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“Investigation of the seismic soil-structure interactionon a concrete instrumented building ”
Teresa Crespellani, Johann Facciorusso, Claudia [email protected]
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
First European Conference onEarthquake Engineering and Seismology
Geneve, 7 sep 2006
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
22//2121
Introduction
11stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
Soil-Structure Interaction (SSI) effects can lead either to seismic actions lower than the free field ones, or to more conservative ones
Considering SSI may be essential for:assuring safety and reliability or reducing repair costs mainly for
historical monuments, public buildings and critical facilities
performing a safe design
A precise prediction of SSI during earthquakes is generally difficult due to several uncertainties affecting:
free-field motion (obtained by a site response analysis as input to SSI)
soil behaviour (of the deposit underlying the structure)
numerical code (adopted to perform SSI analysis)
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
33//2121
Introduction
11stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
A true validation of a computer program must be aimed to test the reliability of the numerical results (by comparing them to real recorded motions during earthquakes) and the capability of the adopted code to model the most important aspects of the SSI at the site.
The first and crucial step consists of choosing the test sites, which must be characterised by:
buildings equipped with several seismic recording instruments
a good knowledge of the properties of soil underlying the structure (behaviour in static and dynamic conditions, depth and thickness of layers, bedrock location, etc.)
a good knowledge of the structure and its dynamical behaviour (modal analysis)
a site seismicity congruent with program capability (i.e. linear or linear equivalent model – low-to-medium seismicity)
Moreover the test site must be representative of many other sites in the region
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
44//2121
SASSI 2000
11stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
SASSI 2000 is a System which performs the Analysis of Soil-Structure Interaction by applying a FINITE ELEMENT METHOD based on SUBSTRUCTURE METHODS
The substructure methods divide the soil-structure system into substructures discretised by finite elements, each of them is solved separately and combined to obtain the complete solution by employing the principle of superposition (hence these methods can handle only linear or equivalent linear properties).
The solutions are obtained in the frequency domain for a certain number of frequencies (15-20) from which the intermediate solutions can be obtained by interpolation
The basic substructure methods adopted by SASSI 2000 are:
the Flexible Volume Method the Subtraction Method
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
55//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
= - +Qb
Flexible Volume Method
Qb
SASSI 2000
( structure+foundation+soil)
Free field siteExcavated soil
(replaced with embedded foundation) Structure(superstructure+foundation)
Boundary nodes
External forces
Nodes at the boundary of the near field zone
Nodes at the interface between the structure and the ground
Nodes within the excavated soil
Interaction nodes
Near field zone
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
66//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
= - +Qb
Subtraction Method
Qb
SASSI 2000
Free field siteExcavated soil
(replaced with embedded foundation) Structure(superstructure+foundation)
Boundary nodes Nodes at the boundary of the near field zone
Nodes at the interface between the structure and the ground
Interaction nodes
External forces( structure+foundation+soil)Near field zone
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
77//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
SASSI 2000
The input motion (or control motion) consists of an arbitrary 3-D superposition of inclined body waves and surface waves and is expressed by a time history acceleration assigned to one of the three directions at a control point
The remaining site (far field) consists of horizontal soil layers overlying a uniform halfspacesimulated by the variable depth method and viscous dashpots.The soil behaviour is assumed to be elastic or viscoelastic and a linear equivalent model is adopted to solve the site response analysis (coupling SASSI 2000 to Proshake).
