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Dan Abrams + Magenes Course on Masonry
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Masonry Structures, lesson 11 slide 1
Seismic Design and Assessment ofMasonry Structures
Seismic Design and Assessment ofMasonry Structures
Lesson 11: Performance-Based Seismic Evaluation and Rehabilitation of
Masonry Buildings
Notes Prepared by:Daniel P. Abrams
Willett Professor of Civil EngineeringUniversity of Illinois at Urbana-Champaign
October 25, 2004
Masonry Structures, lesson 11 slide 2
NEHRP Guidelines
first national consensus document for rehabilitationperformance-based designductility-based rehabilitationdisplacement-based analyses
For free copy of FEMA 356 call:1-800-480-2520
FEMA 273, FEMA 356
Masonry Structures, lesson 11 slide 3
Performance Based Rehabilitation
costbasic safety objectives
probability ofexceedance in 50 years
increasingreliability
2%10%
20%50%
increasingperformance
collapse
life safety
immediate occupancy
operability
Masonry Structures, lesson 11 slide 4
NEHRP Provisions and Guidelines
Seismic Hazard Maps
Sa
T0.2To To 1.0
Masonry Structures, lesson 11 slide 5
Scope of Masonry Chapter
Existing, rehabilitated or new masonry lateral-force resisting elements.Clay and concrete masonry, hollow clay tileUnreinforced and reinforced masonry.In-plane and out-of-plane elements.See Simplified Rehabilitation or Nonstructural chapters for parapets, cladding or partition walls.
Masonry Structures, lesson 11 slide 6
Performance of Brick Veneer
brick veneer
Masonry Structures, lesson 11 slide 7
Masonry Partition Walls
Masonry Structures, lesson 11 slide 8
Contents MitigationABC Good Morning America
Masonry Structures, lesson 11 slide 9
Immediate Occupancy
IO
0.0
0.5
1.0
0.25 0.50 0.75 1.00
First Story Drift, %
Bas
e Sh
ear /
Wei
ght
1.5
Masonry Structures, lesson 11 slide 10
Life Safety
IO
0.0
0.5
1.0
0.25 0.50 0.75 1.00
First Story Drift, %
Bas
e Sh
ear /
Wei
ght
1.5
LS
Masonry Structures, lesson 11 slide 11
Collapse Prevention
CPIO
0.0
0.5
1.0
0.25 0.50 0.75 1.00
First Story Drift, %
Bas
e Sh
ear /
Wei
ght
1.5
LS
Masonry Structures, lesson 11 slide 12
Performance Indices for Masonry
Immediate Occupancy
minor cracks 0.1%
Life Safety extensive cracksno dislodgment of units
0.3%
Collapse Prevention
extensive cracksdislodgment of unitsnoticeable offsets
0.4%
wall drift levels*expected damage
dam
age
cont
rol
limite
d sa
fety
* with bed-joint sliding mechanism
Masonry Structures, lesson 11 slide 13
Enhancement Options
infilled openingsenlarged openingsshotcrete
Masonry Structures, lesson 11 slide 14
Enhancement Options
repointingbraced and stiffened wallsgrouted collar jointsreinforced cores
surface coatings
prestressed cores
Masonry Structures, lesson 11 slide 15
Behavior of Non-Retrofitted Pier
Masonry Structures, lesson 11 slide 16
Ferrocement Surface Coating
Masonry Structures, lesson 11 slide 17
Fiber Reinforced Polymer
Masonry Structures, lesson 11 slide 18
Reinforced Shotcrete
Masonry Structures, lesson 11 slide 19
Reinforced Cores
#3 or #5 bar
-10
-8
-6
-4
-2
0
2
4
6
8
-3 -2 -1 0 1 2 3Drift %
Late
ral L
oad
[kip
s]
