied. Table T-7.1 summarizes rtSults for eight different earthquakes

at different spans.

The structural model was also tested with its base fixed to the shake table. Time histories for the

story drifts of the structure on the combined rubber-sliders isolation system were compared with the

corresponding ones for the fixed base condition. The spans for all earthquake records applied to the

isolated structure were larger than the ones applied to the fixed base structure by a factor of 2 to 3, yet

resulting in story drifts of about the same magnitude. For instance, the maximum story drifts for the

third, sixth and ninth stories under the San Francisco signal applied at 100 horizontal span (PTA=O.7

g) were 0.07, 0.07 and 0.04 in., rtSptCtively, for the fixed base condition, while they were of 0.06,

0.06 and 0.05, resptCtively, for the isolated structure on the combined system for the same signal at

200 horizontal span (PTA=1.2 g). This is illustrated in Figure 7.15. The choice of the quantity to

which these values can be normalized in order to obtain a more precise comparison when the applied

excitations havt different magnitudes is debatable, esptCially because story drifts depend on both input

displacements and input accelerations.

The relative base displacement time histories were of particular interest for studying the

recentering provided by the rubber bearings. FigurtS 7.16-7.19 show the table ax:eleratioo, table

displacement, and base drift time histories for the eight earthquake records used. The largest offset

encountered throughout the whole testing program corresponded to the Mexico City input and yet was

-92-

only about 0.2 in. for a peak table displacement of 1.9 in. The recentering capacity of the system is

particularly illustrated in Figure 7.18 (top, right) showing the base drift for the Parkfield input at 350

horizontal span. The table displacement time history shows a significant sway of 1.8 in. in one

direction followed by small amplitude cycles of less than 0.5 in., the base, however, recentered with an

offset of only 0.04 in. This shows that very small cycles are enough to recenter the system even if

they are precedeJ by a strong ground motion in only one direction. The end-of-signal base offsets arc

shown in Table T-7.2 with their corresponding peak table displacement and peak table acceleration.

In a previous study of the sliding response of rigid blocks under earthquake excitations by Aslam

et al. (11), a massive 3x2d ft concrete block weighing 935 Ib was free to slide on a 6)(6)(0.5

protective concrete slab which was hydrostoned to the shake table. Various materials were used

between the block and the slab to change the coefficient of friction which varied between 0.18 and

0.30. In that study the horizontal input acceleration was about 80% of the actual earthquake record

(i.e., the Pacoima Dam s74w component of the 1971 earthquake accelerogram) applied simultaneously

with various levels of the vertical component Time histories of the block displacement relative to the

table, given in [11), show \:xtrernely lar~,e end-of-signal offsets that reveal the need for a recentering

spring.

3. Accelerations

One of the main purposes of base isolation is the reduction of ground accelerations transmitted to

the structure. The acceleration r~duction is expected to improve with softer systems like the ones

consisting of rubber only. By the addition of sliders, the accelerations in the structure were slighlly

higher than the ones corresponding to a solely rubber system. The peak base acceleration to peak

ground acceleration ratio increased from an average of 0.5 for the system using elastomeric pads, under

input spans around ISO, to an average value of 0.9 for the system that included sliders, for input spans

as high as 375. As shown in Table T-?l, the i&oIated base acceleration amplification ratio Was highest

for the Mexico City signal (about 1.7) and lowest for the San Francisco signal (about 0.6), because

high frcqucnq signals induced more sliding causing a softer equivalent system. Intermediate values

-93-

were found for most of the other earthquakes which had their inpul energy spread over a wider range

of frequencies. Thus, there was almOSI no reduclion in the ground accelerations, and the accelerations

in the top stories were oflen slightly higher than the table accelerations for certain signals at low spans.

However, Ihe concept of isolation was still preserved. since for the fixed base case, these amplification

ralios reached 4 or 5 for input spans of around 100. Figures 7.20-7.27 show acceleration time histories

for ii)~ table and the fourth and ninth stories normalized to the peaIc table acceleration, for the fixed

base structure and for the structure isolaled on Ihe combined system. They illustrate the reduction in

accelerations provided by the combined rubber-sliders system. When the structure was tested as fixed

base, the peak ninth story acceleration to the peak table acceleration reached 4.39 for EI Centro input

125 span. 5.28 for Parkfield input 125 span, and was between ].6 and 3 for the olher records at similar

spans, while for the isolated base case these ratios did not exceed 2.2. These values are summarized in

Table T-7.3. Plots of the acceleration amplification along the elevation of the structure are shown in

Figure 7.28 for the fixed base case and in Figure 7.29 for the base isolated case.

4. Effect of Input Magnitude

The effect of the magnitude of ground displacement on the acceleration and displacement model

response was examined by using the EI Centro record belween 150 and 425 horizontal spans. II was

nOliced lhat the peak base relative displacement to the peak table displacement ratio increased with the

span of the input up to a certain span level (around 300). After this level, the ratio started decreasing.

The increase in the displacement amplification ratio for spans below 300 was due to the increased

participation of the rubber bearings. At a horizontal span of about 300, the tension devices came close

to locking and caused an increase in the stiffness, and hence a decrease in the base displacement

(Figure 7.30). figure 7.31 shows the hysteresis loops of the north bearings for horizontal spans of

ISO, 300 and 400. The effect of the restrainers can be seen for the 400 horizontal span. The same

conclusion was drawn for the ninth story relative displacement Generally, the displacement

amplification ratio for the base was between 0.5 and 1.0 for all spans, and for the ninth story was

between 0.9 and 1.5.

-94-

The amplification ratios for the accelerations generally decreased with increased span. However,

the lowest value was for a horizontal span between 300 and 350, because of the stiffening caused by

the restrainers close to locking. It is thus shown that the more the system is activated the lower the

acceleration amplification ratio. These factors are summarized in Table T·7.4 and plotted in Figure

7.30, which shows the presence of an optimum span where the system provides the largest reduction in

the accelerations.

If the building under consideration is expected to house equipment, sensitive to high frequencies

and high accelerations, the proportion of sliders in the isolation system should be kept lower.

However, if good isolation is required as well as reduction in the displacements, a high proportion of

sliders can be used.

s. Rue Sbear

Since there were no instruments installed in the frame to measure member forces, the interstory

shears were obtained by determining the inertia forces at each level. This is accurate enough for steel

struetur~ that are still in their linear elastic range, because they have very low damping, and the elastic

force would practically equal the inertia force at each level.

The only check point between the statics and the inertia method was the base level, where the

load cells for force measurement were installed. The limiting value FIIlU for the base: shear was

expected to be greatly influenced by the 4;OCffu:ient of friction of the sliders, since for a given

displacement the additional shear provided by the rubber is constant. Assuming that the structure is

moving as a riaid body, denoting by FIDU the maximum base shear, and by Ymu the maximum base

ICCCleration, the foUowing equation holds:

where M and W are the total mass and total weight of the structural model. However,

-95-

where I!mu is the maximum friction coefficient reached at maximum sliding velocity, F. the maximum

shear at the sliders, and a the fraction of total weight carried by the teflon. Thus, if the sliders were

installed without the rubber bearing.'>, the base acceleration would have had an upper bound of

With the presence of the rubber bearings, it is increased to

(7.1)

where lImu is the maximum base displacement

Although the friction coefficient depends on the sliding velocity, I!mu can be fixed at a certain

value obtained from tests (in our case 17%), and thus the maximum base acceleration corresponding to

rigid body consideration of the structure is controlled by an appropriate combination of the two

parameters a and Kr.

It was noticed that the frequency content of the different earthquakes is reflected in the accuracy

of this approximation. The higher the frequency content of the earthquake is, the larger is the

difference between the measured base shear and the one obtained from rigid body considerations.

6. Energy Dissipation Emdenq

It is commonly accepted that the total energy transmitted from the ground to a structure is

absorbed in two different ways. The first one is due to the elastic strain, the second one is due to the

plastic strain. The elastic strain energy is temporarily absorbed by the structure, part of it is

transmitted back to the soil through the foundations and the other part released as kinetic energy

causing amplification in the response quantities. For this reason, conventional design has a tendency to

dissipate the major amount of the total energy absorbed by means of inelastic behavior of structural

and non-structural elements. The need to increase the dissipated energy is satisfied by the use of

sliders. It is shown here that the major portion of the total energy absorbed was dissipated by friction,

minimizing the amplification in the response, and concentrating the deformations at the isolation

-96-

interface.

The efficiency of the combined rubber-sliders system in dissipating energy was investigated by

examining the load-deftection relationship at the isolation interface. Hysteresis loops of total base

shear versus relative base displacement were obtained for different earthquake signals and are shown in

Figures 7.32-7.35. The total energy dissipated was calculated by numerical integration of the areas

enclosed in these loops while the total input energy was obtained by integrating the product of the base

shear with the table displacement time histories. Figures 7.36-7.43 show the cycles of energy

dissipation (top). the cumulative input energy and the cumulative dissipated energy time histories

(bottom). The proportion of the total input energy dissipated by hysteresis was above 90% for all

eight tablt motions used. Table T-7.S summarizes the results. It should be noted however that

because of instrumentation resolution and beause of numerical errors these values are valid to ::t5%.

Nevertheless. these plots show the efficiency of concentrating the energy dissipation at the isolation

interface.

In an attempt to evaluate an equivalent damping. the total energy E dissipated for each test run,

was divided by an estimated number of significant cycles N, read from the base drift time histories and

from the instantaneous energy dissipation plots. Thus, rod. EIN provides an average value of energy

dissipated per cycle. In order to determine an equivalent elastic work, ro., it was assumed that

w•• F"l,,,j2 where FII is tbe maximum base shear and 611 the maximum base relative displacement

An equivalent damping ratio was then evaluated by ~. ro"'4Kc.u.. The values of £, N, and ~ are

presented in Table T-7.6 for the eight earthqualce records used. The values of ~ wcre about 20'17 for

all sipals.

·97-

Table T·'.1 Peak values or b~ and ninth story response (top), with their correspondln&ampllftcatlon ratios (bottom).

- Table Due Ninth .tory

filename Dm..(in. ) Am.Jg) Dma>(in. ) A max(g) Dma.(in. } A m..(g)

861119.03 ELC3i5 1.96 0.73 1.36 0.43 2.01 0.64

861119.04 MEX3i5 1.97 0.18 1.91 0.31 2.55 0.39

861119.05 BUC300 1.56 0.27 1.27 0.32 },75 0.31

861110.06 MIY350 1.81 0.33 1.22 0.38 1.72 0.46

861119.07 PAC350 1.82 0.49 1.30 0.52 1.87 0.59

861119.08 PAR350 1.82 0.41 1.09 0.37 1.46 0.46

861119.09 SFR200 1.01 1.~0 0.84 0.68 1.23 0.63

861119.10 TAf'350 1.83 0.72 1.36 0.39 1.62 0.68

- Acceleration Amplification Displacement Amplification

filenameA b",. Aft",r~ Aftiftlh D..... DRiftlA DRlftrh-- --

DrG". DIG.,. D.....A IG'/r A ,Gbl, A ......

861119.03 ELC375 0.59 0.88 1.49 0.69 1.03 1.48

861119.04 MEX375 1.72 2.17 1.26 0.97 1.29 1.34

861119.05 Bl'C300 1.19 1.15 0.97 0.81 1.12 1.38

861119.06 MIY350 1.15 1.39 1.21 0.67 0.95 1.41

861119.07 PAC350 1.06 1.20 1.13 0.71 1.03 1.44

861119.08 PAR3aO 0.90 1.12 1.24 0.60 0.80 1.34

861119.09 SFR200 0.57 0.53 0.93 0.83 1.22 1.46

861119.10 TAF350 0.54 0.94 1.74 0.74 0.89 1.19

-98-

Table T.7.2 Base displacement end.or.signal offsets ror ti&htearthquake records with their corresponding peaktable displacement and peak table acceleration.

filpnam.. si(l;nal B8.<;(' OfTspl (in.) PTD (in.) PTA (g)

861119.m ELC375 -0.061 1.96 0.73

861 I IQ.01 MEX37a 0.212 1.97 0.18

861 I 19.0a Bt 1C300 -0.006 1.56 0.27

8611 UI.06 MIY350 0.119 1.81 0.33

861119.07 PAC350 -0.025 1.82 0.49

861119.01' PAR350 -0.011 1.82 0.41

861 119.09 SFR200 0.037 1.01 1.20

861119.10 TAF350 0.057 1.83 0.72

Table T·7.3 Atcelentlon ampllftcatlon ratios at fourth and ninth stories for ftxed baseand base Isolated stnlcture.

FIXED BASE STRUCTURE BASE ISOLATED STRUCTURE

signal PTA (g) 4th swry 9th story signal PTA (g) 4th swry 9th stor)'

ELCI25 O.2!) 2.53 4.39 ELC375 o.n 0.42 0.88

MEX.OO 0.06 I.G5 2.44 MEX375 0.18 !.G4 2.'7

DUCI75 0.17 1.41 2.53 BUC300 0.27 0.70 l.JS

MIYI50 0.16 2.05 3.00 MIY350 0.33 0.63 1.39

PACI25 0.1~ 1.02 1.66 PAC3f)() 0.411 0.45 1.20

PAR.25 0.14 3.30 5.28 PAR3.',O 0.41 0.53 l.J2

SFRloo 0.73 0.94 I.~ SFR200 1.20 0.23 O.~

TAFloo 0.20 1.{)2 2.2& TAF350 0.72 0.38 0.94

-99-

Table T·7.4 Peak values of base and ninth story response (top), wltb their c:orrespondhqamplification ratios (bottom). for EI Centro record with increasmg SpaD.

. Table Due Ninth .tory

filename Dmu(in. ) A 010'(') D 010'( in. ) Amat,(') D mat,( in. ) A mo,(' )

861117.01 ELC150 0.78 0.27 0.49 0.19 0.75 0.31

861117.02 ELC200 1.04 0.39 0.76 0.21 1.04 0.38

861117.03 ELC300 1.56 0.58 1.41 0.29 1.92 0.48

861117.04 ELC350 1.83 0.68 1.53 0.35 2.14 0.55

861117.05 ELC400 2.07 0.80 1.71 0.41 2.33 0.64

861117.06 ELC425 2.22 0.85 1.82 0.48 2.50 0.67

- Acceleration Ampli!1cation Displacement Amplification

filenameA.GO, A"i"th A"'flth D.GO, Drai"tI. D"i"lhAlattr Alablr A...., DIG'" Dld1r D,GO,

861117.01 ELC150 0.70 1.15 1.t:3 0.63 0.96 1.53

861117.02 ELC200 0.54 0.97 1.81 0.73 1.00 1.37

861117.03 ELC300 0.50 0.83 l.e6 0.90 1.23 1.36

861117.04 ELC350 0.51 0.81 1.57 0.84 1.17 1.40

861117.05 ELC400 0.51 0.80 1.56 0.83 1.13 1.36

861117.06 ELC425 0.56 0.79 1.39 0.82 1.13 1.37

-100-

Table T·75 Eneref dissipation efficiency of the combinedrubber-sliden isolation system.

li,;nal Input Enerl)' (£1 ) Dissipated Enerl)' (Eo)EoE1

ELC375 221.1 205.4 93%

MEX37l> 246.5 250.8 102%

BUC300 56.0 M.6 97%

MIY350 166.2 157.5 95%

PAC350 75.5 72.3 96%

PAR350 44.6 41.9 9-1%

SFR200 3B.7 34.9 90%

TAF350 146.3 137.2 94%

Table T·7.' Equlnlent ciampini and equivalent ItUl'nn. obtained from experimentalhysteresis loops of base shear for e1aht rec:ordL ~ around 20.,.

filename signal E N E -0 K (k' -I)-0 =- IUS (~t = -4-(%) ~II .IftN Wttls

861111.03 EI,C375 205.3B 6 34.23 13.6 20 15.0

861111.04 MEX375 250.79 5 50.16 20.1 20 11.8

861111.05 BUC300 54.55 2 27.28 10.4 21 13.0

861119.06 MIY350 157.44 5 31.49 11.3 22 15.1

861111.07 PAC350 72.33 3 24.11 11.2 17 13.6

861119.08 PAR350 4J.13 2 20.07 8.3 20 14.7

861111.09 SFR200 34.10 2 17.45 5.7 24 16.6

861119.10 TAF350 137.23 4 34.31 12.4 22 13.6

Aver.. 21 14.2

MRPRA SET #1 SYSTEM RUDDER·SLIDERS SYSTEM

I I

-3 U·ij·V.Jjlo"t'J~,.. I I,J~\~~' .AI I;::l

-~--

~J,,~ I IA....It~ .. /;....~

! I ~. I II I~

Hl-~..

I [~-':~=~=J ~.-0-.

- -""""""'"-- - -----,~

1!~.,..kh~tf."~1"". A I I~\irVVtN.I'IIA.IJ~)~I~J~....... I~, ,

0 5 10 15 20 0 S 10 15 20

Frequency (HI.) Frequency (H••)

F...."7.1 Acceleration Fourier transforms for [I Centro record span 200.

MRPRA SET *1 SYSTEM

-II I J~'\..o.."",,=- _ I='~~Go

~

!1~Jt·· I~..JilL oh . .-l

l~-d>~"" I I

RUBBER-SLIDERS SYSTEM

c..:r

e-

I~~ ,;I'""" On • ,

w...0.

~=".k,,'" I~I ~

l~ ~~~~_M ~I

....Q

t;'"

o 5 10 15 20 o 5 10 15 20

Frequency (liz.) Frequency (HI.)