HALFSPACE
Control point
Near field zone boundary
Hi, γi, VSi, VPi, DSi, DPi
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
88//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
Site selectionS
EIS
MIC
OBSERVATO
RYO
F STRUCTURES
O working systems (1st tranche)O working systems (2nd tranche)O systems under realisation (3rd t.)8 N° of systems in a Region
Italy: 105 build.s10 bridgesin total
1 811
110
694 6
128
o
12 8
o
13
1
4
3o
o
o
o
o
o
12
o
o
oo
SE
ISM
ICO
BSERVATORY
OF STRUCTURES
O working systems (1st tranche)O working systems (2nd tranche)O systems under realisation (3rd t.)8 N° of systems in a Region
Italy: 105 build.s10 bridgesin total
1 811
110
694 6
128
o
12 8
o
13
1
4
3o
o
o
o
o
o
12
o
o
oo
SE
ISM
ICO
BSERVATORY
OF STRUCTURES
O working systems (1st tranche)O working systems (2nd tranche)O systems under realisation (3rd t.)8 N° of systems in a Region
Italy: 105 build.s10 bridgesin total
1 811
110
694 6
128
o
12 8
o
13
1
4
3o
o
o
o
o
o
12
o
o
oo
test site quite representative of many other sites in the region
low to medium seismicitycongruent with program capability (limited to linear domain)
good knowledge of the soil properties and of the dynamical behaviour of the structure
TEST SITE
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
99//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
Soil characterisation
boreholeswells
Selected building
Debris soil
UNIT A
UNIT B
UNIT C
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
1010//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
Soil characterisation and modelling
Halfspace
Viscous dampers
VS (m/s)A
lluvi
al d
epos
itM
arin
e cl
ays
UNIT A and B : clay and silt with fine sand
UNIT C : gravel and gravel with sand and silt
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
1111//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
Soil characterisation and modelling
00.10.20.30.40.50.60.70.80.9
1
0.001 0.01 0.1 1γ (%)
G/G
0
Unit A and B (experimental data)UNIT A and B (regression data)UNIT C (Rollins et al., 1998)
0
10
20
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0.001 0.01 0.1 1γ (%)
D (%
)
Unit A and B (experimental data)UNIT A and B (regression data)UNIT C (Rollins et al., 1998)
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
1212//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
Structure characterisation and modelling
The building examined has a regular compact shape with a rectangular horizontal section. 10 m
11 m
28 m
The structure is composed of a concrete frame with two masonry cement floors respectively at 4.25 m and 8.35 m from ground level with a total thickness of 55 cm.
The foundation system, made up of a system of transversal and longitudinal ground beams, is placed at a depth of 80 cm below ground level and lies on soils belonging to Unit A.
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
1313//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
Structure characterisation and modelling
The foundation system is modelled with (3-D) 8 nodes prismatic elements (solid)
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2 m0 m
423 elements1004 nodes
Unit = cm
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
1414//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
Structure characterisation and modelling
The whole superstructure (beams, columns, infill systems) was modelled by means of 3-D beam elementsThe whole superstructure (beams, columns and infill systems) is modelled by means of 3-D beam elements.
Diagonal weightless rodssimulating infill systems
Beam influence area to assign infill system weight
Node influence area to assign the floor system masses
Type floor system
Type vertical frameDiagonal infinitely rigid weightless rods to riproduce a plane constraint
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
1515//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
Monitoring system and seismic input
The whole superstructure (beams, columns, infill systems) was modelled by means of 3-D beam elements
3
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1 2 1311
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x
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-0.08-0.06-0.04-0.02
00.020.040.060.08
0 5 10 15 20Time (s)
Acc
eler
atio
n (g
)
-0.08-0.06-0.04-0.02
00.020.040.060.08
0 5 10 15 20Time (s)
Acc
eler
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n (
g)
Channel 1 (X-axis)
Channel 2 (Y-axis)
PGA (g)
Channel 1 Channel 2
PGV (mm/s)PGD (mm)Arias Intensity (mm/s)Trifunac duration (s)Predominant period (s)Max spectral acceleration (g)
0.0756 0.038827.98 14.361.86 2.0114.1 7.927.48 10.310.2731 0.24670.187 0.134
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
1616//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
Experimental data and numerical results
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Time (s)Ar
ias
inty
ensi
ty(%
)Ac
cele
ratio
n(g
)
-0.15-0.1
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0.050.1
0.15
0 3 6 9 12 15 18Time (s)
-0.15
-0.1
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-0.050
0.050.1
0.15
0 3 6 9 12 15 18
Acce
lera
tion
(g)
Aria
sin
tyen
sity
(%)
0
25
50
75
100
0 3 6 9 12 15 18Time (s)Time (s)
Acce
lera
tion
(g)
Instrumental recordingsNumerical analyses
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
1717//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
Experimental data and numerical results
3
6
94
5 12