8F7F1F
Masonry Structures, lesson 11 slide 20
Reticulated Reinforcement
Masonry Structures, lesson 11 slide 21
Reticulated Reinforcement
Displacement
Forc
e
Masonry Structures, lesson 11 slide 22
Analysis Procedures
Linear Static ProcedureNonlinear Static ProcedureLinear Dynamic ProcedureNonlinear Dynamic Procedure
Masonry Structures, lesson 11 slide 23
Linear Static Procedure
V=C1C2C3SaW
C1= interpolate between 1.0 and 1.5 for T=0.1 and To
C2= from Table 3-1 for framing type 1C3= 1.0 for non-bearing wallSa = spectral accelerationW = weight of building
Masonry Structures, lesson 11 slide 24
Forc
e
Deflection
Linear Static Procedure – FEMA 356
QCE
k
∆y
kQCE
y =∆
∆i
y
iim
∆∆
=
Vb
ECE QQm ≥κ
QCE
QE
∆y ∆i
io = immediate occupancyls = life safetycp= collapse prevention
Masonry Structures, lesson 11 slide 25
Bed-Joint Sliding
Deformation-controlled action
nmebjs AvV =
Vbjs
ECE QQm ≥κ
expected strength
Masonry Structures, lesson 11 slide 26
Rocking
Deformation-controlled action PCE
L
h
Vr
⎟⎠⎞
⎜⎝⎛=
hLP9.0V CEr α
ECE QQm ≥κ
PCE
L
h
Vr
Masonry Structures, lesson 11 slide 27
LSP Acceptability Criteria
(Multiply m factors by 2 for secondary elements for Life Safety (LS) and Collapse Prevention (CP))
EUDCE QQQm =≥κ
Bed-joint sliding 1 3 4
m factors for primary elementsIO LS CP
Rocking 1.5 heff/L>1 3.0 heff/L>1 4.0heff/L>1
Masonry Structures, lesson 11 slide 28
Force-controlled action
Diagonal Tension
00.1hL0.67 for <<
dt
andtdt 'f
f1hLA'fV +⎟⎠⎞
⎜⎝⎛=
VdtP = faA
ECE QQm ≥κ
lower bound value
Masonry Structures, lesson 11 slide 29
Toe Crushing
Force-controlled action
⎟⎟⎠
⎞⎜⎜⎝
⎛−⎟
⎠⎞
⎜⎝⎛=
m
aCLtc 'f7.0
f1hLPV α
VtcPCL
ECE QQm ≥κ
lower bound value
Masonry Structures, lesson 11 slide 30
Modeling and Acceptability Criteria
drift
forc
e CP
d
e
cCP
LS
0.75d
LS0.75e
primary walls
secondary walls
Nonlinear Static Procedure
Masonry Structures, lesson 11 slide 31
NSP: Acceptable Drifts
(Multiply drifts by 2 for secondary elements for LS and CP)
IO LS CP
Drifts for Primary Elements
Bed-Joint Sliding 0.1% 0.3% 0.4%
Rocking 0.1% 0.3 heff/L% 0.4 heff/L%
Masonry Structures, lesson 11 slide 32
Example Building
• URM clay-unit masonry• two-wythe brick walls• constructed prior to 1960• located in St. Louis• total roof dead load = 60 kips• symmetrical structure• soil class B• case A: no testing, visual exam• case B: testing and inspection
Problem: check adequacy of pier for BSO and suggest
rehabilitation scheme if necessary.
Problem: check adequacy of pier for BSO and suggest
rehabilitation scheme if necessary.
URM pier
32’-0”24’-0”
4’-0”
4’-0”
8’-0”
4’-0” wood roof joists
URM bearing wall
7.63”
direction of earthquake
Masonry Structures, lesson 11 slide 33
1.0
1
1v
1
1Xa B
SFBSS ==
Seismic Demand: LSP
Sa
T
S
1
1Sa
S1vo S
SBSFBSFT ==
To
S
Sa
S
XSa B
SFBSS ==
Fa= Fv= 1 for site class B
BS = B1 = 1 for 5% damping 0.2To
Masonry Structures, lesson 11 slide 34
Seismic Demand: LSP
S1 SS To C1 C2 C3 Sa V/W
St. Louis
seconds 129.0)feet12(020.0hCT 43
43
t ===
BSE-1 10% /50 yearsLife Safety
BSE-22% /50 yearsCollapse Prevention
0.05g 0.18g 0.278 1.42 1.30 1.00 0.18g 0.332sec.
0.18g 0.58g 0.310 1.43 1.50 1.00 0.58g 1.244sec.
