Time-dependent vulnerability assessment of RC buildings considering SSI and aging effects

Laboratory of Soil Mechanics, Foundations and Geotechnical Earthquake Engineering, AUTH

Time-dependent vulnerability assessment of RC buildings considering SSI and aging effects

Time-dependent vulnerability assessment of RC buildings considering

SSI and aging effects

Aristotle University of ThessalonikiDepartment of Civil Engineering

Laboratory of Soil Mechanics, Foundations & Geotechnical Earthquake EngineeringResearch Unit of Geotechnical Earthquake Engineering and Soil Dynamics

COMPDYN 2013, Kos Island, Greece June 2013

Sotiria Karapetrou

Argyro Filippa

Stavroula Fotopoulou

Kyriazis Pitilakis



Methodological framework

Selection of reference structures• Low and

medium rise RC frame buildings

• Modern seismic code design

Simulation of the structural models under study• Fiber based

approach• SSI• Corrosion

probabilistic models

Non-linear dynamic analysis

• 8 different outcropping real records

• Response parameter: maxISD(%)

Time-dependent fragility curves• IM: PGA• LS in terms

of maxISD(%)

• Incorporation of uncertainties


Time-dependent vulnerability assessment of RC buildings considering SSI and aging effects 3

Structural models

2-storey, 1-bay RC MRF building

Designed based on Greek modern seismic code

Material properties: Concrete C20/25 Steel B500C

Fundamental period: T1=0.3936sec

Gelagoti (2010)

Low-rise structural model



Structural models

4-storey, 3-bay RC MRF building

Designed based on

modern seismic code of Portugal

Material properties: Concrete fc=28MPa Steel fy=460MPa

Fundamental period: T2=0.5018sec

Abo El Ezz (2008)

4Φ18

+4Φ16 3Φ16+5Φ12+2Φ10

3Φ16+5Φ12+2Φ10

3Φ12+6Φ10

3Φ12+6Φ10

Mid-rise structural model



Finite element code OpenSees Material inelasticity Distributed material plasticity (fiber based approach)

Unconfined concrete:

Kent and Park model (1971)

Confined concrete:

Modified Kent and Park model

(Scott et al 1982)

Steel:

uniaxial bilinear steel material

object with kinematic hardening

Numerical modeling



Schematic view of the applied approaches



Soil-structure interaction (SSI) modelingSSI two-step analysis (Fotopoulou et al. 2012) 1st step: 1D equivalent linear analysis of the soil column 2nd step: Impedance function by Mylonakis et al. (2006)

CyberQuakeG-γ-D by Darendeli (2001)

Vs,30=300m/sec

→ free field surface motion

→ effective shear strain of the surface layer γeff



Soil-structure interaction (SSI) modelingSSI two-step analysis (Fotopoulou et al. 2012) 1st step: 1D equivalent linear analysis of the soil column 2nd step: Impedance function by Mylonakis et al. (2006)



Calibration of the soil parameters in terms of G = f(γ) και D(%) = f(γ) based on1D equivalent linear analysis conducted in Cyberquake for the SSI two-step analysis

Lysmer-Kuhlemeyer (1969) dashpot

Input Motion

Rigid beam-column element

30.0

m

Soil-structure interaction (SSI) modeling

Elastic Bedrock Vs=1000m/sec

120.0m

30.0

m

OpenSees

SSI one-step analysis

Free field

Soil profile 120m x 30m, 3600 four node quadrilateral elements Soil quad element 1m x 1m

Elastic soil layers Vs,30=300m/sec

Common nodes-Apropriate constraints



30.0

m

Soil-structure interaction (SSI) modeling

Soil profile 120m x 30m, 3600 four node quadrilateral elements

Soil quad element 1m x 1m

SSI one-step analysis

Lysmer-Kuhlemeyer dashpot at the base

Elastic soil layers

Calibration of the soil parameters in terms of G = f(γ) και D(%) = f(γ) based on1D equivalent linear analysis conducted in Cyberquake for the SSI two-step analysis

Elastic bedrock Vs=1000m/sec

Soil – structure: common nodes, appropriate constraints



Main parameters: W/C, Ccrit, Tini, icorr, Di, n

Probabilistic modeling of corrosion initiation time due to chloride ingress according to FIB-CEB Task Group 5.6 (2006)

Time-dependent loss of cross sectional area of reinforced bars based on Gosh και Padgett (2010)

Corrosion modelingCorrosion scenario for the t=50 years

Distribution of Chloride corrosion initiation time Tini

mean = 2.96 years Standard Deviation = 2.16 years

2i init

2

init

n D if t T4

A( t )max n D t ,0 if t T

4

i init

i corr init init

D if t TD( t )

max[ D i ( t T ),0 ] if t T



Nonlinear Dynamic Analysis 2D nonlinear time-history analysis for t=0 and 50 years

8 outcropping records corresponding to sites classified as rock or stiff soil according to EC8

3 scaling levels in terms of PGA: 0.1g 0.3g 0.5g



Ghobarah (2004) : max ISD(%) for ductile and non-ductile MRF systems

Scenario t=0 years: damage states for MRF – ductile structures Scenario t=50 years: damage states for MRF – non-ductile structures

Damage states Ductile MRF Non-ductile MRF

Light damage 0.4 0.2

Moderate damage 1.0 0.5

Severe damage 1.8 0.8

Collapse > 3.0 > 1.0

Definition of Damage States



ttmPGAPGADSP

lnln/

t : reference time

Lognormal distribution

Time-dependent fragility curves

m(t), β(t): PGA median values and logarithmic standard deviations at different points in time t along the service life (t=0 and 50 years)