Figure 7.2 Acceleration Fourier transfonns for Bucharest record span 250.

-8::II

t~ii..I~

."

"..:;e..~

MRPRA SET # I SYSTEM

_.

A~

1

,l

J..

J

RUBBER·SLIDERS SYSTEM

J :.';'(>~

IJ·~

t

L o ""~"""HtMt.....

~ilt...N...

f

CI~

~

01~

~

c.-..Q.

,

ta....Q

>\,HI

r.ntr:l

~c-r-1

Q 5 10 15 20 o 5 10 15 20

Frequency (lb.) Frequency (117..)

Figure 7.3 Acceleration Fourier transfonns for Mexico City record span SO (left)and span ISO (right).

BASE SHEAR HYSTERESIS LOOP

MRPRA SET'1 SYSTEM RUBBER-SLIDERS SYSTEM

15

10

J s~-a::.: 0(11

=eft -s

-10

-11-3 -) -I 0 1 2

DlIlplacement (in.)

15

10

S

k1 0P•

-5

-10

-153 -3 -a -1 0 1

m.placement (in.)

3 3

I-~

Figure 7.4 Base shear hysteresis loop for El Centro record span 200.


MRPnA SET." 1 SYSTEM RUDDER-SLIDERS SYSTEM

.oVI,

32-1 0 1

Di.placement (In.)

-2

~if

~

r

V

5

-s

15

10

-15

-3

-10

k1 0P•

15

10

-.e. 5~-~

< 0W

=fI) -5

-10

-15 ------

-3 -2 -1 0 1 2 3

Diaplacement (in.)

Figun 7.5 Base shear hysteresis loop for Bucharest record span 250.


MRPRA SET *1 SYSTEM RUBBER-SLIDERS SYSTEM

....i.

0.30.2-0.1 0.0 0.1

Di.placement (in.)

-o.a

10

5

-5

k Hftfll1 0 Ip•

-10 r- I I I I I !

0.3 -0.3o.a-0.1 0.0 0.1

Displacement (In.)

-0.2

.-..~

l- I I I

-0.3

10

-10

- 5

.1-~-=~ 0w=fI)

-5

Figure 7.6 Base shear hysteresis loop for Mexico City record span SO (left) and 150 (right).

DEFLECTED SHAPEAT MAXIMUM RELATIVE DISPLACEMENTS

Ft. 4 • t" 4.35 d • -1.119

·u -L5 ~ o.s 1.5 2.5

'7

6

-as -1..5 ~ o.s 1.5 as

I!llISE - t~ 3." d= 1.35

I

, I_L-J

-.5 -1.5 ~ 0.0; 1~ 45

It. 5 - e- 3.8 d = 1.91~

I I

~ I 'lI I~I

I V~--'-u -1.5 -G5 U 1.5 as

It. 1 - t" 3. 'l8 d = VI')

9, Ii'I

1--

-45

El.6 - t= 3.ld~ 1.9S

It. 2 - t" 3.'78 d =1.S?

P4~-ffl~t-t=Tt-+m-t-{~

__ ~J~:-...l....-..J-45 1.5 ~5 05 1.5 25

n. 7 - t= 4.35 d = -2.06-j

-,II

,\ I

"-as -1.5 ~5 o.s 1.5 2.5

n. 3 - t= 3.'IBd - 1.6'1.J l

E I

1

...--2.5 -1.5 -o.s 0.5 1.5 1S

n. II - too 4.34 d ~ -1. 0lL5

!

~ L-\

-~,

-25 -L5 ~ 0.5 1.5 U

FL 9 - ta 3.79 d • 2.01

v'U -1.5 -o.s o.s 1.5 as

I-o";-I

FalUre 7.7 Deflected shape rf structure on rubber-sllden system, at maximum storydisplacements far El Centro signal 375 span.


-as -1.5 ~5 05 1.S ')...,

-2.5 -1.5 ~ os 1.5 as

n.. - ~ 2O.9d ~2.&

I-~

FL .. - t= 20.9 d = 2.47

n. 9 • ~ 21.'l8 d ~ 2.SS

-15 -L5 -0.5 0.5 1.5 1S

·2.5 L5 0.5 0.5 1.!i 2.:>

I Jg

,~

"-

1

iI l.--

- -ilI u

lie-

t-

-I ~r-

I

'-'t- I--- I---

4

t- lI ~' __ Jl...-L._ .

FL II - ~ 21.911 d ,. 2.411

n. 3 - to' 21."d~ 2.2

2.5 ·1.5 ~.5 0.5 15 2.5

-2.5 -1.5 ~ 0.5 1.5 25

tI

l----~f--

ll

~

"'I

,1

)--....k::::!-:-+::--~

no 2 '~O' 21." d -" 2.U

no 7 - ~ 20.ll'lI cI = 2.65

·2.515 ~ C.5 L5 ;'.5

-as

-r----T-,~ 1"1 j J"

~

r--

I-- I---

-1--t--

U~_LLl.JJ

t- r--T- rr-- °l

J$~t-+~jj~

tGl$6

n. 1 • ~ 21.'77 d • 2.0'1

9

7

-j

2 +1

-~l

l... _1_

9'lr=r_=~~~- .

I-1

j

lINE • ~ 21.9'7 dO' 1.91

n. 5 • ~ 20.89 d ~ 2."

!L

.I

~

I

,.-J

·15 -L5 0.5 05 1.5 25

-15 -i.5 ~.5 OS 1.5 z.5

.

I~

li

V

Figure 7.8 Deflected shape of structure on rubber-sliders system, at maximum storydisplacements for Mexico City signal 375 span.

DEFLECTED SHAPEAT MAXI~1UM RELATIVE DISPLACEMENTS

ME - ~ 3.2'7 d= -1.2'7

-~ -1.5 ~.5 0.5 1.5 15

61

8

'7

,-~n. 9 - to' J.x. d '" -1.'15

no ... tl= 3.39 d • -1.82

-2.5 -1.5 -os 0.5 l.S 15

f't. 3 • t= 3.2'7 d " -1.411

FL 8 - t= J.x. d = -1. '7J

-2.5 -1.5 ~5 0.5 1.5 2.5

n. 2 - t= 3.26 d • -1.43

FL '1 - t= 3.29 d = -1.93

-2.5 -1.5 -OS 0.5 1.5 Z.5

n. I> • t= 3.29 d = -1.119

'15 -15 ~ o.s 1.5 15

n. 1 - t= 3.2'1 d '" -1.399

5

4

3

2

no 5 - tl= 3.39 d • -1.M

UI

l ..-a.s -1.5 -o.s Cl.$ 1.5 15

9

-15 -15 -os o.s l.S 15

lI

\

f---

L,-15 -L5 ~.s os 1.5 2.5

!'- .L

HJI

lf--t-.........

-2.5 'is -o.s 0.5 1.5 U

l-a.s -1.5 -o.s lI.5 1.5 15

Figure 7.9 Deflected shape or structure on rubber-sliders system, at maximum storydisplacements for Bucharest signal 300 span.


IlJIS! • t& 6.63 d- 1.U !to 1 • too 6.63 d. 1.31 n. 1 • too 6.64 d " 1.37 fL 3 - t" 6." d • 1." n, ... too 6.65 d • 1.62

l--J ,,.z.s -u -U ~ l.5 1S

n, 5 - tl- 6.65 d - 1.67

---.~r"f7'

6

..3

J

1

iI y'

-'%.5 -1.5 ~.5 0.5 1.5 1S

n,6 • ~ 6.65 d -1.7

- h1L-J' ~l

""-

-

-If--

j.)-'--

-25 -1.5 ~.5 o.s 1.5 Z.5

ft. 7 - t'" 6.65 d - 1. '74

"r 1III

'--

-

1

j..J'--

-Z.5 -1.5 -o.s 0.5 15 l.S

flo II - t& 6.64d· 1.67

i

~).2.5 -1.5 -05 G.5 IS 1S

n. 9 • tl- 6." d & 1.72

,--oI

t

.Vi-l.S -1.5 -05 o.s 1.5 l.S-2!. -15 -o.s 0.5 15 15

JI I 1 1

i

--! c--

-

1

1.)

I

II

I iI

,J.1S -1.5 • .5 o.s 1.5 2.5

-'r 1 15

7

&-

5

I

3

Z

l

Vi-.s -1.5 ~ 0.5 1.5 1S

..l

II

!

~!-15 -1.5 -4.5 0.5 1.5 ~

Figure 7.10 Deftected shape of structure on rubber·sliders system, at maximum storydisplacements for Miyagi.Ken.Oki signal 350 span.


.---,

n. ... C" 3.17 d .. -1.93

L

\

lLl-:z,s -1.5 -0.5 o.s 1.5 Z.5

n. 3 - t" 3.15 d .. -1. !is

-4.5 -1.5 ~.s OOS 1.5 :loS

ft. 2 • to' 3.16 d ~ -1.5

l.-.l_~.-J-z.s -1.5 ~.5 o.s 1.5 3.5

I I

L\

1

, i~ I i

.L

,6 I~

\

l

\ IL I" I

I

~~ i

7

-z.s -1.5 ~ o.s 1.5 Z.5

n. 1 - ~ :1.16 d" -1.43

'I8

4;i

3

3

1

,5

IlIIISE - t a 3.16 d~ -1.:1

\

l .. j J-~ -1.5 -0.5 o.s 1.5 Z.5

fL 5 • C" 3.la d a -1.96 ft., -~ 3.17d: -3.0:1 n. 7 - t: 3.18 d : -3.07 FL 8 - t" 3.1ft II a -1.85 FL 9 - ta 3.15 d: -1.87

-Z.5 -1.5 -4l.5 o.s 1.5 U -3':; -l.5 ~ 0.5 1.5 U

\

~1-0..~ -1.5 ., G.5 1.5 Z.5

:I

1

-15 -1.5 ~ 0.5 1.5 15

\

l-u -1.5 ~ G.5 1.5 as

FilUre 7.11 Dellected shape of structure on rubber-sliders system, at maximum storydisplacements for Pacoima Dam signal 350 span.


fL 6 - t'" 3.es d - -1.64

.~ -1.5 -U Cl5 1.5 ~

-J,S -1.5 -U Cl5 1.5 ~

.. - CO' 3••• -1.09

ll

-u -1.5 ~ o.s 1.5 ~

n.s - ~ 3." d· -1.61

l-u -1.5 ~ o.s 1.5 ~

ft. 1 - ts 3." cl- -1.19 ft. Z - t z 3.114 d • -l.U

~-J,S -L50.s Q.5 l.s U

fL 7 - t= 3.1144 = -l.Y

I

!\.

Ll

~-~ -1.5 ~.s Q.5 l.s U

n. 3 - ~ 3.M d • -1.35~ .• • I I T 1

~ -.. U -

4 --

~_J -1.1 I -I I IL III 1J

-J5 -..s ~ 05 1.5 U

FL • - to' 3.G 4 • -1."

i

\

I

i~~.

-J.5 -l.s ~ 0.5 l.s U

n,4 - co 3•• d· -1.S9

l-&5 -l.s -Cl.5 o.s 1.5 a5

FL 9 - co 3.G d • -1.46

l-&5 -l.s ~ o.s 15 a5

I--t;.J

Figure 7.12 Deflected shape of structure on rubber-sliders system, at maximum storydisplacements for Parkfield signal 350 span.


ME - ll" 2.44 cI' -0.14 Et. 1 .. tor 2.44 d a -0.91 Et. 2 - t= 2.44 oS = -0.96 n.. 3 - to' Z.43 d • -1.01 n.." . t'" 2.44 II • -1.14

tl.5 • to' 2.44 oS a -1.17

I I l! I I j.

L-L_~--L--15 -1.5 ilS ll.5 lS 15

fL 7 - '.= 2.45 oS = .1.2.3

I : ~ I I IIt 1 _:h.J-L-~ -1.5 oilS OS 1.5 2.5 .--If

n.. 9 - t" 2.44 d • -1.23

-~ -1.5 -o.s ll.5 LoS Z5

fL a - t= 2.44 d a -1.2

-25 -1.5 il5 0.5 1.5 z.s

•~

I

. I I

1 L~ I lL I 'hI

fL 6 to' 2.44 oS a -l.Z

-z.s -1.5 ~.5 CS 1.5 z.s

9

A L I71_ L

I

6

5

4

2

1I

f \ I

~I

--'I

, ,

~-:u -1.5 -G.5 0.5 1.5 15

OJ

II

7

6

4- l.3

Z

1

l~-15 ·1.5 ~ o.s 1.5 15

~

4-,

l ,.-15 -1.5 11.5 o.s l.5 2.5

~IL

I

I-

Lr--...

-.l.5 -l.5 -G.5 o.s l.5 a.s

l'i'-o..l

-a.s -l.5 -o.li U 1.5 Z5

Figure 7.13 Deflected shape of structure on rubber-sliders system, at maximum storydisplacements for San Francisco :signal 200 span.


-1S -1.5 ~ o.s 1.S 15 ~ -1.5 ~ o.s 1.5 15 -2.5 -1.5 "0.5 0.5 1.5 as

..... t" S.... -1.36

-..........

""-1!> -15 o.s o.!> 1.5 15

n. 5 - tK 5.16 d ~ -1.73

It. 1 - t;o 5.08 d. -1.44

I

7

6

2

1

..........15 -1~ ~ u.s U 15

ft. • - t" 5.16 d" -1.75

n. 2 - t= 5.08 II • -1.415

I'

~f---

1

"........."

-15 -,j.!> ~s 0.5 1.5 2.5

ft. 7 - t= 5.16 d • -1.18

I

L,-15 -L5 ~.5 o.s 1.5 2.5

FL 3 - t" 5." II ,. -1.47A

J

t

I "'........-2.5 -~ ~"5 0.5 1.5 15

fL 1- t" 5.lS d ~ -1.61

fL 4 - tK 5.16 d • -1.72

L" ""-2.!> -1.5 ~ o.s 1.5 15

fL 9 - tK 5.lS II ., -1.62

l"~"-as -1.5 ~ 1.5 1.5 15

.--~

Figure 7.14 Deftected shape of structure on rubber-sliders system, at maximum storydisplacements for Tart signal 350 span.

FIXED DASE ISOLATED ON RUBDF.R-SLIDERS SYSTEM... ~~--~---~------~--_.~ 0.. · -- . ---~.- -- .. -

OGlJ oIf> I ~

0.0'-1-"-""A'j\,"'~"--- "['V;\i~~\;f\{V'v~~_~ __ I ~

0<

"":' -~ J • • • »----ta.... • J • ;. -. » IJ.!-fot ... 0.11

~: J,~v..,.....·: -.p • : ~~~ ,

>- -L -- -<::~ ~

~ ""0 -;---. 6 • III IJ -G.ID, J :. 6 • II IJ

•OJD

1

------ ---- ------ -- --~ 0.11- --- -- -~ -- w

~~~~~~~~ i• J • • • II IJ • J • • • II IJ

time (1IeC.) time (1IeC.)

Figure 7.15 Story drift time history for San Francisco record at 100 horizontal span(PTA~O.7g, left) and 200 horizontal span (PTA=1.2g, right).

.........tr'

3530252015105o

2

2r - - ---

:t' ,..."I\!l....AAh~I~~fir--_IVV - ~

-2 ~- ~-'

-2' • --.J

o 5 10 15 20 25 30 35

::~'~~~~~~~IHPIlII'" I-11 ~ V Vr ~

~o

20

15

15

10

10

5

5

~..----- -~-------

OI f1A I I( t -"'.JV\J'::wl. .1"'\ _rl k I_i G ,,~,..

~

o f------r--.l-'\-f-l I 11 '\ ~

1

1

-I

-~ rL..- ~ ~ ~

o

-I

_ ~ L • I

o

-.!-f'a

~fo4

-.!-,...'a

J

5

I j----------

353015 20 25time (1IeC.)

10

- 0.1I

o.2L __~20 0IS10

time (1IeC.)5

0.8-~ 0.6U 0.4u o.~

~ o. 0 I .-JII,2-0.2.. -0.4

fo4_ 0 . 6-0.8

o

Figure 7.16 Top 6gure showing base drift final otTset, EI Centro 375 base otTset-·O.06 in.Off'l), Mexico City 375 base otTset=0.21 In. (right).

"":" 2.9-~

1..0~

I -1eQ

-20 2

2-- ------_.

.e-.. 1Ii.

.S0..,

J!A -1's

Eo- -21.0 2

-1 2 f~ - - ~- - -- -- ~ -- -- - ~- -~ I

I I

~~~~~~ j :1. --JlvM~~=_____ .£_ ...... Lo-- ...... ........

4 & 8 10 12 0 2 4 & 8 10 12

2 r---- ----

WJ~~---~I

1

°r---~

-1 r V

V ~____~_J .--2L__~__ -....-~----~---

.4 & 8 10 12 0 2 4 & 8 10 12

_ 0.3 0.4 - --------

.!! 0.2 0.3

r~~fV~~~u )~ I'~V' ~ Iy~' 4

I.. •

0.2'" 0.1 0.1~ 0.0J! 0.0 -1 ,y ifJrt f ~'fr, 'I

-0.11-0 . 1 ~ ,In -0.2~-0.2 -0.3

-0.3 -0.40 2 4 & 8 10 12 0 2 4 & 8 10 12

time (eec:.) time (eec:.)

Figure 7.17 Top figure showing base drift final offsel, Bucharesl 300 base ofTset• .o.OO6 in.OeR), Mi~·agl-Ken·Oki 350 base olTset=0.19 In. (right).