Masonry Structures, lesson 11 slide 35
Lateral Force Distribution
8’-0”
4’-0”
30.0 + 2(31.8/4) = 45.910.6
5.4
Weights (kips)
total weight per shear wall = 61.9 kips
60.0 kips
31.8 kips
10.6 kips
2.7 kips
2.7 kips
Masonry Structures, lesson 11 slide 36
Pier Strength: Case A, no tests
governs
Vme= 27psi f’me= 900 psi from default values
kips89.9)"48x"63.7)(ksi027.0(AvV nmebjs ===bed-joint sliding:
kips38.2)5.0)(kips29.5)(0.1(9.0hLP9.0Veff
CEr ==⎟⎟⎠
⎞⎜⎜⎝
⎛α=
rocking:
psi4.14)"48("63.7
lbs5290fa == psi5636.1
f'f mem ==
kips54.2)563(7.0
4.141)5.0)(kips29.5)(0.1('f7.0
f1hLPV
m
a
effCLtc =⎟⎟
⎠
⎞⎜⎜⎝
⎛−=⎟⎟
⎠
⎞⎜⎜⎝
⎛−⎟⎟
⎠
⎞⎜⎜⎝
⎛α=
toe crushing:
PG = 5.29k
QCE
8’-0”
4’-0”
Masonry Structures, lesson 11 slide 37
Pier Strength: Case B
Vte = 150 psi from shove tests f’me = 2000 psi from prism tests
kips2.23)"48x"63.7)(ksi0635.0(AvV nmebjs ===
bed-joint sliding:
kips38.2)5.0)(kips29.5)(0.1(9.0hLP9.0Veff
CEr ==⎟⎟⎠
⎞⎜⎜⎝
⎛α=
rocking:
kips60.2)1250(7.0
4.141)5.0)(kips29.5)(0.1('f7.0
f1hLPV
m
a
effCLtc =⎟⎟
⎠
⎞⎜⎜⎝
⎛−=⎟⎟
⎠
⎞⎜⎜⎝
⎛−⎟⎟
⎠
⎞⎜⎜⎝
⎛α=
toe crushing:
psi5.635.1
)psi4.14psi150x75.0(75.0vme =+
=PG = 5.29k
QCE
8’-0”
4’-0”
governs
Masonry Structures, lesson 11 slide 38
Acceptability Criteria UDCE QQm ≥κ
Case A:ok kips3.10kips7.10)kips38.2)(75.0(6Qm CE >==κ
Case B:ok kips3.10kips3.14)kips38.2)(00.1(6Qm CE >==κ
kips3.10)5.0)(kips9.61(332.0QUD ==BSE-1
m = 6 for Life Safety
Masonry Structures, lesson 11 slide 39
Acceptability CriteriaUDCE QQm ≥κ
BSE-2 kips5.38)5.0)(kips9.61(244.1QUD ==
m = 8 for Collapse Prevention
Case A:NG kips5.38kips3.14)kips38.2)(75.0(8Qm CE <==κ
Case B:NG kips5.38kips0.19)kips38.2)(00.1(8Qm CE <==κ
Masonry Structures, lesson 11 slide 40
Rehabilitation Option 1
Enlarge pier width:
'8.10)'0.4(3.145.38L ==
Case A, Check CP:ok kips5.38)kips43.6)(75.0(8Qm CE ==κ
5’-5”
QCE
new
PG = 5.29k
8’-0”
4’-0”old
(Eq. 7-4)
kips43.6
)'0.8'8.10)(kips29.5)(0.1(9.0
hLP9.0Veff
CEr
=
=
⎟⎟⎠
⎞⎜⎜⎝
⎛= α
Check:
Masonry Structures, lesson 11 slide 41
Rehabilitation Option 2
Prestress pier:
kips24.14)kips29.5(3.145.38P ==
Required prestressing force = 14.24 - 5.29 = 8.95 kips
PG = 5.29k
8’-0”
4’-0”
Pstress = 8.95k
Case A, Check CP:ok kips5.38)kips41.6)(75.0(8Qm CE ==κ
(Eq. 7-4)
kips41.6)5.0)(kips24.14)(0.1(9.0
hLP9.0Veff
CEr
==
⎟⎟⎠
⎞⎜⎜⎝
⎛= αCheck:
Masonry Structures, lesson 11 slide 42
Rehabilitation Option 3
Reinforce:
Consider as reinforced masonry pierper Sec. 7.4.4 8’-0”
4’-0”
2 - No. 4 bars
Masonry Structures, lesson 11 slide 43
Damage to Out-of-Plane Walls
1886 EarthquakeCharleston, South Carolina
1994 Northridge Earthquake, Hollywood
Masonry Structures, lesson 11 slide 44
Out-of-Plane Walls
Flexural cracking limits IODynamic stability for LS and CP
1-story bldgs 20 16 13
Pk