Uncertainties

222dsCD

βD: demand (variability in the numerical results)

βC: capacity (HAZUS)

βds: definition of damage state (HAZUS)

Time-dependent fragility curves



0 0 .2 0 .4 0 .6

0

1

2

3

4

5

da taS lig h t d am ag eM o d e ra te d am ag eE x ten siv e d am ag eC o m p le te d am ag eP o w e r f it

y = 5 .9 7 5 3 x 0 .9 4 9 9R 2 = 0 .7 9 1 8

L o w r ise - flex ib le b a se - V s= 3 0 0 m /sec , t= 5 0 y ea rs

P G A (g )

ISD

max

(%)

0 0 .2 0 .4 0 .6

0

1

2

3

4

d a taS lig h t d am ag eM o d e ra te d am ag eE x ten s iv e d am ag eC o m p le te d am ag eP o w er f it

y = 4 .4 3 6 5 x 0 .9 9 7 6R 2 = 0 .8 0 1 6

L o w r ise - fix ed b a se - ro ck , t= 5 0 y ea rs

P G A (g )

ISD

max

(%)

0 0 .2 0 .4 0 .6

0

1

2

3

4d a taS lig h t d am ag eM o d era te d am ag eE x ten s iv e d am ag eC o m p le te d am ag eP o w er f it

y = 3 .5 2 8 8 x 1 .0 2 4 3R 2 = 0 .8 6 5 6

L o w r ise - fix ed b a se - ro ck , t= 0 yea rs

P G A (g )

ISD

max

(%)

0 0 .2 0 .4 0 .6

0

1

2

3

4

5d a taS lig h t d am ag eM o d e ra te d am ag eE x ten siv e d am ag eC o m p le te d am ag eP o w e r f it

y = 4 .7 7 8 3 x 0 .8 9 6 9R 2 = 0 .8 4 8 7

L o w r ise - flex ib le b a se - V s= 3 00 m /sec , t= 0 y ea rs

P G A (g )

ISD

max

(%)

Fragility curves PGA-ISDmax (%) for the low rise structures considering fixed and

compliant condition for t=0 and 50 years



Comparison with literature

Low rise strucural model designed

based on modern seismic codes

(t=0 έτη)

Fragility curves



Comparison with literature

Mid rise strucural model designed

based on modern seismic codes

(t=0 έτη)

Fragility curves



Fragility curves Low rise structural model

Aging effects→ Increase in vulnerability



Fragility curves Mid rise structural model

Aging effects→ Increase in vulnerability



Fragility curves Fixed and compliant (Vs=300m/sec) foundation conditions for t=0years

SSI and foundation compliance → Increase in vulnerability



Fragility curves Fixed and compliant (Vs=300m/sec) foundation conditions for t=0years

SSI → Decrease in vulnerability



Fragility curves Substructure (two-step) and direct (one-step) methods for SSI modeling



Fragility curves Percentage increase in vulnerability due to soil compliance

1 2 3 4D am age s ta tes

0

2 0

4 0

6 0

8 0

1 0 0

Perc

ent i

ncre

ase

(%) o

f vul

nera

bilit

y

4 9 .3 49 .8 50 .1 50 .347 .540 .1

35 .230 .2

T w o -s te p ap p ro achO n e-s tep ap p ro ac h

D S D S D S D S

L o w -r ise stru ctu ra l m o d el


0

2 0

4 0

6 0

8 0

1 0 0

Perc

ent i

ncre

ase

(%) o

f vul

nera

bilit

y

3 236 .9

40 .1 42 .6

28 .8 27 .3 26 .6 25 .7

T w o -s te p ap p ro achO n e-s tep ap p ro ach

D S D S D S D S

M id -r ise stru ctu ra l m o d el



Fragility curves


0

1 0

2 0

3 0

4 0

Perc

ent d

ecre

ase

(%) o

f vul

nera

bilit

y

0 .68 0 .73 0 .78 0 .81

16 .1

9 .16

4 .94

1 .3

T w o -s te p ap p ro ac hO n e-s te p ap p ro ac h

D S D S D S D S

L o w -r ise s tru ctu ra l m o d el

1 2 3 4D a m ag e s ta tes

0

1 0

2 0

3 0

4 0

Perc

ent d

ecre

ase

(%) o

f vul

nera

bilit

y1 .7

3 .1 4 4 .83 .5 9

11 .8

17 .2

22 .3

T w o -s te p ap p ro achO n e -s tep ap p ro ac h

D S D S D S D S

M id -r ise stru ctu ra l m o d el

Percentage decrease in vulnerability due soil-structure interaction



Conclusions

aging effects :

affect the dynamic response and the seismic vulnerability of the

structures

corrosion of reinforcement :

is considered as a loss of cross sectional area of reinforced bars

leads to significant increase of structure vulnerability due to the

considered “worst case scenario”

soil deformability and soil compliance :

modify the structural response of the analyzed structures resulting to

higher vulnerability values.

depends on: the characteristics of the building, the input motion and

the soil properties.



Conclusions

soil-foundation-structure interaction (SFSI): leads to decrease in structural vulnerability

the uncoupled two-step approach (substructure method) leads to higher

vulnerability (overestimation due to uncertainties related, among others, to

the evaluation of the impedance function)

further research in:

definition of limit states for corroded structures based on adequate

analytical, experimental and empirical data

incorporation of the fully probabilistic models within the dynamic analysis

Time-dependent vulnerability assessment of RC buildings considering SSI and aging effects

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