An Evaluation of Current Site Response Analysis Methods

Chandrakanth Bolisetti Graduate Student Researcher

Dr. Andrew Whittaker Professor and Chair

Department of Civil, Structural and Environmental Engineering

University at Buffalo, SUNY

The City Block Project

Acknowledgments

• National Science Foundation, CMMI 0830331

• Dr. Amjad Aref, University at Buffalo

• Ibrahim Almufti and Dr. Michael Willford, ARUP San Francisco

• Dr. Boris Jeremic, UC Davis

• Dr. Ben Mason, Oregon State University

Overview

• Soil-structure interaction analysis for performance assessment of buildings and nuclear power plants

– Detailed 3D analyses

– Nonlinear analyses for high intensity ground motions

• Evaluation of existing industry-standard numerical tools

– Site response analysis (pre-requisite for SSI analysis)

– SSI analysis

• SSSI analysis

Overview

• Soil-structure interaction analysis for performance assessment of buildings and nuclear power plants

– Detailed 3D analyses

– Nonlinear analyses for high intensity ground motions

• Evaluation of existing industry-standard numerical tools

– Site response analysis (pre-requisite for SSI analysis)

– SSI analysis

• SSSI analysis

Outline

• Introduction

• Numerical Tools

• Numerical Analysis

• Sample Results

• Conclusions and future research

• Purposes

– Site effects for seismic hazard analysis

– Soil-structure interaction analysis

Introduction Site Response Analysis

1D site response analysis

• State-of-the-art

– Frequency domain equivalent linear analysis • SHAKE, DEEPSOIL

– Time domain nonlinear analysis • DEEPSOIL nonlinear, LS-DYNA

– Mostly 1D

• Limitations – Mostly developed for characterizing site effects

– The 1D assumption

• Horizontal ground motion components are usually not uncorrelated

• Not sufficient for high fidelity SSI analyses required for performance assessment of NPPs (Jeremic, 2011)

Introduction Site Response Analysis

Numerical Tools Frequency Domain

• The equivalent linear approach: SHAKE and DEEPSOIL – Seed and Idriss (1969)

– Iterative procedure

– Modulus reduction and damping curves

• Effective shear strain ratio

– An empirical value of 0.65 is recommended

Hashash et al, 2010

1

10

MR

Numerical Tools Time Domain

• DEEPSOIL nonlinear – MKZ model (Matasovic, 1993)

– Extended Masing rules define the stress-strain hysteresis

– Outcrop input using the Joyner and Chen (1975) method

0

1

s

r

G

Hashash and Park (2001)

Numerical Tools Time Domain

• LS DYNA nonlinear – General finite element analysis

– Column of solid elements constrained to move in shear

– MAT_HYSTERETIC model (MAT_079)

– Outcrop input using the Joyner and Chen (1975) approach

– ARUP, San Francisco

Numerical Analyses Site Selection

Site E1 Site E2 Site W1 Site W2

2500m/s

300m/s

2500m/s

1000m/s 300m/s

Bed Rock 2500m/s

Bed Rock 2500m/s

Bed Rock 1000m/s

Bed Rock 1000m/s

100m

Numerical Analyses WUS Ordinary motions

0.01 0.1 1 100

0.2

0.4

0.6

0.8

GM-1

GM-2

GM-3

Site-W1

Site-W2

WUS ordinary ground motions

Period (sec)

Acc

eler

atio

n (

g)

Event Station PGA (g)

Northridge, 1994 Vasquez Rocks Park 0.15

Northridge, 1994 Wonderland Ave 0.17

San Fernando, 1971 Lake Hughes #4 0.19

Numerical Analyses WUS Pulse motions

Event Station PGA (g) Tp (sec)