multistory bldgs1st story 20 18 15top story 14 14 9
all other walls 20 16 13
dynamic stability ok if h/t < table values
Wall types SX1 < 0.24g 0.24g < SX1<0.37g 0.37g<SX1<0.5g
Masonry Structures, lesson 11 slide 45
Masonry Infills
URM Infill, Tangshan, PRC URM Infill, Campania, Italy
Masonry Structures, lesson 11 slide 46
Masonry Infills
Static Cyclic Tests of URM infillsUniversity of Illinois
-300
-200
-100
0
100
200
300
-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3
Lateral Drift, %
Infil
l She
ar S
tres
s, p
siIn
fill S
hear
Str
ess,
psi
Lateral Drift, %
Masonry Structures, lesson 11 slide 47
Infill Damage Patterns
crack pattern, large-scale static test
crack pattern, half-scale dynamic test
Masonry Structures, lesson 11 slide 48
Frame-Infill Systems
Masonry Structures, lesson 11 slide 49
In-Plane Masonry Infills
Stiffness
H
inf
meinf
rEatk =
a
rinfinf
4.0col1 r)h(175.0a −= λ
41
infcolfe
infme1 hIE4
2sintE⎥⎦
⎤⎢⎣
⎡ θ=λ
Masonry Structures, lesson 11 slide 50
In-Plane Masonry Infills
Strength
vieniineCE fAVQ ==
ECE QQm ≥κ
Masonry Structures, lesson 11 slide 51
m Factors for Masonry Infills
Example:Life Safety
Table 7-6
ine
fre
VV
=β
0.30.7
1.3inf
inf
hL
m
2.0
1.00.5
4.0 6.08.0
3.55.2
7.0
6.03.0 4.5
page 7-20
Masonry Structures, lesson 11 slide 52
Out-of-Plane Infill Strength
Pres
sure
, psf
Center Deflection / Height %
Masonry Structures, lesson 11 slide 53
Out-of-Plane Infills
low moderate highseismicity seismicity seismicity
IO 14 13 8LS 15 14 9CP 16 15 10
Table 7-8: maximum h/t ratios for which no analysis is necessary
Masonry Structures, lesson 11 slide 54
Out-of-Plane Infills
If arching action is prevalent:
CP for 3% andIO for %2
th002.011
th002.0
h 2
inf
inf
inf
inf
inf
inf
<
⎟⎟⎠
⎞⎜⎜⎝
⎛−+
⎟⎟⎠
⎞⎜⎜⎝
⎛
=∆
hinf
∆inf
Masonry Structures, lesson 11 slide 55
Out-of-Plane Infills
If arching action is prevalent:
2.11.7 Sec. per load
144x
th
'f75.0qQ
inf
inf
2minCL
<
⎟⎟⎠
⎞⎜⎜⎝
⎛λ
==
Masonry Structures, lesson 11 slide 56
Undesirable InterventionsMaintain deformation controlled mechanisms
– do not change rocking to shear mechanism with coatings, overlays, shotcrete or reinforcement
– do not change bed-joint sliding to diagonal tension with brittle coatings or overlays
Alter force controlled mechanisms – enlarge openings to promote rocking
– lighten gravity loads to piers to avoid toe compression
Masonry Structures, lesson 11 slide 57
Concluding Remarks
• Systematic rehabilitation of masonry buildings.
• Guidelines are first performance-based provisions for masonry structures.
• Judgement of engineer is essential for proper application of Guidelines.
Masonry Structures, lesson 11 slide 58
Famous Last Words
Infrequent events will not happen tomorrow….
1886 Charleston, South Carolina 2001 Gujarat