- If I 2

.!- 1 1,j 4f'=.. 0

"J -1

-l -2

0 2 4 6 8 10 12 0 2 4 6 8 10 12 14

- 2f 1 2Iic 11 J I J \ I 1.t

01 .< I J ,I" 'CII: :> , < :=:>< 7' 0

J!,Q

~:tvv

.1 ~:[ .1

.~ --00

I.0 2 4 (, 8 10 12 0 2 4 6 8 10 12 14

_ 0.6 0.3..!! 0.4 0.2

V

I,~~ - 0.1" 0.2 0.0~J! 0.0 -0.1

1-0 . 2 -0.2~ • PO

-0.3fol-O.4 -0.4

-0.6 -0.50 2 4 6 8 10 12 0 2 4 6 8 10 12 14

time (1IeC.) time (8eC.)

Figure 7.18 Top ftgure showing base drift linaJ offset, Pacoima Dam 350 base oll'set--o.025 in.(left), Parkfield 350 base offset.·O.041 In. (right).

""':' 2r-----·_-- - -------------.

2f-- --- --- -- --- ---- ----- -----

.5 i- I

t! 1 1

~~.'~~=j.- II..

0-a 0

VI -1 -1

= -2 -2

0 2 4 6 8 10 12 14 0 5 10 15 20

- -------Ii 21 I 2--ci. If "- I 1.1-a

J :v: ~~ I

0.! .A

~:LVVV'- I .-• -fool I 'P

0 2 4 6 8 10 12 14 0 5 10 15 20

Ii 1.5f I 0.8~ 1.0 0.6

~ 0.5 I' I ~ : ~ r 'tl~ 11.1. ,

. I J~I ·'~.rl;·~~~~-1.51....- ----.-._--~ -0.8' :

o 2 4 6. 8{ ) 10 12 14 0 S 10) 15 20time Re. time (Re.

Figure 7.19 Top ftgure showing base drift ftnal offset, San Francisco 200 base offset-O.037 In.(left), Taft 350 base ofTset:O.057 in. (right).

FIXED BASE ISOLATED ON RUBBER·SLIDERS SYSTEM

:1 II... I : ~I ~

~ :1 1"". 111"''', • I: ~-< I , • a a IS. IS a

~~ . .~ . .~ ~ I il ~ ~ -_.... " ~ Ii ~Q(IJ .~ ~ it a a· I , • IS aN-~ 1 I •~ . .::.0=:/-*... .... 'M" ...... ' .~, 1:/ .... '11 ...... 'J .. '.. I~ilV • tV,.,.x" 41 ,.,. i . -,v. , , taZ .. ., (;j

4 4

.' t • • I.IS. IS • IS. IS a

time (Ree.) tim~ (....r.l

Figure 7.20 Accelention Time histories normalized to peak table acceleration for EI Centrorecord 125 horizontal span (PTA=O.2Sg, len) and 375 horizontal span(PTA=O.73,. right).

FIXED BASE ISOLATED ON RUBBER-SLIDERS SYSTEMJ

I.1c..:r

Z 'I.~•

I~~

~ : -I

...=-I. I • II a • • • • , • D a a • •r.:I..Jr.:Ito) J , ....to) 1 I :r< III• • ~

0 ,0

1 -t ::0 -N00( -r.:I I -J I

N .1 -I- • I .. 15 a ZI • ~ • I 10 I' a • • •..J

<~II ,c: J

01 11 ~

z • ;, i;f-a ~

-I , .JI .D

. , • ·1

• , • a • • • , • D a • • •time (..c.) time (Bee.)

Figure 7.21 Accelention time histories normalized to peak table accelention for Mexico Cityrecord 100 horizontal span (PTA-O.06g, left) and 375 horizontal span(PTA-O.18g, right).

FIXED BASE ISOLATED ON RUBBER.SLIDERS SYSTEMJ, i J

I IC)..:rrn

Z • ~00 I ::tl- 0<

f-e .,-< .Jl J .). .~ • , • .. • • II • • J • • • • " •l&I~

~I)

l&I

I0

~I•...

0« Aft~UAAOO,1o .

:rCIJ< ~'l""".JrI. ~v ,yvtrll rt 0 .

:1". 'I"'

,

J

:::0 -NQ 0< ~

l&I.J

N . . . -J- • J 4 • • II II • 0 J 4 • • • II •~

-< ),i J

::E~

0 I

:1~'''''+M.tA; · I

~

z • ~roo

t trJ., ,) J

• , 4 • • II IJ • • J • • • • IJ •time (eee.) time (lM!c.)

Figure 7.11 Acceleration time histories nonnalized to peak table acceleration for Bucharestrecord 175 horizontal span (PTA=O.17g, left) and 300 horizontal span(PTA=O.27g, right).

FIXED BASE ISOLATED ON RUBBER-SLIDERS SYSTEMI, I

I...'f

co...~

III~o:=-<

•...~

en~o:=-<

... 0 , 0 0 , ,

• • • • I • U

"n. ,. I A• • • • • » u

..

..

.~

..

..

'1 ,NII'Hi

,

:z0"-..~

4' I ,', ,A-<. I • • I • U

=~..;I I

f&l I

oo-< '1 ..'''.,'I:oAIl-a11l

..Q 'I

f&l on I " ,JN' I 4 • • • u-...:I-< I

~ I

D:: ,oZ ..

..

3, I

I

I

II • ~ H~' (!H~' L. 'V'~ ~f'P\"'" I'9i~rdZ; ({4Y~ '" f~r,....

..:j

~r0t"

-JL ••• ,• I • • • • U

time (eee.l

.~.. t. J• , • • • • u

time (~,l

Figure 7.23 Acceleration time histories normalized to peak table acceleration for Miyagi-KeDOld record 150 horizontal span (PTA=0.16g, left) and 350 horizoDtal SpaD(PTA=0.33g, right).

FIXED BASEJ, •

ISOLATED ON RUBBER-SLIDERS SYSTEM

'1 .. ~~"Iz0"-...< -I~ • • i i it ~CdW~ ., i

Wto) 1

U< '1 t A" '.fllli

C"WN -I' , •. ,

• J • • • • u

'I ..... aJ\flll

i

·H ' •. "• I • • • • D

., •• eA'\:IF\~'••• • I

i

-i. . .. I

• J " • • • u

C),..:rIII.-to::0-<

.....:rfIlI"io:::ato(

I...~

.J

<~ J

c:=oz ., -..II.~JI!!

"-I. .. ,

• J • • • » »time (lK'C.)

" ~J'~~a

"~~ , " ~ • m t

time (we,)

I"i,r-ol'1

Figure 7.24 Acceleration time histories normalized to peak table acceleration for PacoimaDam record 125 horizontal span (PTA=0.18g, left) and 350 horizontal spaD(PIA=0.49g, right).

FIXED BASE ISOLATED ON RUBBER-SLIDERS SYSTEM

• ••

~I Ii,

z •&~M""-"-" t'~"- ........ •• rt~.. ·r"1'

0'-f-4 .. -4

~ .~t , . . . J •I • • • II .. • • I • • • • II •

~

{I:I • •,.,;j

{I:I •

~I Iio I

0~ . ~",............ .. ..

,-I~

Q .. ..(iI ., . .

i, . J •N • I • • • .. .. • I .. • • • II •-~

~ . •~ .. ..~ I

:1 I~0 .• .a _I"Z • iv •

'".... ..• •• I .. • • .. .. .. • , • • • • • •time (Re.) time (eec.l

F1aure 7.2!1 Acceleration time histories normalized 10 peak table acceleration for Parkfieldrecord 125 horizontal span (PTA=O.14g. left) and 350 horizontal span(PTA=0.41g. right).

FIXED BASE ISOLATED ON RUBBER-SLIDERS SYSTEM

It I I

I I10..:rfA

2:1vltf..·--.. ·..·....··

:1~ .... --......... .. •

I~r ... ~.t¢1F. · ·(.1.$. fi'f"'ijV¥."~"•

...J-< ..~ . . . I . ..

I • • • • II • I • • • • ..~

W..3 IF i I

(a)

I:1 Ii~ :1 ju,., ..... eel n •••

.,.,.,..,~ . ......." . ....Q .J I ~

I

(a)

N ..L . , . , . J ..- • I • • • • :a • , • • • ~ II~

-<~ IF i ,a:

~ :, L.. . . I·1 *~. I!

:[ •

I-to

. .i • ..

• J • • .. • , • • • II II

time (11K.) time (eee.)

Figure 7.26 Acceleration time histories normalized to peak table acceleration for San Fran-cisco record 100 horizontal span (PTA=O.73g, left) and 200 horizontal span(PTA=1.20g, right).

FIXED BASE ISOLATED ON RUBBER.SLIDERS SYSTEM

" I J

I, ,C,..:r

jl ~"~ .. I;1

.~J~I~U-LU'~ l.

Il/l~v. r1 iFff',""'" 0:tI

Vi P

0<...., • • a • s • • •

~

..:I~ J

,CJ ,

~I I..

u • ..':t'

< l/l

• 1 ~""N"i"i'~Y;'M;rtN .. ' ~, 0 ....Q " ::a N

-< ";'"~ .J -2

N .J .J- • s • • a • , • • •..:I

<:E 'F I

,=1o.

:1 "rtI'''~'' \4Vl1' ,.". ~ I~

z • ~ro.. t".. ..

of .J

• , • • • • s • • atime (Bee.) time (Bee.)

Figure 7.27 Acceleration time histories normalized to peak table acceleration for Taft record100 horizontal span (PTA=O.20g, left) and 350 horizontal span (PTA=0.71g, righO.