1 2 1311
10
7 8
x
z
y
Time (s)
Aria
sin
tyen
sity
(%)
Aria
sin
tyen
sity
(%)
0.00
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0.02
0.03
0.04
0 5 10 15 20
0
0.1
0.2
0.3
0.4
0 0.5 1 1.5 2 2.5
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0.1
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0 0.5 1 1.5 2 2.5
0.00
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Spec
tral
acce
lera
tion
(g)
Four
ier
ampl
itude
(g*s
)
Period (s)
Frequency (Hz)
Period (s)
Frequency (Hz)
Four
ier
ampl
itude
(g*s
)
Spec
tral
acce
lera
tion
(g)
Instrumental recordingsNumerical analyses
-20-10
0102030
CH 4CH 5CH 7CH 8CH10CH 11CH 12CH 13
∆S A
(%)
020406080
CH 4CH 5CH 7CH 8CH10CH 11CH 12CH 13
∆D
S(%
)UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
1818//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
3
6
94
5 12
1 2 1311
10
7 8
x
z
y
-20-10
010203040
CH 4CH 5CH 7CH 8CH10CH 11CH 12CH 13
∆I A
(%)
Experimental data and numerical results
-10-505
10
CH 4CH 5CH 7CH 8CH10CH 11CH 12CH 13
∆PG
A(%
)
∆X (%) =[X(exp)-X(num)]
X(exp)
-0.10
-0.05
0.00
0.05
0.10
0 6 12 18
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221 222 223
253
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254
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239 240 241
272
242 243
273 275274
244 245
215214213212211210209208207206205
138137136
199198197196195
190 191 192 193 194
178177176175174173172
157 158 159 160 161 162 163
148147146145144143142
141140139
189188187186185184183182181180179
155
171170169168167166165164
149 150 151 152 153 154 156
135134133132131130129128
106105
110 111
127126125124123
107 108 109
104103102
100
120 121 122
10199
119118117
989796
116115114113112
9594939291
908988878685848382818079787776757473727170696867666564636261
605958575655545352515049484645 474443424140393837363534333231
3029282726252423222120191816 171512 14131110987654321
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320
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386385384383
358357356
355354353352
321 322 323 324 327326325
296295294293292291290
260 261 262 263 265264
243242241240239238
229228227226225224223222221220219218 236235234233232231230
211210209208207206205
194193192191190189188
177176175174173172171169 170168167166165164163
152151150149148147146145144143142141140139
360
329
298
267
359
328
297
266
244
237
212
195
178
153
50
247246245
217216215214213
199198197196
179 181180
154 155 156
182
157
200
183
158
201 202 203 204
186185184 187
162161160159
138137136135134133132
128127126125 131130129
124
93
62
3130
61
92
123122
91
60
29
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59
28
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119 120
89
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272625
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53
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114113
82 83
5251
212019
81
112111
80
49
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110
79
48
17
109
78
47
16
108107106105
777574
4443 45 46
15141312
42
104
73
1110
41
72
103102101100
69 70 71
40
9
39
8
38
76
37
68
99
5
36
67
989794 9695
6463 65 66
35
4
343332
321
x
y
2 m
0 m
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
1919//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
Soil-structure interaction effects
Node n° 92
Node n° 78
Node n° 300
Once validated the software, SSI effects at the foundation basement are examined for the selected seismic input.
-0.10
-0.05
0.00
0.05
0.10
0 6 12 18
Free field station
Instrumental recording at the free field (X-direction)
Numerical results at the selected nodes
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
2020//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
Soil-structure interaction effects
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0.1
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0 0.5 1 1.5 2 2.5
Free-fieldnodo 300nodo 92nodo 78
Spec
tral
acce
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(g)
Period (s)
KX =X(node)
X(free-field)
PGA [g] IA [m/s] Td [s] KPGA KIa KTd
Node 92-X 0.0651 0.1 4.88 0.87 0.76 0.65
Node 78-X 0.0608 0.0093 4.53 0.82 0.70 0.60
Node 300-X 0.0633 0.0095 4.62 0.85 0.72 0.62
Node 92-Y 0.0328 0.0046 7.84 0.88 0.63 0.78
Node 78-Y 0.03125 0.0043 7.84 0.84 0.59 0.78
Node 300-Y 0.0315 0.0042 7.84 0.85 0.58 0.78
UNIVERSITA’ DEGLI STUDI DI FIRENZEDIPARTIMENTO DI INGEGNERIA CIVILESezione geotecnica
2121//212111stst European Conference on Earthquake Engineering and SeismologyEuropean Conference on Earthquake Engineering and SeismologySession ES1 Session ES1 –– Geotechnical EngineeringGeotechnical EngineeringInvestigation of the seismic soilInvestigation of the seismic soil--structure interaction on a concrete instrumented buildingstructure interaction on a concrete instrumented building
CONCLUDING REMARKS
The SSI analysis results show that:
there is a generally good agreement between numerical results and recorded data both in time and in frequency domain
SASSI 2000 seems to be reliable to perform SSI analyses on the selected building when subjected to low-to medium intensity seismic events
The analysis results could be reasonably extended to other Italian sites with similar properties (two-storey concrete buildings lying on soft soils with deep bedrock in low-to-medium seismicity area)
the presence of the structure has a slightly damping effect
SSI does not seem to have a significant role in the selected site