Landers, 1992 Lucerne 0.73 5.1

Northridge, 1994 Rinaldi Receiving Stn. 0.83 1.5

Chi Chi, Taiwan, 1999 TCU 128 0.19 9.0

0.01 0.1 1 100

1

2

3

LCN260 Tp = 5.12 sec

RRS228 Tp = 1.51 sec

TCU128 Tp = 9.00 sec

Site-W1

Site-W2

Acceleration response spectra for selected pulse motions

Period (sec)

Acc

eler

atio

n (

g)

Numerical Analyses CEUS motions

Event Station PGA (g)

Virginia, 2011 Charlottesville 0.10

New Hampshire, 1982 Franklin Falls Dam 0.31

Saguenay, CA, 1988 Dickey 0.09

0.01 0.1 1 100

0.25

0.5

0.75

1

CVA090

FFD315

SNY090

Site-E1

Site-E2

CEUS ordinary ground motions

Period (sec)

Acc

eler

atio

n (

g)

Sample Results Site E1, Charlottsville

0.01 0.1 1 100

0.1

0.2

0.3

0.4

Shake

Mat Hysteretic

Deepsoil

Comparison of acceleration response spectra at the surface

Period (sec)

Acc

eler

atio

n (

g)

0 0.025 0.05 0.075 0.1100

75

50

25

0

Shake

Mat Hysteretic

Deep soil

Peak acceleration profiles

Peak acceleration (g)

Dep

th b

elow

surf

ace

(m)

0 1 104

2 104

3 104

4 104

100

75

50

25

0

Shake

Mat Hysteretic

Ramberg Osgood

Deepsoil

Peak strain profiles

Peak strain (%)

Dep

th b

elow

surf

ace

(m)

Sample Results Site W1, Vasquez Park

0.01 0.1 1 100

0.2

0.4

0.6

0.8

Shake

Mat Hysteretic

Deepsoil

Comparison of acceleration response spectra at the surface

Period (sec)

Acc

eler

atio

n (

g)

0 0.05 0.1 0.15 0.2100

75

50

25

0

Shake

Mat Hysteretic

Deepsoil

Peak acceleration profiles

Peak acceleration (g)

Dep

th b

elo

w s

urf

ace

(m)

0 0.01 0.02 0.03 0.04100

75

50

25

0

Shake

Mat Hysteretic

Deepsoil

Peak strain profiles

Peak strain (%)

Dep

th b

elo

w s

urf

ace

(m)

Sample Results Site W1, Rinaldi

0.01 0.1 1 100

0.5

1

1.5

2

Shake

Mat Hysteretic

Deepsoil

Comparison of acceleration response spectra at the surface

Period (sec)

Acc

eler

atio

n (

g)

0 0.375 0.75 1.125 1.5100

75

50

25

0

Shake

Mat Hysteretic

Deepsoil

Peak acceleration profiles

Peak acceleration (g)

Dep

th b

elo

w s

urf

ace

(m)

0 0.5 1 1.5100

75

50

25

0

Shake

Mat Hysteretic

Deepsoil

Peak strain profiles

Peak strain (%)

Dep

th b

elo

w s

urf

ace

(m)

Conclusions

• Good match for low soil strains but large differences at high soil strains (close to 1%)

• Peak strain values are underestimated in SHAKE, especially for intense motions – Effective shear strain ratio?

• Accelerations are underestimated in SHAKE – Large values of damping ratio?

• Implications for SSI analysis – Need to be cautious when large strains are expected

– 1D analysis insufficient (Jeremic, 2011)

– Materials not suitable for full SSI analyses

Conclusions

• High frequency ‘noise’ in time-domain analysis results – Piecewise nonlinearity (LS DYNA only)

– Internal wave reflections due to impedance changes

– Joyner and Chen (1974)

– Cautious site layering, or filtering of the response

• SHAKE response for pulse motions – Convergence issues

– Smaller value of effective shear strain ratio needs to be used

Contacts

Chandu Bolisetti: cb76@buffalo.edu Dr. Andrew Whittaker: awhittak@buffalo.edu