ACCELERATIONAMPLIFICATION RATIOS

IU: !I'.... 175 - ""'" Tabl..- 0.1 n q MIY SP1H 150 _ T~l...- a"l.~ 9 I'IIC !I'l\N I Z; _ Tel.... 0.185"

~~~-l---J./'

~vr-~--+-+-----~---l ~ 4 S 6

,...~

1 • S 6' 7

J • S 6 7

J

l

W !I'l\N 100 _ Tel.... O.lOl"

o

o 1

--- r-- ~ - T ---. '-' --- -.I'

/

,Ii

1>-L.

J • S 6 7

!J1l Sl'JIff 100 ""-k rei.... O.?lf> 9

o

o

i~-- - .-~-- - -.. --

f.-

f

1M4--\'---

~ _.-

----------- -

7

.,

-17

~ • 5 6

- ~- - ---- - ---- - ----

l

I

Pl'Il. !I'.... 125 - ""'" Tabl.... a.ll? 9

lj·._~ _-- _i__~ _-~-

o

o

J..r-

Figure 7.28 ACCl:Il:ration amplification I"atios along ele\"ation of fixed basl: structure forBucharest (PTA=O.17g), MiJagi·Kl:n-Oki (PTA=O.16g). Pacoima (PTA=O.18g).Parkfield (PTA=O.l~g). San Francisco (PTA=O.73g), and Taft (PTA=O.20g), inputmotions.

ACCELERATIONAMPLIFICATION RATIOS

,-~

I'l\C S'Nl 350 - FmIc 'nIbJp 0.466 .,

W 9'l\H 350 • IWk nblF O. 'lO4 9,I,

II\\.\

~'- .......

0.11 0,2; o.!II 0:& UIl 1.Z 15 L'5 2.1Il ~ 1S

/V

JI

'\1 \.

\~--._-

O.ll O,z; o.!II o.or. l.OD 1.Z 15 1.'5 .&1Il ~ 1S

I'l[r SFlIH 350 - PiBM Tmlor- 0.314 .,

y

'-+--+-+-+-+---i

.9 SPNf lOO ..... TIbIF 1. lOll .,

00 0.:5 OS) 0.'" I.CD l.Zi l.!II 1.'lS 1lII 1.1> l.!l

rTP=_p.L~~ I

I I ~7i/ I

/ I

4 -_ ~~J I\ I

I I\. I

- "-__LL}-J-LJ_..L_L J

'~i-, -L J__LWo.a O.Z> AS) 0.5 l.:D l~ 1..!1 ]"'/5 1GD 1.1> l5

1M !P.... .150 - ...... Tabl. 0.401 .,

lI.C !P. 3110 - ...... 'l'ablr 0.~'?5 9

--+-~,,-'-+-"-+iJmI I I I

-0.0 US G.Sl O.~ l.tO l.Z UII L~ 1m Z.z 2.!Il

1 \

I I 1; IW_.LJ-L_.L._,J0.0 ~ 0-' 0.1> ).CD 1.21 L'rI 1.0 ~ l~ l.!II

Figure 7.29 Acceleration ampliftcation ratios along elevation of base isolated structure onrubber-sliders system for Bucharest (PTA=O.25g), Miyagi-Ken·Oki (PTA-o.3J&>,Pacoima (PTA-O.49g), Parkfield (PTA-O.41g), San Francisco (PTA-l.20g), andTaft (PTA=O.72g), Input motions.

HESI'ONSE AMI'UFI<'ATION VS. SI'AN

l,S

------.~.~ ------._-,_.

Z.O '1- [ - - - -~ I',·,k '.,~ II"'''' "',101.'-11II

___ .- I'c'ilk mh ~tf)ry ; I'c'flk 'I'll "II' I,"---- - -- --------_._-

EL CENTUO EAIlTlIQIJAKE HHO. SOO!':

.....~

<p

I I

400 4l~Y>OJOO

I I

200

, .- .- - - -.- - - _.- ...

~./. -f ~*----

.,

1S0

lO 11-_~ =~ = "~~k"IJ:L"I"1 I;l'ak TnlJll'll11,I

I . -. - - - . -..I:c'ak nt.h_story ! Prak Tahll'~i

EL <"ENTHO EAUTllqt Il\KE IlHO. SOOEI

c L'r.2--..0;.So:

" I...'"~

"'8 La ~..I~

E!::7.

0.5 t-

III

0.0 L400 42S

- .. , .. - _..-

~

c("

C

"~Q.".i .. rJ II

0.5

I

I0,0 l I I ~-----L__-,-----,-_

150 20~ 3oo:lS0

IIllriwnt.flt ~Jlnn Ilor i7.On t·al !'OJl:,"

Figure 7.30 Perfonnance of the rubber ~aring slider bearing combined s)'stem with inerusing input magnitude, under -/4 time scaled EI Centro record between ISO and 425horizontal span.

-131-

North-wrst bearing (A2) North-eut bearinl (AI)

• c:•a.•2

'i..c:- iJ. I / 1:

~ 0- ..c::.. 0

/ I 0• u:lII

..c:: ..crJ C..

-2 ..c:II0~-.-2 -1 0 1 2c:•t'i..c:- 0

!. •"i::i' c- ..c::.. 8•II I':l..c::crJ 0....

CII0!is

.J

IC

It'i..c:- c

! •"i:~ c

..c.. 8•"..c:: •fI: C....

c~-~

D.pl.cement (inch) D.pl.cement (incb)

Figure 7.31 North-west (left) and aortb-east (rilbt) rubber beariDp bysteresisloops UDder EI Ceatro 150, 300, and 400 borizoabl IpU lbo_iDastirreaiaa due to teasioa device.

COlllbined rubbcr-slidors ~y!;,-pm Comhinp-d rubher-!;Itdrrs systr.m

2o-1-2

JO I , I

20

-30 It I I I II

-20

21o-1-2

JO l I I

zo

-zo

-30 It I I I If

10 L L//U~I'IIII I I I 10

1::;-ii 0

o I I If rrllrT11J7lI-I

l.-.lN,

eo

-10 l II 11lWP? I -10

Hue drift (in.) Due drif't (in.)

Figure 7.32 Base shear hysteresis loop at isolation interface for EI Centro 375 horizontal span(PTAzO.73g, left) and Medea City 375 horizontal span (PTA=O.18g, right).

Combined rubbflr-slidcrs system Combined rubher-sllders system

30 JO

20 20

10 "-- /' I , I

!.:;

I 10

.......:ai 0 I I Bn---lJ

o I

-10 L I

I I 111I~~{lllf ~

w I -10

I.-I.<oi

If

-20 -20

2-1 0 1

Due drift (in.)~

L

-30 It I I I II

2- 1 0 1

Due drift (in.)

-30 I[ , I I II

-2

Figure 7.33 Base shear hysteresis loop at isolation interface for Bucharest 300 horizontal span(PTA=O.271, left) and Mi,lilgi.Ken·Oki 350 horizontal span (PTA:O.33g, right).

Combined ruhbr.r-~l Id~rs syst~m Comhinrd rllbbcr-~liders ~Y5tem

30 30

20 20

I....'.-.l

~

~,l)

'"I ,,~I,

~

o

10

-10-10

= I IIIi 0 I

ICD

_10

!.:;-

-20 -20

2-1 0 1

Bue drift (in.)-2

-JOlt 1 I J__ -----JJ2-2

-30 It _J_~ I I J-1 0 1

BMe drift (in.)

Figure 7.34 Base shear hysteresis loop at isolation interface for Pacoima Dam 350 horizontalspan (PTA·.:0.49gt left) and Parkfield 350 horizontal span (PTA=O.41g, right).

Combln~d r\lhh~r-~lld~r~ sy~tC'm CombinC'd ruhbp.r-~lldp.rs sy~t~m

~-I/

1J~

~V\.

Ir I

.wIf'

21o

Due drift (in.)

-1

30 [ i I

o I I I I I

20

10

-30 It- I I I II

-2

-10

-20

21oDue drif't. (in.)

-1-2

20

30

-20

-30

10

-!.~-..II

0II.c:•I

a:I

-10

FllUn 7.35 Base shear hysteresis loop at isolation interface for San Francisco 200 horizontalspan (PTA=I.lOg, left) and Taft 350 horizontal span (PTA=O.7lg, right).

ENERGY DISSIPATEDAT ISOLATION INTERFACE

instantaneous

....~

'"

201510t1JDe - seoords

5

• in 1.2 r •~ 1.0

? 0.80.6

0.4ki 0.2

t' 0.0 I -lull Ii -0.2n 0

•ner9y 16

cUlDulative

---~===:::::::::::;~:::::...:=-----

01. e.J. . • I

kit'in

80

o 5 10t1JDe - !!IIl!ClDnts

15 20

Total Enerqy Dissipated = 205.38 kip· inchesTotal Input Energy = 221.1 klp·inches

Figure 7.36 Energy dissipation at isolation interface for "4 time scaled EI Centro record at375 horizontal span (PTA=O.73g).

ENERCY DISSIPATEDAT ISOLATION INTERfACE

instantaneousen "°1-er 0.89Y 0.6

0.4k 0.21t' 0.0

1 -0.2n

0 5 10 15 20 25 30 35time - !!IeCOI"ds

I....~

";-I

cumulativeen :zB(er9 2lCY

14C

ki 70

t' I J"i 0n 0 S 10 15 20 2S JO 35

time - lIIICDrds

Total Energy Dissipated • 250.79 kip·inche.Total Input Energy = 246.5 kip·inche.

Fipfe 7.37 Energy dissipation at isolation interface for -14 time scaled Mexico City record at375 horilontal span (PTA=O.18g).


instantaneousen 0.8er 0.69Y 0.4

k0.2

i 0.0~i -0.2n

0 2 4 6 e 10 12time - secon:is

I....~

qocumulative

en 75'erq

50~ --~ ~-=y-

k :Li~i .n 0 2 4 6 e 10 12

t 1Jne - !IeOllr1ds

Total Ener~ Dissipated = 54.55 kip· inchesTotal nput Energy. 56 kip· inches

Figure 7.38 Energy dissipation at isolation interface for v'4 time scaled Bucharest record at300 horizontal span (PTA=O.27g).

ENERGY DISSIPATEDAT ISOL~TTON INTERfACE

instantan~ous

.....'P

121086time - secords

42o

1. 0 ,..------~--- -~--~--

0.8

0.4

k 0.21

~ 0.0 . I1 -0.2 I , .n

ener9y 0.6

cumulative

u1084 6tu. - seoords

Total Energy Dissipated. 157.45 klp*tnchesTotal Input Energy: 166.2 kip*lnches

2

01 . p , . Io

90

ene 18r9y

k1

f1n

Figure 7.39 Energy dissipation at isolation interface for v'4 time scaled Miyagi-Ken-Oki recordat 350 horizontal span (PTA:O.33g).


instantaneouse

1.2ne 1.0r9 0.8Y

0.6

0.4k 0.21t' 0.01 -0.2n

0 2 4 6 8 10 12t1me - seoords

I-~

cumulativeen 80e

I ~~rCJy L_~

40

k1

t'1 0n

0 2 4 6 8 10 12time - !IeOtlY'ds

Total Energy Dissipated = 72.33 kip·inchesTotal Input Energy ~ 75.5 kip·inches

Figure 7.40 Energy dissipation at isolation interface for ';4 time scaled Pacoima Dam record at350 horizontal span (PTA=0.49g).

ENERGY DISSIPATEDAT ISOLATION TNTERFACE

instantaneous

• 0.7n• 0.6r9 0.5Y 0.4

0.3

k 0.21 0.1e 0.0 I . ~\,.J'l ~I 'J~IA' ."'~"'t. oil .' .. ... , .1 -0.1n

0 2 4 & 8 10 12 14t1Jne - -=rrls

,-""-,cumulative

•n SO•r9

'1 JTy

k1

~1 0n 0 2 4 6 8 10 12 14

tilDe - -.:xn:ls

Total Energy Dissipated = 41.93 kip· inchesTotal Input Energy· 44.& kip· inch••

Fipre 7.41 Energy dissipation at Isolation Interface for v4 time scaled Parkfield record at 350horizontal span (PTA=O.41g).

ENERCY DISSIPATEDAT ISOLATION INTERFACE

instantaneous

1412106 etime - seoords

42

t .Jl1lL~ '. · -"" ~

e1.%n

• 1.0r9 0.8Y

0.6

0.4k 0.%1~ 0.01 -0.%n 0

cumulative

,-~t;.J

1412104

~----~-------------------

6 8t1JDe - seoords

Total Enerqy Dissipated = 34.9 kip-inche.Total Input Energy = 38.7 kip· Inches

2

o I r~ , • I

o

40

20

ener9y

k1

~1n

Figure 7.42 Energy dissipation al isolation interface for v'4 time scaled San Francisco recordat 200 horizontal span (PTA=1.20g).


instantaneous

....•....

I

201S10t~ - secords

5

ie

0.8ne

0.6r9y

0.4

0.2k1 0.0\'1 -0.2n 0

cUlDulative

2015

~ := ~

5 10tJ_ - -.cords

Total Energy Dissipated • 137.23 kip-inch..Total Input Energy = 146.3 kip· inches

en

15'erCJy 10-k SO1\'1 0n 0

Flpre 7.43 EaeI'lD' disslpatioa lit lIoIatioD IDterfaQ for J4 time scaled Taft record at350 horizoDtai _paD (PTA-G.721>.

-144-

CHAPTER EIGIff

COMPARISON OF EARTHQUAKE SIMULATOR TEST RESULTS

WITH SEAONC TENTATIVE CODE

1. General

The Base Isolation Subcommittee of the Seismology Committee of the Structural Engineers Asso-

ciation of Northern california (SEAONq prepared a tentative code in 1986, for base-isolated struc

tures (14). This tentative code proposed two main procedures for the seismic analysis of base-isolated

slrUetures. The first approach uses simplified formulas similar to the equivalent static analysis formulas

recommended by the Uniform Building Code. The second approach uses dynamic analysis procedures

(time history and response spectra analyses). In this chapter, the values obtained from code simplified

formulas are compared with experimental results from shaking table tests.

2. Displacements

The requirement for the minimum base displacement of an isolated structure to be accommodated

by its isolation system, as recommended in the tentative code is

10ZNSTD--------B

(8.1)

where S is a soil factor, ranging from 1.0 for hard soils to 2.7 for very soft soils, T is the fundamental

period of the building obtained by considering the structure as a single degree-of-freedom oscillator,

and B is a factor related to the damping in the isolation system. The code provides tables for the

above coefficients.

ZN is interpreted as a "Design Ground Shaking" parameter. ATC 3-06 recommends a smoothed

elastic response spectrum for S % damping to be used as a basic tool for the quantitative description of

the intensity and the frequency content of the effects of local ground conditions [IS). ATC 3-06 also

sugests the better solution that consists of using four or more acceleration time histories from which

an averaae response spectrum is extracted. Botb Ipproaches are based on response spectra and do not

account for ground motion duration which is an important factor in the loss of strength of structures.

-145-

The use of base isolation provides a system that can withstand the repeated loading, thus eliminating

the concern about the loss of strength of the superstructure, if it were to be conventionalJy desipcd.

lbe intensity of "Design Ground Shaking" is represented by two parameters the Effective Peak

Acceleration (EPA), Aa, and the Effective Peak Velocity (EPV), which yields the Velocity Related

Acceleration coefficient, A". TIle EPA is obtained by averagin, the spectral accelerations between the

periods of 0.1 and 0.5 second and reducing the average by a factor of 2.5. For the one-fourth scale

steel mode) used in the present experiment, the period limits are replacc:d by 0.05 and 0.25 5CC:01Kl,

respectively. Aa is then the numerical value of EPA divided by g. The EPV is obtained by taking the

spectral velocity at 1 second period and reducing it by a factor of 2.5. Instead, the ordinate at 0.5

second is used here for comparison with the model response. A" is then obtained from EPV/30. Maps

representing the EPA and EPV for various seismic regions are available and are discussed in ATe 3-

06 1984; in the present comparison, however, the numerical procedure described above is used.

The A, and A" coefficients of the eight records used were computed for different ranges of

periods and tabulated in Table T·g.1. The response spectra of the v'4 time scaled earthquake records

used in the calculation of Aa and Av are shown in Figur~s 5.tb-5.8b.

Equation (8.1) approximates long-period displacements obtained from 5 % damped response

spectra and was developed for full scale structures. For a one-fourth scale structural model, equation

(8. t) becomes

5ZNSTD. -~-~--

B(8.2)

T is obtained from equation (8.3), using the minimum effective stiffness, Kmin, of the isolation system,

and the total weight of the structure, W:

(8.3)

In the case of the slider-bearing system, the effective stiffness depended on the base relative

displacement, which changed with the type of excitation. For the various records applied to the

system, the lowest effective stiffness was 11.8 leIin.; with a total weight of 91 Idps the effective period

-146-

would be 0.89 second. Note that the horizontal drift was limited by tension devices installed in the

corner rubber bearings, and that the maximum allowed displacement of the isolation system could be

used to obtain the lowest equivalent stiffness of the system.

The soil factor was taken as S4 • 2.7 for the Mexico City record, SI • 1.0 for the San Francisco

record, S) - 2.0 for the Bucharest record, and S2 - 1.5 for the rest of the signals.

The factor ZN in equation (8.2) was obtained from two different considerations: from recorded

peale table acceleration, and from the EPA and EPV calculations suggested in the ATe 3-06 1984

Building Code and listed in Table T-8.t. For the sake of observation different combinations were used

to determine the displacements. The D ij values were obtained using the controlling value of Aa. and

A". In order to compare the present code recommendations with the experimental results, DIII

obtained from A.1

(EPA for T j - 0.05 second and T2- 0.25 second) or A". (EPV for T- 0.5 second)

was used and the ratios D11/Dlelt are listed in Table T-8.2.

It was noticed that the code formula is slightly conservative for records of intermediate frequency

content, and overestimates t~e recorded base displacement for high frequency excitations. For instance,

DulD..t is about 4 for the San Francisco record. There was a major concern about the underestimated

result for low frequency inputs such as the Mexico City record for which Dw'Dreat is about 0.5. This

is due to the dependence of the factor ZN on the ground acceleration. For the Mexico City signal

those accelerations were very low, nevertheless it was the most severe input for base isolation systems.

One interpretation is that buildings on soft soil need not be isolated, but it is preferable to introduce a

factor that malees the code displacement increase substantially for this case in order to translate the

severity of low frequency ground motions for isolation systems.

The period range recommended by the code does not relate to the particular structure under

consideration, and thus ignores the crucial period band in which amplification in the response might

occur. For this reason. the code formula was also used with an EPA obtained from the average

spednJ a~leration between 0.29 and 1.4 seconds which correspond to the fixed base and to the

sliding conditions. respectively. The r...sponse spectra used was for ~ ciampi.. to matcb the

-147-

equivalent damping of the system calculated from the base shear hysteresis loops. This approach stin

needs some improvement but it gave results that were more consistent with the mcasureJ

displacements. When the average spectral acceleration s;. (0.29 sec < T < 1.4 sec) was used, the ratios

of code displacement to test displacement were 1.32 for EI Centro. 1.05 for Mexico City. 1.10 for

Bucharest, 1.01 for Parkfield, 1.03 for Taft and about 0.95 for the Miyagi. Pacoima and San Francisco

records. Furthermore. the average "PCctral displacement s" was very close to the measured base

displacement These results are listed in Table T·8.3.

3. Base Shear

According to the tentative code, the part of the structure that is above the isolation interface.

should be designed to withstand a minimum shear force of

(8.4)

where the values for the factor Rw, which takes into account the structural system used, according to

the code are the same as for a non-isolated structure but should not be taken more than 8. R,,/2 can be

regarded as a base shear reduction coefficient that accounts for the ductility of the superstructure.

Since one of the important advantages of base isolation is to protect the structure from deforming into

the inelastic range, the expression KefCDcodc was used for comparison with the maximum base shear

obtained from shake table tests. This is equivalent to taking R.,12-1. The stiffness used in the code

base shear calculation is the average equivalent stiffness for the eight records listed in Table T-7.6. It

was noticed that the code overestimates the base shear for high frequency excitations (San Francisco).

and might underestimate it for low frequency signals (Mexico City). The values are shown in Table

T-8.4.

4. Lateral Force Distribution

From the experimental data. the force at a given story level was obtained by summing the inertia

force time histories acting on the part of the structure above this level. Since the damping in the

-148-

structure is very small this should yield the story shear (elastic force fa). This approach was verified

at the base; the base shear obtained by adding up the inertia forces compares well (4 % relative error)

with the forces recorded by the load cells located under the base. From the recorded story shear time

histories of all floors. an envelope for the shear distribution along the elevation of the model was

obtained. SEAONC provides a simplified formula for the lateral force distribution along the elevation

of the building. The distribution is given by

(8.S)

where WI: is the weight at level x, and V. is the base shear obtained from equation (8.4) with the

reduction coefficient R.J2 taken as unity.

5. Comparison with RespoDSe Speetn Analysis

Despite the nonlinearity introduced by the sliders in the properties of the isolation system, the

basic feature of base isolation of causing the building motion to be controlled by merely one mode

shape, was preserved. For instance, by considering Figures 7.7-7.14 which show the deflected shape

of the structure at maximum story displacements, it was noticed that they followed a certain pattern

independent of the excitation. The vectors containing the story displacements relative to the table,

normalized to the highest story displacement (seventh story) varied slightly with the type of excitation

and span. The vector containing the average values for all eight records is

~ • [0.68 0.74 0.77 0.80 0.94 0.96 0.98 1.00 0.92 0.93 JT (8.6)

where the average displacement normalized to the seventh story displacement is 0.68 at the base and

0.93 at the ninth story. Thus the distribution is close to constant along the height of the building and a

vector of ones can be used. However, the vector in equation (8.6) will be used here in a response

spectrum Inalysis, treating the 9 DOF structure and the isolated base as a 10 DOF linear system.

-149-

the response quantity is then given by

L • 4»" m [I) - 0.21

where [1) is a 10x1 vector of ones and m is the mass matrix. The modal mass is given by

the story displacements and story shears vectors are given by:

(8.7)

(8.8)

(8.9)

(8.10)

where S4 and S" are the displacement and pseudo-acceleration spectral values. These can be obtained

from Figures 5.lb-5.8b for a damping ratio of 20 %. since this level of damping was experimentally

determined for almost all applied table motions (Table T-7.6). In the choice of the spectral quantities,

it was taken into account that the isolation system had two distinct stiffnesses. one infinite and

corresponding to no sliding when the base shear is below the sliding tt-reshold, and one that equals the

stiffness of the four rubber bearings. For this reason, the average spectral value s;, was used in

equation (8.10). This approach might be conservative since it uses a non reduced linear response

spectrum, nevertheless it yielded better ~.>rrelation with the test results than the code formula. The

story shear distribution for test, code formula, and response spectrum analysis are shown in Figures

8.1-8.8.

Generally, the analysis using a response spectrum with 20% damping along with the average

spectral values at a period band pertinent to the properties of the structure yielded results closer to the

experimental ones than the code for mula did.

6. Future Research and Conclusions

Earthquake records of low frequency content generany contain low acc::clerlllions, and thus would

result in low values of Peak Table Acceleration (PTA) and/or Effective Peak Acceleration (EPA).

·150·

When these values are used in the code formulas they yield underestimated base displacemenlS which

contradict theoretical and experimental results that low frequency inputs are extremely severe to base

isolation systems and produce excessive base drift. ATC 3-06 recommended using the controlling

value of either A. or ~ in order to account for the high velocities caused by low frequency large

amplitude displacements, however, Ay was introduced as a spectral velocity ordinate corresponding to

one period value. This approach seemed insufficient in descrihing the "Design Ground Shaking"

corresponding to the low flequency inputs used in the present experiment. Instead. a range of periods

of the same width as the one used for EPA but centered around a 1 second period (0.5 seconds for the

model) was used in the pseudo-velocity response spectra. The factor 30 by which the EPV was

reduced to yield Av as was concluded from ATC 3-06 Section Cl.4.1 F, p. 301, caused low values of

Av. It is suggested that for correlation with dynamic test results. the reducing factor 30 should be

replaced by 30IVS wbere S is the geometric scale of the structural model used.

Approximate preliminary design of base isolated structures can be performed by using simplified

formulas. Despite the non-linearity in the properties of the sliding bearing and rubber bearing

combined system it was shown that simplified formulas can predict displacements and forces within

40 % of overestimation. This amount of uncenainty is unavoidable in most preliminary designs.

However, the parameters used to characterize the "Design Ground Shaking" need to be studied in more

detail. In the case of base isolated structures it is necessary that the Velocity Related Acceleration

Coefficient be given a more careful treatment Also, for structural systems tbat might be influenced by

repeated loading, a special coefficient representing the duration of ground motion should be defined.

In general, however, i'lolation systems are tested against cyclic loading before gaining acceptance. In a

response spectra analysis, where the structure was expected to possess varying fundamental period, the

average value of the spectral ordinates between these two periods was used and yielded good results.

-151-

0.192

0.570

0.128

file

ELC375

BUC300

MEX375

Table T·8.l EPA and EPV values with the correspondinl code displacementsfor the eight records used.

A., A.; I A., A., I A.• 'D-:. 0"·1 ~~ -~~

O~618 0.502 j_ ~~9__~.349 0.367 2.S7 2.572~7~ __ ~:~8

0.103 0.088 0.097 0.763 0.564 1.04 1.04 6.18 4.57- f -- - - - -- - ----- --- - -

0.212 0.243 0.239 0.290 0.286 1.46 1.43 1.74 1.72

MIY350 0.255 i 0.319-- t--

PA050 0.468 I 0.337

0.453

0.288

~.;69 I 0.247 0.233

0.289 0.229 0.225

2.72

2.12

2.21

2.11

1.91

U2

1.91

U2

PAR350

SFR200

Tl\F350

0.308

1.096

0.569

0_309 j 0.146

0.592 0~249

0.464 j 0.223

0.151

0.231

0.252

0.216

0.091

0.258

0.219 1.39 1.39 1.39 r 1.39---- - --- --- ~- --4

0.096 3.29 3.29 --~'-'~-r' 1.78_

0.280 2.56 2.56 2.09 2.09- - _._- ._- - ----

A. I between Tt-o·05s. and T1-o·25s.

A.1 between T1-o.lOs. and T:l-o.50s.

AVI at T1-o·50s. ( /30)

Av2 between T.-o.4Os. and T1-o·60s·

AvJ at Tt-I.Os. ( /30)

AV4 between T1-o·80s. and T2-1.20s.

Table T·8.Z Comparison of code displacement with test displacementshowing overestimation for high frequency inputs andunderestimation for low frequency inputs.

-]52-

Table T·R.J Measured base displacement, average spectraldisplacement, and average spectral uceleratiOD over 0.29 sec < T < ].4 sec.

D LHl s:;(in) (in)

ELC375

MEX375

BUC300

MIY350

PAC350

PAR350

SFR200

PAR350

1.36 2.27 162.0

1.91 2.19 96.5

1.27 1.55 91.1

1.22 1.36 100.3

1.30 1.55 106.1

1.09 1.42 92.5

0.84 0.87 81.9

1.36 1.53 110.2

Table T·8.4 Maximum base shear rrom Code Formula, Test,and Response Spectra Analysis.

- Maximum Due .hear

filename F'04t (I:. ) Ftu,(I:· ) F,:.,(I:. ) Fr.,., (I:. )

861119.03 ELC375 36.5 20.2 20.7 38.3

861119.04 MEX375 14.8 24.3 24.5 22.8

861119.05 BUC300 20.7 16.3 16.6 21.6

861119.06 MIY350 38.6 16.5 16.7 23.7

861119.07 PAC350 30.1 17.2 17.4 25.1

861119.08 PAR350 19.7 15.6 16.0 21.9

861119.09 SFR200 46.7 16.0 15.9 16.0

861119.10 TAF350 36.4 18.2 18.5 26.1

-153-

ISTORY SHEAR ENVELOPE II)

~ tI Ii.I ~ IIE- o ~u

::10.6 0.4 0.5

tf'5t.

5.6 4.0 4.5

code eq.

7

:19.5 7.6 8.9

I resp.

6\L_ 12.2 11.2 13.2

F ',11

51 II ..0 13,7 14.8 17.40 I'

r i I41 -r 15.3 20.0 23.4

L

J\

I

e I 16.5 23.6 26.9L

V

e I1

21 17.0 V.2 30.3

1I 17.4 30.9 33.6

II 20.2 35.5 38.3I_J __.1._L J I

_ -.1 .~ ..1 _~~Ll"":'-L_-.-L-L_.~L _

0 5 10 15 20 2S 30 35 40 45 50 55 60

Klpe

Figure 8.1 Story shear envelope from lest, code formula, and response sPKtraanalysis. Table input: J4 time scaled EI Ceatro, horizontal span 375,PfA-O.73g.

-154-

STORY SHEAR ENVELOPE lIII.. • ci.

B 1 Bl- t) Cl::q -1 o 4 0.7. 0.3

tf"!St.

I8~'l

J.6 lob 2.7

:h code eq.7

I6.5 3.1 5.3

r~.

6 l._. __._...~ 9.0 4.5 7.9f

111 I .0 ~I

. ' 11.2 b.O 10.4l0 I 1r

41 13.8 8.1 14.0L 1

,\I

e 15.7 9.6 16.1V 3

e1 2 17.5 11.0 18.1

'l - L20.1 12.5 20.1

_-L_---'-:-:

24.3 14.8 22.8

I _LL -1-__1_

0 5 10 • c 20 25 :Kl 15 40 45 50 55 60. ,KI~

Fipn 8.1 Story shear enl'elope from test, code formula, and response spectraanllysis. Table input: '1/4 time scaled Mexico City, horizontal SpaD 375,PTA-O.llg.

-155-

STORY SHEAR ENVELOPE ltil

~ • ci.! 1 IIl- t) ~

:I0.3 o 2 0.3

t_t.

12.7 2.3 2.5

Icode "'t.

71

14.8 4.3 5.0

L. ...esp.

F£>

~- ~-_.- - - -- _.- ~ 6.7 6.4 7.4

10 <;1 Ii e.:! 8.4 Q.80 I

I

r i4 'j: 10.3 11.3 13.2

Le I

l:v 31 11.7 13.4 15.2

e1 2 13.1 15.4 17.1

r[1 14.3 17.5 18.9

16.3 20.7 21.6

._.L___1--1-L_1I. -.1 ___ .J _..-l__L_. 1..--1.. __

0 5 10 15 20 25 30 J5 40 45 50 55 60Kiptl

Figure 8.3 Story shear envelope from test, code formula, and respoase .peet...analysis. Table input: ";4 time scaled Bucharest, horizontal span 300,PfAaO.27 g.

-156·

STORY SHEAR ENVELOPE lrIl.. • Q.• 1 IIf-o t.l c::

:,I -l 1"1.5 0.4 0.3

tffit

4.1 4.2 2.8

Lt

code eq.7 7.1 8.0 5.5

re;p.6 9.3 11.9 8.2F

1 II:0 5 10.7 J,) .7 10.8- I0 I

Ir I

41 1 11.9 21.2 14.51L

Ie12.5 25.0 16.7V J

Ie I1 2 1_ 12.8 28.8 18.8I

I

1 I __I 13.8 32.7 20.8

I I

I

l_...L--L1 __ 16.5 38.6 23.7I

___I~ 1'- __1

0 5 10 15 20 2S 31 35 40 4S 50 55 60

Ktpe

Figure 8.4 Story shear envelope Jrom test. code rormula, and rupon&e spectraanalysis. Table Input: ./4 time scaled Miyagi-Ken-Old, horizontal spa. 350,PTA-O.33 Ie

-157-

STORY SHEAR ENVELOPE

7

or

4

L ie Iv 3

e1 2

-. I

I

1-

code 6:1.

r~.

i...0.6

4.9

1.9

10.3

12.3

14.3

15.2

15.4

.,"8U

0.3

3.3

6.3

9.2

12.1.

16.5

19.5

22.4

l~A-I

0::0.3

2.9

5.8

8.7

11.4

15.3

17.6

19.9

1 15.1 25.5 22.0

25.130.117.2

605550

,_ L.--i __ J _1 _ ~_---'-__L----'

25 JO 3S 40 45

KIp.

__ L L __:1~o 5 10 15 20

Filure 8.5 Story shear envelope 'rom test, code fonnuJ., and rapoue spectraanalysis. Table input: ';4 time scaled Pacoima Dam, horizontal span 350,PTA-O.49I.

-]58-

STORY SHEAR ENVELOPE 1ft!.. II D.

l! '8 l!

"'"u a:

1]0.5 0.2 0.3

t.~t

4.1 2.2 2.6

I I code eq.

7 ~ 'l 7.1 4.1 5.1

resp.

• '" '1l - .- ----- 9.4 6.0 7.6

f1

I:I:

0 c;': .] 11 .1 8 0 10.0

0 I,r

4' ..,I. [

13.0 10.8 13.4

L I , '

p I • 13,9 12.7 15.4V 3

e1 2 13.9 14.7 17.3

1 I ,: 13.6 16.7 19.2

III 15.6 19.7 21.9

~ -I'-.-.-l__ L .. _JL;_..L--L __ L __...L __ l_L__ L._

0 5 10 15 20 25 JO ~ 40 45 50 S5 60

KIp"

Filure 8.6 Story shear envelope ~m testt code formula, and response spectraanalysis. Table input: -./4 time scaled Parkfteld, horizontal span 350t

PTA-CUI a.

-159-


:~ t.f!!St

IIII ~

code eq.

l__

7 1 I

II rft':P ..6 ' I

F1 Ia 50

r

4\ 1

L I ie

~v 3

e I1 2 , -- I

1 !

1• WI.. 1 Ii.

~ IIC)~

0.6 0.5 0.2

5.1 5.1 2.3

8.4 9.7 4.5

10.5 14.3 6.7

11.9 18.9 8.8

13.2 25.6 11.8

13.9 3(L2 13.6

15.5 34.8 15.3

16.2 39.5 17.0

___ L l. _ I __L _-..1_-1- L_ -L __

o 5 10 15 20 25 30 35 40

Klpll

I

LLL-_

45 50 55 60

16.0 46.7 19.4

Figure 8.7 Story shear envelope~rom test, \;ode formula, aDd respooR speananalysis. Table input: ";4 time scaled San Fraoclsco, hOrDootai spao 200,YfA-l.20 g.

·160·


9 ..

~t'St

8 i~

"[ \[II

code eq.7

relp.(, --'--F

I 11 . I0 51 '. II0 Ir

4\ lL IeV 3

e I

1 I2 .- 1

1 -- ,

IfIl.. • Q.

IS 1 I... u a:0.7 0.4 0.3

5.9 4.0 3.1

9.9 7.6 6.1

12.1 11.2 9.0

14.2 14.8 \1.9

14.9 20.0 15.9

15.3 23.5 18.3

15.3 27.1 20.6

15.2 JO.B 22.9

26.136.418.2

55 60so4540

IL_--..L.-...1. _.-I .LI_L--.l.._-L_.-L--.J

20 25 JO 3S

Ki.,.

~1L_L_j~_

5 10 15o

Figure 8.8 Story shear envelope from test, code formula, and response spectraanalysis. Table input: ';4 time scaled Taft, horizontal span 350, FrA-O.72 I.

-161-

CHAPTER NINE

CONCLUSIONS

Various base isolation systems have previously been proposed but most of them need separate

accessories to provide wind restraint, displacement control, stability and fail-safe capacity. Systems

that provide large reduction of ground accelerations usualJy consist of horizontaJly flexible rubber

bearings solely. These, however, might present stability problems in case of accidental excessive base:

drift, and thus need a support on which the structure can depend in case: of bearing buckling or roll

out. Furthermore, the damping that elastomers provide does not always meet the level of energy

dissipation needed. On the other hand, a system that is very economical and close to existing practice

consists of frictional elements currently used for purposes other than earthquake protection. In this

study, these two systems were combined into a new one that satisfies all requirements for the

earthquake isolation of structures. The threshold of sliding provides wind restraint, the friction

provides energy dissipation. the reinforced rubber bearings carry part of the vertical load and recenter

the structure, and the tension restraint keeps the structure from uplifting. Furthermore. since the base is

constantly resting on the sliders. (he fail-safe capacity is inherent.

The earthquake simula(or testing showed that the inclusion of teflon sliders in the base-isolation

system drasticalJy improves (he control of displacements at the cost of slightly reducing the

acceleration reduction efficiency of a solely rubber system. For the same model. where fixed base: tests

resulted in acceleration amplification ratios as high as 6. the combined slider-rubber system yielded

ratios around 1, whereas a solely ruhbc:r system typically yields ratios around 0.5. The solely rubber

systems, however, resulted in base displacements around 3 times the ones that correspond to the

combined slider-rubber system.

The high energy dissipation is characterized by the large area enclosed in the base shear

hysteresis loops. and on the average the system provided an equivalent damping of about 20%.

The so-called Alexisismon system uses sliders combined with unreinforced neoprene pads that act

as restoring springs (16]. This system has two major differences from the one described in this report.

The neoprene springs in that system ue not allowed to carry any axial load and all the weight of the

·162·

building is carried by the sliders. This causes the base response, specifically the base shear sliding

threshold. to be totally conttolled by the weight of the building and by the friction coefficient of the

sliders which changes witb velocity. temperature and pressure. Thus, the above arrangement does not

allow the designer to disttibute the weigbt of the building on botb sliders and reinforced bearings. In

the present system, the base shear threshold can be better controlled by appropriate choice of the size

of the sliding area which can be decreased to a very low percentage, since sliders here are not required

to carry the total weight of the building. On the other hand, excessive drift of the base may cause

tension in tbe neoprene springs and thus make them more vulnerable to external factors such as ozon(.

attacks. while in the case of tbe reinforced rubber bearings used here, they are initially under

compression by carrying a fraction of the weight of the sttuclure and this risk is eliminated. In the

case of accidental excessive base drift, pan of the vertical load that is initially carried by tbe rubber is

transferred to tbe sliders and prevents the rubber bearings from buckling.

Many analytical studies hav~: been performed on such systems and mathematical models using

equivalent linear systems have been proposed but none of them accounted for the varying friction

coefficient. The dependence of this coefficient OD the velocity of sliding is important since it causes

stiffening in the system as the base relative velocity increases. Numerical derivation of the measured

base displacements on the sbake table yielded sliding velocities of up to 12 in./se. A variation of this

magnitude causes the tefton coefficient of friction to change by a factor as high as two. thus doubling

the shear resistance of tbe sliders.

When the results from formulas recommended in 1986 by the SEAONC seismology

subcommittee for the design of base isolated structures were compared with the measured values. the

displacements were found to be overly conservative for earthquakes of high accelerations and

frequencies. and were underestimated for low frequency inputs. The base shear and the force

distribution code formulas need to be examined in more detail since they yielded values as bigh as

three times the measured forces for some earthquake inputs. More specifically. tbe coefficient Rw nee~

• more careful iDterpretatioo siDce it wu initially defined fOI aJnvcntionally dcsigr.ed fixed base

Itrueturea that are expcc:tcd to dissipate energy by yielding. A simplified approacb using a response

-163-

spectra analysis, that was considered. yielded satisfactory results.

-164-

REFERE~CES

(1] Kelly 1. M., "Aseismic Base Isolation: review and bibliography", Soil Dynamics and Earlhquake Engineering, Vol. S, No.3, 1986.

[2] Kelly J. M., and Tsztoo D. F., "The Development of Energy-Absorbing Devices for AseismicBase Isolation Systems", Report No. UCBIEERC-78101, Earthquake Engineering ResearchCenter, University of California, Berkeley, California. 1978.

[3] Kelly J. M., and Chitty D. E., ''Testing of a Wind Restraint for Aseismic Base Isolation",Report No. UCBIEERC-78120, Earthquake Engineering Research Center, University of California, Berkeley, California, 1978.

[4] Kelly J. M., Beucke K. E., and Skinner M., "Experimental Testing of a Friction DampedAseismic Base Isolation System with rail-Safe Characterisitics", Report No. UCBIEERCB0118. Eanhquake Engineering Research Center. University of California. Berkeley, California, 1980.

[5] Delfosse 0. c.. "Full Earthquake Protection through Base Isolation System". 7th WorldConference on Earthquake Engineering, Istanbul, Turkey, Vol. 8, p. 61, 1980.

[6] Plichon C., Gueraud R.• Richli M. H., and Casagrande J. F., "Protection of Nuclear PowerPlants against Scism". Nuclear Technology Vol. 49, pp. 295·306, 1980.

[7] Taries A. G.. "The Implementation of Base Isolation for the Foothill Communities Law andJustice Center", Report to the National Science Foundation and the County of San Bernar·dino, Reid and Taries Associates, San Francisco, CA, 1984.

(8] Walter M.• Elsesser E., and Allen E. W., "Base Isolation of the Existing City and CountyBuilding in Salt Lake City", Proceedings, Seminar on Base Isolation and Passive EnergyDwipation, ATC·17, Applied Technology Council, San Francisco, pp. 113.122, 1986.

[9] Stanton J. F.• and Roeder C. W., "Elastomeric Bearing Design, Construction and material",Report No. 248, TrallSport"tiOtr Research Boord, N"tional Research Council, pp. 17.27,Washington D. c.. 1982.

[10] Chalhoub M. S., and Kelly J. M.• "Reduction of the Stiffness of Rubber Bearings due to

Compres~ibility".Rt!pOTt No. SESM-86I06, University of California, Berkeley, 198t.

-165-

(11] Aslam M., Godden W. G., and Scalise D. T., "Sliding Response of Rigid Bodies to Earthquake Motions". Report to the U.S. Energy Research and Development Administration,Lawrence Berkeley Laboratory, 1975.

(12] Tyler R. G., "Dynamic Tests on PTFE Sliding Layers under Earthquake Conditions", Bulletinof the New Zealand National Society for Earthquake Engineering, Vol.lO, No.3, September1977.

(J3) Taylor M. E., "PTFE in Highway Bridge Bearings", Report No. LR 491, Transport and RoadResearch Laboratory, Department of the Environment, Crowthome, Berkshire, 1972.

(J4] Base Isolation Committee of the Seismological Committee of the Structural Engineers Association of Northern California, "Tentative Seismic Isolation Design Requirements", SEAONC,1986.

[15] Applied Technology C.cunei!, "Tentative Provisions for the Development of Seismic Regulations for Buildings", ATC 3-06, June 1978.

(16) Jkonomou A. S., "Alexisismon Isolation Engineering for Nuclear Power Plants", NuclearEngineering and Design, Vol. 85, 2, pp. 210-216, 1985.

-167·

t:ARTlIQl..-\KE r:";GI:";U:RI:-\G RESE\RClI Ct::-\HR REPORT SERIES

EEK(' rC'~)n~ .1TC a\31lahk from thl' :\allunal Infllffnatlun St"n 1((' fur F.arthqual.;.c Ehl:lnt"rnnlt.tNISEE~ and from the Nallonal TC'lhr'llcal InformallonS('n.ll·e(~TISI ~um~r\ In paH'l\lhc\('\ ale ~i(C"\'lon NUnlbcr~ a,'),gned b\ the.' ~allonal TC'chnll"allnfonnallOn X-n'l(('. th~' arC' followC'd b~ ill prl<"C' code.

('notal! ....;TlS. ~~~~ Port R(l~a1Io(oad, SpnnJfleld \,1ff-IOia. ~~It1\ fur mOTe lnformallon Rtpun\ wllhmal ~ccC'\\lon Numbr'rs wrore nOll\'III,blC' from NTISJl thC' tIm!." uf prlntmg For a ("unto. l\lmpl~tl" list of EER(' ft"pOns (frum fliH' fl~·I) and i\31labhlY Information. plr3~ contact 1l0l\'[,r'ul) of California.H RC ~JSfE. IJil! Soulh 4b.h S'n'c' Rllnmond. Ca"'orn,a U4~114

lcn l! RC-~ I ill COnlrol of Sellm" Rc'pon,c of PIP'"~ S~<I<m, .nd Plh« SIrU,·lu,., b~ BJ,c holallon. - b, Kdl). J.M., Janua" 1981. fPBSI ~oo

'1;1 ...0;

\:CH fFRC-~I,U~ l JPT!':SR- An Int("r~CtlH' ~oh""iJr( S)"\H"m for Ofl\lmal ()eMgn of Stallcall~ and D~'namlCall~ Loadfd Structurt~ "'llh Nonhn~ar

R,·,pon".. I" Ilh.",. M.~ C,aml'i. \' and P"I~r "-.S Janua" IqSI. iPllSI ZI8 8S11Au9

t'l K Eli(( sl,'U~ ""'nal~~lc; of LO{JI \'anallom. In FTC'c flr'ld SC'I~mH.- t'rvund MOllon): ll) Chen, J.-C. l~~mC'r. J. and SC'C'd. H.8,. January 1981. (o\D

~IN~'IISI"'I.1

l'CB EER( .81,(14 In<l"tIC Stru,tural Mod~hn~ of 8rat'~d (ilf,horc Plalforms for Sc"mK loadln"- b) Zara,. V.A .. Shine. P.-S.B., Mahin, S .... andI'opm E 1'. Janua') 1981. l"'El~. IPIlS~ I}~ ''"1...0'

lTIl lERC-S 1/\1' . D' n.m,c Rnplln'r of l,~hl Equlpmcnt In Slruclure,: b, D<r K,urogh'an...... s..ckman. J.I- and Nour-Omld. B., Apnl 19S I, (PBS I; I ~ ~u'I"'()~

lTB EERC-SI·Ob I'rel,mln." bpcnmcnt.llnw,tlgallon of. Broad OJ'" L'4U'd Stvra~e Tank. by BoUWkamp, J.G., Kolleuer. J.P. and Slcpn<n. R M..M.) IUSI. (1'IlSZ 14(1 18;1~('}

"C8 [ERe-t.;! 0" r hL~ Sl"l~ml'o.. RC..,lstant [)(."",g:n c." RL"lnforn'd Concrr:tc Couplc.'d Structural ",'all!l." b)' Aktar.. A.E. and Brn('ro, V,V., June 1981. (PRR~111 ,;St·\11

I'CIl,EERC-8I'()S l'na",~ncd. [" l·na>\I~n«!. IQSt

I :CH'ErR(·XI,'UIJ L\.fwnmt."'lll.al tkha\lnr of a SpallaI Piping SY!'iltl'm wIth Stl'cl rner~~ .-\b~orber~ SUbJtftcd tu a Simulated DI!ftrCnllal StlsmlC Input: b~

St,emn SF .lillddcn. we; and "-~III. lM., Jull lu81 (1'IlS; ~Ol 89S) ...04

t:CH EEKC-~l. 10 E\aluallUn (If St:'I~mH.: Dnl~n Prm,mons for Mawnry In Ihe t~",ll~d State\: b) S\(~I0'\"",on. 8.1,. Mayes, R.L. 4nd Md,,\'en, H.D...... ugUst IUSI. ,PIl~; 166 0751~(l8.

l'CB'EERC-SI/I J -T"o-IJ,m<"mlOnal Hlbnd Mod<llwr of Sod-Slrurlu« Inlfr.,·lIon: 01 Tlone. T.-J. c.upla. Sand PcnlJtn. J. AUBust 19&1. (PB82 14;II~I~O~

L'CBf-ERC-81, I~ 'S'ud,e> on Elfect> vi lnhil, In S<t<m,c R~"'tanl RiC Con<lruellon: by Brvkken. Sand Bcncro. V.V., OCtober 19&1, (PBSZ 166JUOI·\(l~

l'CH'EERC·XI 13 Linear Motkl\ 10 l)r~dICI the l'ionhnear SeismIC Bl·ha\ lor of a ()ne.Sto~ SleC'1 Frame: by Valdlmarsson, H., Sha~l. A.H andMd",,·rn. H D. Srptrmber luSI.IP8S; I1s ,91,"'0'

I'CB EERC-SI 'I~ -TlI'SH -\ Compulor Program (or Ih< Thr<f-D,men<lonal Dlnaml( ....n.I~'" of Earth D.m,'- h~' Kagawa, 1. M<j,a. LH., x<d. H Bar.d lnmer. J .. S<p,cmher 19KI. (P8S~ 139 94U\-\Ob

I ,(,B'EERC·SI' I j Thrcr I)mlcn>lon.1 D)naml< Ro,pon...-\nal)", of Eanh Dam,'- h, MCJ,a. LH and Se<d. H.B.. S<ptember 19&1, (PBSZ 137 2741AI~.

ITREfRC·SI·16 bp<'nm<nlal Stud, o( uad and ElallOmen< I).mpe" for Has< Iloiallon Sy"ems.- b~ Kelly. J.M. and Hodder, S.B.. Ocloher 1981,,PRlIZ 16b 18~,-\05

I "R'[ERe·SI,I' Thr Influence of 8.« 1;ol.lIon on the S<-"mlo R.,ponsc of LIght Second.') Equlpment'- b) K<II). J.M. "pnl 1981. (PBSl lS;ZM" ...1i4

I TB'EERC-SI II ~ Slud,e, on haluallon of Shaking Table i<e,pon", Anal'''' Procedur<': bl Blondel. J. M . Nov<mber I 9&1. (PB&~ 197 ~781" 10.

t:CR'EER'·8LIQ ·DELI(iHT.STRI'Cl -\ Compul<r-Alded De\lgn En'lfonm<nt for Slrue,ural [nglnr<rtng.- by Ball,ne. R.J., PISter, K.S. and Polak. E.,D.ccmhC'r 1981. (PR8~ liS 4Q61-\07.

t'CBEERC-~ II~O 'Optlma' D<:,,~n of Smm,c-Re,,'I.n' Planar SI«! Framc,: b, Dalhng. R.J .. C,amp,. I' .nd P,st... 11:.5.. December 1981. (PB8~ Z~O

1'9).-\07.

L:CBIEERC·8~/OI -I)'naml< 8<h."or of Ground for SeISmIC ....naly'" of llf<hne S~'I~ms: b) Sato. T. and Der "-iur.-ghlan. A.. January 1982, (PR&~ 21&9~61-\OS

I'CR:EERC-gZ/O~ -Shakmg Table T.-" of. Tubul.r S..el Fr.me Mudd: b) Ghanaat. Y and Clough. R.W .. January i98~. (PB8~ ~~O 16\).1<07

1'C1tEERC-8l!03 -Ren., lor of a PIPing Sy<l<m und<r S<"m,c ExntallOn: bpenmenlallnve"igations of a Sp,1llial P,p,nl Syslem supponrd by Mrchan,cal Shock ""'«110"'- b) SChneIder. S., lee. H.-M. and GOOd<n. W. G .. Mal 198~, (PBS3 J7~ 544)A09.

I TBTERC-8~'(J4 'Se" -\I'proachc, for th~ Dynam,c ....naly'" of larg< Slructural S~S1em,'- by Wil;on. EL. Jun< IQ8~. (PB83 148080,,\05.

I TII·EERC·8Z/o5 . 'lode! Stud~ of Eff.cts of Damage on Ihe V,bralion Propen,e; of SI«I Olhhore Plalform,.- by Shah",'ar, F. and Bouwkamp. JG.Junc IQ8~ (1'8K' 14S '4~'-\10.

UCB!EE~C-8~'{)6 'Slal« of th< -\n and Pra"e< In Ih< Opllmum S<"mIC De,,~n and Analrllcal R<lponse Pred/cllon of RIC Framt W.II ~Irue'urt.: b)~klan. ~ E and Ben<ro. \'.V .. July lQ8Z, IP.IS3 147 716 lAO;.

UCB'EERC·8ZI07 'Funher Slud\ of Ihe hnhqu.k< Response of a Broad C,hndneal LJquid-Stora~<Tank Mod<l: by Mano;. Or. ond Clough: R.W.Jull 198~. IPBS3 !47 744';\1 I.

L:C8'EERC·S~IOS ....n [valuallon of Ihe [)<sIgn and Anal)l"al Se"m,c Respons< ofaxven Story Reinforctd Conerele Frame: by Cham<)·. F.A. andIknero. V.V.. July 1982. (P1S8) I S7 1'>~&IAoq.

I'C8/[ERC·H~/09 -Flu,d-Struclur< lnl<raelion;: .;\dded Ma.. Comrulatlons for Incampr<s..b/< flUId: by Kuo. J.S.-H .. AUlus, I9S~. (PBS3 156 ~SI }.A07.

VrB'EERC-&~ 10 "Jolnl-Openong Nonltnear M«hanJsm: Inl<rfacr Smeared Crack Mod<': b) Kuo. 1.S.·H.. AUluS! 19S~. «PBS3 149 19SIAOS.

-168-

L'CBIEERC·R' II . I),n.m,c R"po",e\n.h", of Tech, Dam. ~,Clough. R W . Stephen R ~1 .nd Kuo. JS·H . "u~u" I~~~. (l'B~1 14' 44~)"[J6

LJCBiEERC·8~/J~ Prediction of lht SeismiC' Rr~p()nl,e of R'C FramC'-Coupll"d Wall Strunurn b} A~lan. -'E. Dc-nero, \' V and PlilUO. M '\'ugU\t

IQ8~. '1'1183 14Q ~Oh"U9

l'CB·'EERC·8~!13 'Prehm.nary R.pon on the Sm.n I Strong MOlOon Arra) 10 T., .. an.' b) Boll. II .... loe C.H .. P.nll.n. J .nd 1",.. Y B. "ugu"191i~. (PB83 15Q 400IA 10

lJ(,BIEERC·8~i 14 SelSm.e Beh., lor of an Ecrcntnc.lly X-Braccd Steel StruClure'- h Y.ng. MS. Serl<' '~'r 19b~. IPB83 ~60 7'81.. 1:

l'C'B:EER(,·8~/15 'The p.rfonn.ncc ofS...",.y, In Eanhqu"e,'- by Roh•. C .... l<y. J Wand Ben,ro. \' \' St"pteml><r 148~.lpBb3 1~7 603,-\U'

LJCB!EERC-3~I'~ ',l;, Beh,Vlor ofSubmHg.d Muillplt ~od,.. '" Eanhqu.k...- by L,.o. Yo' ·G. St"ptember ;98~.lpR83 1~8 70~I"O~

lICBiEER('-d~!l7 'Effect, of ('oncrete Type, .nd loading ('~ndJlJon.on Loc.1 Bond·SlIp RcI"")n,hlp,. ~,('o...ell ... D. Pop",. EP Md Iltnero. \' V..September IQ8~. (PB81 IS3 S"1"'04

ll(,B;EERC-8~'18 'Mechanlc.1 Beh."or of Shear ......11 Ven,c.1 Bounda" Members. An hpcnmental Inve,"g.lIon.- b' Wagner. M T and Benero. \'.\' ..October IQ8~.IPB8J IS9 '(>4'''05

lJCBIEERC-8~'19 'bperomental Stud... of Mulll.,uppon Se"mlc Loadang on P,pong S"tem,.- h, Kelly. J M and (0....11. AD. No.ember 191i~. I PINn~6~ 6841..07.

lICB/EERC-8~/:O 'GenerahlCd PI.",c H,"ge ('oncept, for 3D Be.m-Column Element'." by Chen. P. F.-S and Powell. G.H .. l'o'.m~r 198~.IP8~' ~47

9811 .. 13.

VCB!EERC·8~!:1 · ... r-:SR·II General Computer Program for Nonhnrar Stru,·tur.! "nah",'- b~ Oughourhan. C\' and Powell. GH. No'emher I~~~.

IpB83 :SI nOIAI:.

U(,8/EERC·8:!:/~:! 'Solutlon StraleglC'! for Statlcalh Loadtd Nonhncar Strul"tureos: b~ Slmon~, 1.\\' and Po...·dL GH, Nov("rnht-r 1~1'l:!. (PB8J 1979701"'06.

lICBIEERC-8~!:3 -"'nalytlcal Model of [)efonnrd liar Anchorag.. under (jrnerailled bCltallo..'- by CiampI. \' , ElIgeh.u ...n. R. Benero. \,Y andPopa'. EP.. No.ember 1~8:. (PB83 16~ 51:,"06.

LJCBIF.ERC·8~'~4 ... Mathemahcol Mod.1 for the Re.pon.. of Mawn" Wall, to Dyn.m,c htllatlon,'- by Sucuoglu. H.. Meng.. Y.•nd MeN"en. It.l>.NO"embe, 1982. {PBSl 169 01l)A07

UCB/EER('·8:;:5 'Eanhquake Rtspo",. Con"derallo", of Broad LIquid Storage Tank• .' by Cambro. F 1.. Noycmber IQ8~. (1'883 ~51 ~I S'''09.

UCB/EERC·82/:6 Tomputallon.1 Mode" for C'chc Pla.IIC1ty. R.te [)ependencc and Creep.- b)' Mosaddad. B and Powell. GH. '1o...m~r 198~.lP8g.1

:4S 8291A08.

LJCBiEERC·83IOS

UCB/EERC·82/27

lJCBIEER('·83/03

lJCB/EERC-83/04

-Inelastic An.ly", of P,pmg and Tuoula, StroClu,..,: b)' Mahasu'·eracha•. M. Ind powen. G.H .. No'.mbe, IQ8~. (pB8l 149 987'-\07.

'The EconomIc Fca"b,I,t~ of SeIsmIc Rehablhtallon of BUildIng. by 8..e lsolallon'- b) Kell)'. J.M .. Janu.ry 1983. (PB83 197 9881."OS

"Se,smlC Moment Connecllon, for Momen,.Rem',"g ~tetl Frame• .' by Popo,. EP.. January 1983. (pB83 19S 4!~I"04

'De"gn of L,"k, and Beam·to-('olumn ('onnect,on, for EcceOlne.lly Bracod Slfcl Frames: by Popo'. E p. and M.lle). J.O.. Janua"1983. IPBS 3 194 81 I )..04.

'Numencal Technique, for the Evaluat,on of So,l,Strllcture Interachon Effee" an the TIm. Doma,": by Bayo. E. and W,I,on. EL.February 1953, (PB83 24S 605 ....09

·A Transducer for Mcasunng the Internal forces In the Columns of a Framt·'Wall Reinforced C'oncr:'lt' StruC'lurr: h)' SauM:. R. andIknero. V. V .• M.~· 1983. IPB84 119494'4.06.

'Dynamlc Interacllons B<lw~n floating Ice and Offshore Structur«: by Croteau. P.. M.y 1983. (pB84 119 486)AI6.

-Dynamic Analy... of Muillply Tuned and Arbnr.nly Suppooed Secondary Systems.' hy' Igusa. T. and [)er Kiureglllan. A.. Jul~' 1983.(PB84 118 2721AII

".. Laboratory Study of Subme'led Muill'bo<!y Sy'tem. '" E.ohquakes.· by Ansan. G.R.. June 1983. (PB83 261 84~'A I i.

·Effect. of Trans.ent Foundallon Uphft on fanhquake Respon« of Structures: by Y.m. C·S. and Chopra. A.K. June 1983. (1'883 261396)A07.

'Opllmal De",n of Fncllon,Bracod Fram.. under Se"m,c Lo.dln,: by AU\lln. M.A. and P",er, K S.. June 1983. (PB84 119 288\..06.

-ShaklO' Table Study of Smpe·Story Mawn') Hou«s: Dyn.mlc Perfonnance under Three ('omponent S<1.mlc Input and R<commendalIOn.: by Manos. Gc., C1oup, R.W. and Mayts. R,L.• July 1983. (UCBIEERC·83/1IlA08

-Expt'nmen,.1 Error PropapllOn in P«udodynam,c Test,nl-' by Shiinl- P.B. and Mahin. SA. June 1983. IP884 119 2701A09.

'E'pl-rimrnlll Ind AnllYllel1 pred,ctions of the Mechanical Charactensll<S of I liS-scale Model of a 7-story RIC Fr.me-W.1l Bu,ldln'SUUCIUrc'- by Al,an. A.E.. Iltnero. V.V .• Chowdhury..~.A.•nd N......hlm•. T.• June 1983,11'884119 2D'A07.

'Shak,na Tablc Tests of Larae-Panel Pr«ast Concrete BUlldlOl System A,sembl.&<s: by' Ol,,·a. M.G and Cloup. R.W.. June 1983.(PB86 ) 10 21O/AS)AII

UC8/EERC·83/1~ ·Sc.smlc Ikha"ior of Actlv, Bea... Lonks.n E«enlncall)' Br""N Framf\: by HJelm"ad. KD and Popov. E.P.. July 1983. (PB84 1196761.0.09.

lICB/EERC·83/08

lICBiEERC.83109

VCB/EE RC·8 311 0

UCB/EERC·83111

UCB/EERC·83114

UCB/EERC.83/06

UCB/EERC-83/07

UCB/EERC·n/o I

VCB/EERC·83/12

UCB/EERC·83113

UCBIEERC-8310~

UCB/EERC·13/16 'System Idenllflcallon ofStru"tures with JOlnl Rotallon: by Dimsdal•. J,S.. July 1983. (1'884 192 2101A06.

VCB/EERC-I3!17 'Construction of InclaSlic Res,,,,... c~.:.:::-: '~r Sinclc-Dqrte-of-Frtedom Systems: by Mahin, S.•nd Lift. J .• JUftt 1983. (PB84 208834).-\05.

VCBlEERC·13/18 "Interacllve Computer AnalySIS Methods for Prcd,cllncthe InelastiC Cycbc Behaviour of StNctural Seellont: by Kaba. S. Ind Mahin,S.. JUly 1983. (I'B84 192 012)...06.

UCB/EERC-I3/19 "ElI'oos of Bond DtlmorallOfl on Hysteretic Beh.Vlor of ReInforced Coneme J'>lnlS: by Fihppau. F.e.. Popov, E.P. and Benero. VV,.AIIIU" 1983.IPB84 192 020)AIO.

ll(,B:HRC·~ J ':0

UCII·EER(,·H~I

I T,B'HRCSJ'::

I '('B·EERC·8JJ:3

I'CIl EIRC·831:4

I'CB EER('·84·01

I T('B'EERC·84!lIJ

ICII/EERC·84 I04

ICB'EERC-k4/0~

I:CB·EERC·8410~

I'CB/EER(,·84/07

\ ICBiEERC·84108

LI('B,EERC·84/09

UCB/EERC·84 ' 10

tJC'B/EERC·84111

UC'8/EERC·84/1:

LJC'BiEERC·841 I3

I 'C'8IEERC·84/1 4

UCBIEERC·841 I 5

UC'BIEE 11.('·841(6

UC8IEERC'-84117

UCBIEERC·84118

LJCB/EERC-841/9

I..TBIEERC-84!:0

UCBIEERC·8'/lJl

UCBIEERC·8S/02

LTB.EERC·8S/03

tJCB/EER('·85104

UCB/EERC,85/05

L:CB/EERC·85/Q6

UCB/EERC·8SI07

U{'B/EERC·8SI08

UCB/EERC·8SI09

·169-

('",r<l.llon "f .... nalyllea! and hprnmenlal 11."1"'"'" uf urse.Panei l'"ca.1 BUlldln~ Sy"em,.· hI 01"•. MG. ("Iough. II. W.. Vel·k"'. M and (i.wlo,x. P.. M.y 1~88. iPlI~O :6: 64:I...U6

-Mrchanlcal Chara('ttn'Jitlc~ of Matenal~ l;5t'd In a I·') S;alr Mod~l of a 7.S,o~ RC'anforu:d Conrrrir Trost Structurr: h~ Brrttro. V.\' ...U,.n. 4 E. Harm. II G .nd Cho...dhur). A ..... OClohc:r 198J.IPB84 193 6~7}""05

H,bno ModrUml of So.I·Slruelu," InJrraw"n m u)rrrd Mrd'a.- bl Tlong. T-J lind P<nllen. L Oetobtr 1983. (PB84 19: 17810\08.

Loc.1 Bond S"r,,·SlIp RrI'llon,h,p' of Orformrd Ba" under C;rnrrahzrd ElellallOns: b) EhgrblUsrn. 11. .• Popo" EP. and Iknrro.\. \'. Oclohc:r 1~8 3.IPB84 19: 8481A09

'0,,"8n ("on"defat",n, for Sh.ar Link. In hernlnc.lI) Braerd Framrs: b) M.Ury. J.O and POPO'·. EP. No"rmbt!r 1913. lPB84 19:I St>l-\07

'P",udodynamlC Te" Melhod fc- S."mlC I'ertorm.ncr baluatlon Thro~ and Implrmrmallon.· by ShIRg. P.·S8. aDd Mahin. S.".,Janua" Ivb4. (!'Bb4 I YO b44'A08

'[)ynamlC Re>ron", Behanor of K.anl Hong D••n Dam. ~,C1ough. R W., Ch.n&. K.-T .• {'hen, H.·Q. and Strphen. RM .. Apn! 1984.IPBg4 :(!4 4"~'A[)8

'Refined Mod<llIng of Reinforced ('oncrete Column, for S."mlC Analy",,- ~) Kaba. S.A. and Mahin. SA, April 1984. (PB84 13418414(16.

.... Ne.. Floor Rrspon.. 5prctrum Method for S."mlC An.ly." of Mulllpl)' Supponrd Second.ry Systrm,: b) A'fura. A and DrrKlurrghlln. A. Jun< 1984. cPB84 ~39 417/....06

"Earthquake' Slm~liltll.:Jn Tr5ISo and ASSOCiated S\Udlt''i of a I fSlh·s.c31~ Mod~1 of a 1·Sto"",' R.X" Fram~.\'tall Tr-'St Struc1ure.' h)" Be-rtero.V\' .. Aktan. A.E.. Ch.m<j. F.o\. and Sau5<. R. Jun< 1984. (PB84 ~39 4091"09.

'Una",gned: b\' Una",gncd. 1984.

'8ehanor of Intmor .nd Extrnor Flat·PI.te C'onnecliom .ubJrctrd to Incla.lle Load Reversal•. - b) z.r. H.L. .nd Machlr. J.P., .....ugust1984. lPB86 117 629/AS''''07.

'hpcnmrntal Study of Ih. S.ISmlC Ikhl\lOr of a T"'0-510r) Flal·Plale 5lructurr: by Moehle, J.P. and Drrbold. JW., AU8u.I 1'l84,IPB86 112 5531"SI"11.

'Phenom<nologlCal Modehng of Slrcl Brac.. undrr Cyche loading: by Ikrd., K.. Mahin. S ..... and Drrmiluki•. SN .. Ma) 1984, (PB86131 1981ASIA08

'Earthquak< ADaly", and Rr>ponsc of Concrrle GnVII) D.ms,- by Frnv«. G and Chopra, A.K.. Augu.t 1984. (PB8S 1939011,451-'11.

'EAGD-84: .... Compu"r Program for ~anhquakr Analy", of Concrrtr GU\,lly Dams,' b) Fen".., G. and Chopra. A.K.. "U8u.t 1'l84.lPB81 19J 613:;5'AOI

..... Rcfinrd Ph}"c.' 1hrory Modrl for Prrd,cllnl the Se"mlC Ikh"'lor of Braced Sirel Fnmes: by Ikrda. K. and Mah,n, S.A.. July1984.IPB8S 191 410/ASI.o\09

-Eanhqu.ke Enpncrnnl Research allkrkrley - 1984: b) EERe. AUlust 1984. (PB8S 197 341IAS)AI0.

'Modu!t and Dampm. Factors for Dyn.m,c ....naly... of Cobe..onl... Soil•.' by' Seed, H.B.• WODl. RoT.. Idnss. 1.1.1. and ToitimalSll, K.,s"plrmbcr 1984, (PB85 191 46bIASI....04.

'The Innu.nc< of SPT Proc.du,.. In 5011 L!QuefactlOn R....t.ner Evaluallon•.• b) Seed. H.B.. TolumalSu, K., Hard... L.F. and Chun&,R.M .. Octobt!r 1984. (PB8S 191 732IAS)A04.

'S,mphhrd Procrdures for Ihe haluahon of Sellirmenls In Sands Dur \0 Eanhqual<r Shakin&,- by Tol<im.tsu. K. and Seed, H.B ..Oclohc:r 1984. (PBS5 197 887/AS)403.

'haluallon of EnrfllY A""'rpllon Cbaracrrmlles of HIgh",.) Bnd,r. Un"'. SeISmic ConchlIons • Volumr I (PB90 26: 627)A16 andVolume II (Apprnd,c«) ~DB90 ~6: 6311"'13.' by Imbsrn. R ... and PenZlr•. 1.. Seplembt!. 1986.

·~\ructur<·Found'lIon InlmclIons under DynamIc Load.,' by Liu. W.O. and Penzien. J., Novembt!. 1984, (PB87 1:4 889/AS)AII.

'SelSmlc Modelling of Deep Foundalion.: b) Chrn, C·H.•nd P.nz..n, J.. Novrmbt!r 1984, (PB87 124 798/AS,A07.

'Dy'namlC R..pon", Bc:havior of Qu.n ~l.u, Dam.' b) Clough. R.W.. Chang. K.·T.. Chen. H.-Q., Slrphen. R 1.1., Ghanul. Y. and Qi,J.,H .. Novemhc:. 1984. IPIl16 1151'77/AS)A07.

'Simplified ".',hoch .. ' Anal),,, for Eanhquake R"l5l1n, Drsian of BUildlnp,' try Cnaz. E.F. and Chopn, A.K., Frbruary 1985, (PB8611::99/AS)"I~.

·EsI,m.tion of Sel5mlC Wavr Co~..rnc) and Rupture Velocity u.ing Ihe SM....RT I S'rons-Mollon Array RCC:ordinp,' bj Abrabamwn,N..... ., March 1985. lPB86 ~/4 3431"07.

'Oy'namlc Proprn"s of a Tb,n) SIOr) CondomInium Tower Buildln&,' b) Stephrn, R.M.. Wilson, E.L. and Stander, N.. April 1985,(P086 I 1896S1"S,"06.

-Dr"r'opment of Subslruclunng Tcc:hnlqucs for On·Line Computer ContrOlled s"ismic Pmormance Testinl: by Dermllukts, S. andMabin. 5., Febru.ry 1985. (PB86 132941/AS'A08.

'A S,mplr Model for R"nforc,n8 Bar "nehora... under Cyclic Excitations: by Filtppou. F.C.. March 1985. (PBg6 112 919/A5)A05.

'Racklng 8eha\"or of Wood-framrd Gypsum P.nrls undrr DynamIc Load.' by DIt"a, M.G.. June: 1985. (PB90 262 64)A04.

·E.anhquake AnalysIS and Response of (on=1r Arch Dams: by Fok. K.-L. and Chopra, A.K.. June 1985, (PB86 I39672JASIAI0.

-EJre.~ of Inr'aSl'c 8eh.v,or on tbe AnalysIS and Des'ln of EanbqlUk" RnlS,ant Strvcturcs.· br Lin, J.P. and Mabin, S..4 .. June 1985,(PB86 135340/ASI....08.

-Eanbquak. SImulator Tesnnl of a Basr·lsolaled Bridgr Deck: by Krlly. J.M.. Buckle, I.G. and Tsai. H ..e.. January 1986. (PBI7 1241521ASIA06.

·170·

UCB'ElRC·1I5 10 'Slmphtltd !\nal~~I\ fur Eanh\.luakr KC'~I'lan1 DC'!JI~n ttf COnl,:fCll' Cira"ll~ [)am, '"'~ rf'"\'C"1o (j and Chopra. ,I\, ~. Junt,' 1~~6. (PR~7

1~4 160,SIAU8

l'CB'EERC-85.11 -DynamIC Inlorawon Eff<cI' ,n Arth [lam, hy nough. R W. Chang. K·L Chro. H'l) .nd lihana'i. Y Orwo<' 1~~5. ,l'lIh61350c7, ..SIAUl

lTB!EERC-S5i13

l'CBIEERC-8SI14

l'CB'EERCoSI/I I

l'ClliEERC-86JO\

UCB/EERC-86/0~

l'CB:EERC-86IOJ

l"B/EERC-86104

UCBIEERC·S610\

lTB/EERC-86/06

I'CB/HRC·86/07

tiCB/EERC-86/0S

UCBiEERC·S6/09

llCB/EERC-86/ I0

UCB/EERC·S6/11

UCB!EERC-S61 IC

lTBIEERC·87/01

UCB:EERC-S7/02

lICBiEERC-87/03

UCB/EERC·87104

UCB/EERC·87/01

UCB/EERC·87/06

UCB/EERC-87107

VCBlf[RC.S7/08

VCBlEERC-87109

VCIliEERC.S7110

VCBIEERC-8711 I

UCIliEERC-87112

UCBJEERC.I7.'1 J

VCS/EERe-8711.

UC8IEERC-87/15

UC8IEERC-87116

DynamIC Rnpon\C of Long Valle' Dam," lhe Mammolh uke Earthquake Sene. of Mal ~1·~7. IUXO: b, UL S and Seed. H B.No\.mb<r 1985.IPB86 14cJ04, ...SIA05

'01. Mr1hodalagy for Camput..·.A,d.d Dt$Il\n of E,nhqu.ke·Re"".nt Sled StruClure,. by,",u'tlO. M..... PISI... K.S and Mahon. SA.DtCtmbtr lu85.IPB86 15948a/ASI..~1O

'RC'5pon~ of Tenslon·LeI. Platforms to Vrnlca! ~I'!iml{" EJ.tltatlOn~: h~ LlOu. G.-S.. Pt'nzlen. J. and Yeung. R\\' .. Oecrmbf'r 19H~.

(PB87 114 k711,",SIA08

·C\chc loadanc. Tests of Masonry SlngJr PI~n.: Volume' 4 - ..4"ddltlonal Tt!»(!» "'Ifh H~lght 10 \\"jdth RaffO of J _- b-~ S\'clnS~(m, B..MeNn·... H D and Sueuoglu. H.. Dtctmbtr IUk5

·"'n Ea.pcnmcntal Proaram for Studying thr D~'namlc R('~ponS(' of a ~l('cl Framr wI1h a vant'ty of Infill Panlllon~_· h~ "t anp. B. andMeN"en. H n. Dtctmbtr 198~. (PB90 2b~ 676',\05.

-.. Stud) ~f Se"mlC.lI~ R."Slanl Eectnlne.lI) Braced S..d Erame Sy'lem,.' by Ka",1. K. and Papo\. LP. Janu.!) 1986.II'B87 Ic4P8 1 ASI,",14

'1)e",n Problem, ,n SOIl L,quef.ClIon: b) Sted. H.B .. r.brual) 1~8(). ,PBP I"~ 1861"'S,,",U.1.

Jmphcauons of R«,ent E.a:rthqu.ake!i and Rt'search on Eanhquake-Rt'!loJilan! DriJ~n and Con!tlruC1Jon of Bulldlngs.,· b\ Btnt'f,'. \' V..March 1986. (PBK7 124 194''''S.,",05

'The tIl< of Load D'pC'ndenl \'relof' for llyn.mll' .nd E.nhqu.ke Analys.,,: b~ Ltl", p. W,lson. ELand C'I~ulh. R W . M.rrh1986.II'B87 124 ~O"JASIA I~

-Two Beam·Ta-Column W.b ("onn<Cllon>: by T..1. K·C and Popo". E.P Apr,1 1986. (pB87 124 .101IASI...04.

"[)etcrmlnatlon of Penetration Resls1ance for Coa~-Gralncd Solis uSing the hecker Hammer Dnll. b~ Hard~r. LF and Scrd. II.B.,May 1'186. (PBS7 1~4 cIOIAS)A07

." Mathrmallcal Modtl for Prtdlctlng Ihe.- Nonhm:ar R~sponsc of Unrelnforced MaSl\n~ Walls to In-Plane Eanhqualt" E:\C1tatlon!o. t'!~

Mengl. Y .nd Me!':,,·en. H.D .. Ma, IQ86. (PB87 124 7S0,ASI ..06

'The 19 Seplember 1985 M...eo Eanhqu.h Bul1dmllkha',or: ,,, Bentro. VY. July IQ86

·EACD·1D:A, Compul., PrOl\ram for Thr~.·Dlmen"onal Eanhqu.ke"n.I~S1s of Conerel< Dams: by Fak. K-1. Hall. JF. andChapr......K" July 19k6 (PB87 124 2281...SI,",08.

-Eanhquak. S,mul.lIon T.-IS and A.soclaltd Stud,.. of a a.J·Seale Model of • SI~,Slory ('onctnlneall} Rraced S..el Structure. byVane. C·M. and Btnero, V. V.. Dteembtr 1986. /PB87 )6J 164I.AS)AI7.

'Mtchamral Ch.raclem..cs of Ba.. lsolallon B..nng. for a Bridge Dtcl Model Ttsl: by K.h. J.M" Bueklr. LG and Koh. C·G .Nov.mb<r 1987, (PB90 2b2 6681...04.

'Efreel' of A..al Load on EI"lom.ne lso/allon B.anngs,' by Kah. C -G. and K~"l'. J.M .. Novemhcr 1987.

'The FPS Eanbquako R.slSlln, SyS1em' ExpC'nm.nlal R.port: by Zaya,. V.A.. Low. S.S. and Mabin. S."'.. Jun< 19S7

·Eanbquak. Simulalor Ttl.. and A"oclal.d Slud,., of. O.3-Scale Model of. Si,·SIDl) Ece"ln,ally Braced ~,eel Strucwre: by' WhIl·lak.., A., Uang, C·M. and B.nera. V.V.. July 1987.

-A D"placcmtnl Control and Uphft R~slraJnI DtvlC~ for Ba..·lsolaltd 51",elU"': by Kdly, J.M., Gnftilh. M.e an,1 "',ken. 1.0......pol198'

·E.nhqu.k. S,mulalar T.,llng of a CambJntd Slidlnl Ilca"ng and Rubbtr Beanng lsolalion Sysl.m: hI Krll). 1M. and Ch.lhoub.M.S.. 1987.

'Thre.·DlmtnSlonallntiaslic Analysi. of R.mforctd Callerel. Frame-Wall Struetur..: by Mo.zum•. S. and Btnera. \. V. Ma~ 1987.

-Ex!" nm.." on Eccenlrically Ilractd Fram.s With CompoSiI. Floors: by Riel... J. and Popo'·. E.. Junt 1987.

'Dyname Analysis of xl$m,cally Resistant Ecctntneall) Braced Frames: b) R,eI.s. J. and Popov. E.. Jun. 1~g7.

-Undrail'td Cyclic Tria..a' Teslin. of Gra••ls-Th. ElrtCI of M.mbrant Comphanct,' by Evans, M.D. and xed. H.B Jull' 1987.

'H,bnd s...lullon Terhmqu.. for Gtnerahz.d ps<udo-DynamlC T..llnl: by Thewalt. C. and Mahin. S.A., July 1987.

-Ultimale BehaVior of BUll W.ldtd Sphe.. In Hnvy Rall.d St.<I Stellons: by Brunt.u. M.. Mahin. SA. and Popov. [I'.. Septembtr1987.

-Residua' S1ltn8th of ~nd lrom Dam Fallurts m Ihc Chlltan Eanhq"".e of March J. 1985: by 0. Alba. 1'.. Stro. H B. Retamal. Eand Sttd. R.B.. Stpl.moo 1987.

'IntlasliC xlSmlc Re$pons< of SlruClUr-. "lIh Mu, or Stiffness Ee«nlnc,"" In Plan: by Bruntau. M .nd M.hln. S.."-.. StpI.mbcr1987. (PB90 262 650)'\ 14.

"('STRlICT: An Inleracliv. Compul.. Environmtnl for Ih. Dt$'JIl and Analy$!$ of Eanhquak. R'$!Slant SI.<I Struclur..: by' ....u'lon,M.A.. Mahin. S.A. ane! P"te•• 1\..5.. xpt.mber 1987.

'Expenmenlal Stud" of Reinforced Coner,,'. Column. Sub,ffled 10 Mulh-Allal Loadml. - by La",. 5.5. and Mothlt. J.p.. Stpltmbtr1987.

·R.lallonsblps btl_n Soil Cundillan. and I:.arthquak. Ground Motion, in MulCo elly in Ih. Eanhquak. of Xpt 19, 1985.- by s..d,H.B.. Romo. M.P" SlIn. J.• Jaime, A. and lysin'" 1.. Octobtr 1987.

-E.",nmtn..1Study of Sti.mlC Rnpon~ of R. C xlback BUlldln,s: by Shahrooz. B. M. and Moth!•. J.1'.. Oclaber 19S7.

-171-

l'CB'EER(,·88/0~

l'("BEFRC·8g '05

llC B/EERC-89111

l;(,8/EERC-89' I0

'Thr Eff<Cl of Slab, on Ihe Fle,ur.1 Reh., 1<" of Ream,: by Panl.1oJ'Oulou. SJ and Morhle. J P . OClohrr 19S7. (PB90 ~6~ 7001",07.

D..lgn Pr<x-rdurc for I(·FBI Be.nng, hy Mmlaglld. Nand Krlly. 1M. No'ember If/P. (PBW J6: 7/8IA04

"n.lyll<·.1 Mode" fur PrcdlClInS ,he un..al Re,pon!>< of R (' Shear W.II, £>.I ...llon of Ihelr Rehab,hly: by Vukano. A and Ber-tcro. \,.\'" !\:o"'C'm~r IQg~

'Earthquake R.-ponse of Tors,onally-Coupled BUIlding,: by He)al. Rand Chopl •• ".K.. Otctml><r 1987.

'[hnamlc Re-""i<'" InleraCllon "Ilh Monllerllo ()am: by Clough. RW .. Ghana.l. Y, and Q,u. X-F .. Drccmbtr 1917.

'Suength E'alu""," ofCoar><·(jralOed So,!,: by S,ddlql. F.H .. S«d. R.B. Chan. C.K.. Seed. H.B .nd Pyle. RM. December 1987.

'Se"mlc Reha"or of Conetnlnc.lly Braced <;Itel Frame.: b) Khallb. I. MahIO. S."'. and Plsler. K.5.. Janua') 1918

·E>pcnm.ntal halu,"on of Se"m,c 1""latlon of M.dlUm·R"e Slrueturt> SubJcctlo Uphn: by Gnllilh. M C. K.lly. J.M.. Co\enC).V .....nd Koh. C G. J.nua" 19S8

(',dIC' Reha' ,or of Sleel Double "np.le Connecllon>: by ...".n.h-....I..... and Nader. M.N.. J.nu,!) 1988

·Re-nalu.llon of the Shd. In Ih. Lower San F.rnando Dam m Ih. Earthquake of Feb. 9. 1971: by Seed. H.B.. Se.d. R.B.. Hardrr.l F and J"n8. H.·L ",pnl 1988

-[,prnmrntal halu,""n of Sc:"mIC 1""lallon of a :"me·510"· Brac.d SI.el Fram. Subject 10 llphft: by Gnffilh. M C. K.II). J.M andAiken. ID. May 1988

·DR.... IS-~DX I 'srr ('u,dr.' h, Allahabld.. R .nd Powtll. GH .. Marrh 1988.

. Thearrllc.1 and Expenmental Stud.., of CyllRdnc.1 Wotrr Tank. ,n Basr·lsolaled SlruC1U~S: by Cbalhoub. M.S. and Krlly·. J.M ..",pnl 1988

· An.I)", of N.ar-Source W .... Scp.rallon ofW.\,e Type, usmg Suong Mallon Array R.<ordonll': by DarraJit. R B.. June 1988.

· Aluma",•• '0 Srand.rd Mode SUP<'rpo'/l,on for An.ly·... of 1'Oon·O...".lIy Damped SySlems: by "usa,no\'. A...... and Clough, R.W ..June IQHS

-The land.llde a' the Port of :>lIe< on OClober 16. 1979: by Seed. H.B.. S.ed. RB. Schlo...r. F.. Bloodeau. F. and Juran. I.. Jun.1.~8

'L,quefactlon POleollal ofS.nd Drpo"t> Under Lo.. Le'elsofExCll.llon: by C.rter. D.P.•nd S«d. H.B.. Augustl9S8.

'Nonhnear .... n.ly'" of R.1Rfore<d Conc«" Fram•• Under Cy'cllc lo.d Re\'ersals.· by FlllpPOu. F.C and Is... A.. September J988

'Impll,""oo> of Recorded Eartbqu.ke Grouod Mol'ons on SeISmIC Dr,'gn of Buildonl Slru(\u...: by Uanl- CoM. and Bert.ro. V.V ..!';o'emht'r I QK8

An F'I'<"menl.1 <;IUo) of Ihe Beh.'.or of Du.1 Slr.1 S'sltms.· by Whm.ker......S.• V.ne. CoM. and Bertero. V.V .. Seplember 1988.

'D,n.m" Modul. and Dampmg Rallos for Cohe,,,c 5011.: by Sun. J.I .. Gol.sorkh •. R. and Seed. H.B .. AUlust 1988

'R.1Rforced Connele Fla. PI.le, Under lal"al load: "'n ExP<'nmenl.1 Slud) Includ,ng B'3<,.1 Effeels: by P.n. A~ .nd MOtble. LOrlobtr 1988.

Eanhquake Englnemng Rese.rch .t Berk.lrl - 1088: by EERe No..mber 1988.

-Use of Energ' as a DrSlgn Cntrnon on E.rthquake-Remt.n, Dt-S1gn: b) Vang. C.-M. and &rtero. V.V .. Nov.mber 1988.

'Sltel Beam-Column JOInIS '" SeISmIC Momenl ReslSllng Fr.mes: by 1'58.. K.-C and Popo,. F.P.. No\'ember 19SB.

-B... I\olallon 'n Japan. 1988: hI K.lI,·. J.M. De:cember 1988.

'Ben.nor of Long links 10 EceeMne.lI) Braced Fr.m..: b) Enldhardl. M.D. and Popo\'. EP.. January 1989.

·Eanhqu.ke Simulator T,,,,"g of 5,«1 Plat. Added DampIng and SlIlfne.. Elemenls: by Whlllakcr. A.. Bertero. VV .. "IOn5O. J. andThompson. e. Janu.!) 1989.

-Impllc.llon, of SlIr Effect> In Ihe Me..c~ CII) E.rtbQuake of SePI. 19. 1985 for Earthquake.Remlan' Dt-s'ln Cnlena in Ihe San Fran-CISCO Ba) Area of ("ahfornla: by Seed. HB.•nd Sun. JI.. M.rcb 1989.

· Earthqu.ke "'0.1,'''' .nd Response of Inl.ke-Oulltl Towers: by Goyal. "'. and Chopra......K.. July 1989.

·Th. 1085 Ch,l. E.nhqu.k.: An E\,.lu.llon of Slruc, ural R.qulrem.nt, for B••nng W.II Butldonll': by Wallace. JW. and Moeble.Jp._ July 1989.

'EIfeclS of Sp.ual Vanallon of Ground Mol,ons on large Muluply·Supported Slructures. - by Hao. H.. July 1919,

·E ..D-\p· Enhanced Arch D.m Analy.is Program: V..rs·s Manu.l: by Gbanlll. Y. and Clough. R.W .. AUIUSI1989.

-SelSm,c Performance of 51eel Moment Frames Plasucall) Drs,gned by Least Squares 51=. fields: by Obi. K. and Mahin. S.A..Augu.1 1989.

'Fea..b,IIt) .nd Perform.nce StudIes on Impro"ing Ibe Earthquake ResiSlan« of New and ExlSl,ng Buildings VSlng lb. Fncllon Pendu·lum SHlem: by Zay.s. V.. low. S.. M.b,n. SA and BOllO. l .. July 1989.

'Mea,ur.men, .nd Ehmmallon or Membrane Comph.nce Elf-'ls m UndralRed Tna"al Testin.: b~' Niebolson. I' G.. Seed. R.B.•ndAn,,·ar. H.. s.,plcmber 198f/.

'SI.IIC 1',11 Beba\'lOr of linanchored Cyllndncal Tanh.' bylau. D.T.•nd Clough. R.W.• Seplrm~r 1919.

-AD.... p·88: A Compuler P,oBram for Nonhne.r E.nbquake ."nalysis of Concrete Arch Dams: by Fen\'es. G.L. MOJlabed,. S. and Reimer. R.II. Scpl<mber 1989.

IJCBIEERC·R9113 -Mech.nlC' or lo.. ~h.pc Faclor Elaslomene SeISmIC Isol" 'Bearings: by Aiken. 1.0.. Kelly. J.M. and raj;na•• F.F.. November1989.

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-172·

'EApcnmcnraJ Studies of a SIO~I~ Sto~ Srt't"! Siructurt It"slC'd -'llh FI~(Od. St'ml·RJ,ld and tlf'uhlr ConnCCllon~: 0) !Sadrr, \t.N. and"'Sllnth·....I....."u~u'l 1~8Q

'Collaps< of Ih. CH"'" Strtt' VIaduct "' I R..ult of the Lorn. Plltll Earthquak.,- b) N,m,. D.K. P.llranda. [",k.n. ID.. Wh,ttakt!, ....S and 8tn.ro, V\' .. No'tmber 1'189.

·Mrchame. of Htch-Shapr Factor EI..lom.nc St"m,c hol.llon Branng." ~~ K.U). J M. "'Iktn. 1.0 and TaJlllan. fF. March 19'10

'Ja'·,d·s Paradox Th.lnOu.n« of Prtfonn on Ih. Mod•• of V,hratmg !kam.'~) 1'(11). J.M. Sackman, J.L. Ind )a,'d ..... Ma) 1'190

'Eanhquak. S,mulator TMttn& and "'nll~llCal Slud,es of Two En.rgy-...bsorbtnl Sy...m. for MulhSlol") Struetur.... ~)",k.n. I D andK.lly. JM., October 1990

'Dlmage '0 the San Franc.sto-Oaldand 81) Bndll' Dunn.th. October 17.1989 Eanhquak.: hy""an.h. ". Jun. 1990

'Prrl,mtnary R.pon on th. PnnClpl1 Grolrchftlcal ....pec.. of Ih. Oclober 17. 1'18'1 Lorna Pn.la Eanhquak• .- b) Sr.d. R B. DlCk.n·wn. SE.. R,.m.r. MF. Bray. J.O.. SlIar. N.. Mllchell. J.K.. Id"". 1.1'.1 .. Kay.n. RE. Kropp.." .. Hardt!. L.F.. Jr and Pow... M.S."pnl 1990.

'Mod.Is of Cn..ca! ROIlon. In R"nforcod Conertt. Frames Under SeISmIC E""ll1om: b) Zulfiqar. N. and F,ltppou. F.. 1'.11) 19'10

'.-\ Unlfi.d Eanhquak•.Re...lanl DeSlpl Melhod for St..,1 Fram•• U..nJ ARM' Mod.ls" by Takewlkt. J.. Coni•. J.P. Mah,n. SA andPuter. K.S.. June 1990.

'Soll Condl\lons and Eanhquak. Hazard Mlllpllon 1ft th. Manna OlSlncl of San f,anClsco: by Mllchrll. J.K. Ma>OO<l. T.. Kay.n.RE. and Seed. R.B .. Mal' 1990

-lnOu.nc. of Ihe E.anhquak. Ground Mo..on Proco.. and StruClural Propen••, un Rosponso Charact.mllcs of S,mple Structur••,' byConte. I.P.. PmOl. K.S. and Mlhln, S." .. lui)' 19'10.

-bpenmental T....n. orlh. R.S1b.nl-Fnc..on 8aso 1",lallon S)'".m: br Clark, P.W. and K.lly. J.M .. Jul) 1990

'Scumoc Hazard "naIY.I.: Improved Mod.I•. Une.rta,nll.. and Srnlll1Y'..... • by Maya. R. and Der Kluregillan, ..... March 1988.

-Elfe." of Torsion on th. LIReir and Nonhnear Srtsmoc Response of Struetur..: by Srduat. H. Ind BmOlo. V. \'.. Srpl.mber 1989.

'Tht Elfrct. of Toctonic Movements on Stresse. and Deformallon. In Eanh Embankm.n••: by Bra). J. D.. Seed. R. B and Seed. H. B..Srptember 1989.

'Inelasltc SelSm.c Respon.. ofOn.-Stol)·. Asymm..lnc.Plan SySlems: by Gool. R.K. and Chopra. ".K. Oclober 19'10.

'DynamlC Crack PropaplIon: A Mod.l for N.ar·Fleld Ground Molton.: b)' Sryy.d...n. H. and K.lly. J.M. 1'190

-Srnsllivlly of Long.p.nod R..ponse Spectra to System Inillal CondItion,: br Bla>quez, R.. Venlura. C and Krll)'. J.M .. !'I~O.

'BoblvtOr of Peak Valu.. and Spectral Ordmales of Near-Source SI"ong Ground-MollOn ov.r a Dense AlTa,. - by N,all. M.. Jun. 1990.

'Malenal Chara.tenzallon of ElaSlomen used In Eanhquake Base "olat,on: by Papouh•. K.D. and K.lly, J.M.. 19'10.

'Cychc 8thavior ofSt..1 'lop-and-Bonom Pial. Moment Conn.d.ons: by Harrioll, 1.0. and " ...n.h. A.. Au,usl 1990.

'Srtsmic Response Evaluallon of an In.trum.nt.d S" SIOr) St..1Buildinc.· br Sh.n. J.,H. and ASlanoh. " .. Dr<-ombor 1990.

'Observations and Imphcat.ons of Trsts on the Cypress Stlttl V,aduc1 Tnt SINdure: by Bolla. M., Mlbln. S.." .. Moehl., I.P.St.phon. R.M. and Q,. X .. Doc.mber 1990.

-EJ<pOnmental E"aluallon of Nillnol for EnelJY D,ss,pahon in Suuetur..: by Nlms. OX.. Sasaki. K.K. Ind Kelly. J .1'.1 .. 1991.

·D..placrm.nl lkslgll Approach for Reinforcrd Concrelt Struclur.. SubJect.d 10 Earthquake.: by Q•• X. and Mcohle. I.P.. January1991.

'Shake Table Test. of Lonl P.nod Isolation Syst.m for Nuclear F••tlil;e, al Soft Sool 5,1..: ,,~ K.II~. J.M .• March 1991.

·Oynami. and failure Chancl.mlies of Brid&eston.lsolaIlQn lkarinp: by Kelly. J.M.. April 19'11.

'Base Shd,n. R..ponse of Concrete Gravity Dam. 10 Eanhqual.es: by Chopra, A.K. and Zhang. L. Ma)' 1991.

'Computalion of Spatially Varyin. Ground Mol,on and Foundallon.Rock Impedance Matnces for Se,smlC "naly... or Mch Dam.: byZhan&, L. and Chopra. A.K.. May 1'191.

'E$timauon of Seismic Soure. Processes UStn& Stron. MOllon "rray 0 ..1: by Ch,OIl. S.-J .. luly 1991.

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