Current Issues in Evaluation of Seismic Site Effects

1Hashash (2014) – GI-Chicago - GLCC

University of Illinois at Urbana-ChampaignDepartment of Civil and Environmental Engineering

Current Issues in Evaluation of Seismic Site Effects

Youssef M.A. Hashash, Ph.D., P.E., F. ASCEIn collaboration with Byungmin Kim, Ph.D.

The 18th Great Lakes Geotechnical and GeoenvironmentalConference (GLGGC), &

The 2014 Chicago Geotechnical Lecture SeriesGeotechnical Earthquake Engineering

May 02, 2014; 1:00 pm- 2:00 [email protected]


Outline

• Introduction• Historical Evidence of Site Effects• Site Factors in Seismic Codes• Performance-based design• Site Investigation• Conditional Mean Spectra• Geologic and Tectonic Settings in the Eastern U.S.• Site Response issues in Eastern US• Concluding Remarks


Overview - Field EvidenceSan Francisco Earthquake, 1957

Flow failure Lake Merced USGS, 1957


Mexico City, Michoacán Earthquake, 1985

Building collapse NISEE, 1985

Overview - Field Evidence


Bay Bridge partial collapse NISEE, 1989

Loma Prieta, 1989Overview - Field Evidence


Northridge, 1994

Building collapse GEES, 1994

Collapse of sections of Interstate 5Arnesen Photography, 1994

0 50km

Id Station USGS Class1 Lake Hughes #12A A2 Castaic B3 Vasquez B4 Newhall - County Fire Sta. C5 Simi Valley - Katherine Rd & Sylvan C6 Arleta - Nordhoff Ave Fire Sta B7 Los Angeles - Hollywood Storage Gr. C8 Century City - LACC North B9 Pacific Palisades - Sunset & Carey B

10 Malibu - Point Dume B11 Downey - Imperial & Bellflower C12 Inglewood - Union Oil Yard B



Kobe, Hyogoken-Nanbu Earthquake, 1995. Vertical Array

Soils & Foundations (1996)



Seismic Code Site FactorsInfluence of local geology on ground motion generated by the Loma-Prieta EQ (Borcherdts and Glassmoyer 1992)• Locations of stations • Ground velocity


Seismic Code Site FactorsInfluence of local geology on ground motion generated by the Loma-Prieta EQ (Borcherdts and Glassmoyer 1992)

• Average spectral ratios inferred from Loma-Prieta strong motion data

• For different period bands

These measurements provide an empirical basis for amplification factors for construction of response spectra.


Seismic Code Site Factors

(Borcherdt 1994)

• Site-dependent response spectra using site factors



Borcherdt 1994

Sit classes based on borehole logs for the San Francisco and LA regions



(Borcherdt 1994)• Site factors with respect to Vs = 1050 m/s



Borcherdt 1994

Site factors with respect to Vs = 1050 m/s


ASCE Site Factors

2010 ASCE-7 Section 11

Site factors are applied to Site Class B/C.

VS ~ 1524 m/s 762 366 183

See also Seyhan & Stewart 2012


GOING BEYOND GENERIC SITE FACTORS


Seismic Code vs. Site-specific analysis

• Simplified procedure (Site factors Fa & Fv, Site classes)- Widely used but…

• Site-specific analysis is needed for- Eastern US: Hard Rock (different reference rock

conditions, high frequency content)- Shallow reference Rock (<30m)- Non-NEHRP site conditions

- Thick sections (> 30 m) of F, E, and E/D soils- Thin sections (5-15m) of soil over hard rock

- Special and critical structures


Need for Site-specific study

• Site Classification: If the subsurface conditions classify a site as Site Class F, the codes require a site-specific study.

• Cost Optimization: If the owner wants to reduce construction costs, a site-specific study can performed to reduce dynamic loads and the Seismic Design Category (SDC).

• Analysis Method: If the importance of a structure or the variability of subsurface conditions require parameters that are not readily available in codes, such as soil structure interaction parameters or time histories of acceleration

(Nikolaou 2008)


Performance-based design

PerformanceSelect Preliminary

Objectives

Develop PreliminaryDesign

AssessPerformance

Capability

AssessPerformance

Capability

PerformanceDoes

MeetObjectives?

DoneDone

and/or

Performance Objectives

No

Revise Design

No

Owner

Designer

Building Official

YesYes

Building Official&

Peer Reviewers

After R. O. Hamburger

Peer Reviewers

PeerReviewers


Input needed - Site Investigations

• Vs – Shear wave velocity -direct measurement: e.g. P-S suspension logging

• sCPT: seimic cone penetrometer

• Thorough geohazardevaluation

• Thorough site-specific seismic hazard evaluation, conditional mean spectra, ground motion selection


Beyond UHS –CMS for site-specific seismic analysis

• UHRS envelops possible spectra large seismic demands.• Deterministic Spectra are not associated with return period.• CMS bridges UHRS and Deterministic Spectra.

Latit

ude

(

(Hashash et al. 2013)


Frequency Domain (FD)Time Domain

Complexity of the problem:

1D2D3D

Site Response Analysis

Focus on 1-D site response analysis for practical engineering applications.


0.000

1.000

2.000

3.000

4.000

0 10 20 30 40 50Frequency(Hz)

TF0.000

0.005

0.010

0.015

0.020

0.025

0 10 20 30 40 50Frequency

Four

ier a

mpl

itude

0.000

0.005

0.010

0.015

0.020

0.025

0 10 20 30 40 50Frequency

Four

ier a

mpl

itude

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0 2 4 6 8 10Time(sec)

Acce

lera

tion(

g)

FFT

FFT-1

soil =

• Frequency Domain Methods / Equivalent-Linear (a.k.a SHAKE)

Site Response Analysis - EL

0.0

0.2

0.4

0.6

0.8

1.0

G/G

0

0.0001 0.001 0.01 0.1 1 10Shear Strain - - [%]

0

5

10

15

20

25

Dam

ping

-

- [%

]

Target CurveIteration 1Iteration 2Iteration 3

a)

b)

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0 2 4 6 8 10Time(sec)

Acce

lera

tion(

g)


Site Response analysis –EL• Robust procedure• Widely used• Extensively verified

• Variation in stiffness with strain amplitude?• Results under large strains or strong ground

motion? • Evaluation of pore water pressure generation?


Site Response Analysis - NL1D Wave Propagation – Time Domain Solution

guIMuKuCuM

[C]: Damping matrix → Viscous DampingRayleigh Damping

Exhibit frequency dependent behaviorSubject of a paper under development

[M]: Mass matrix → Less uncertaintyStraightforward calculation

[K]: Stiffness matrix → Nonlinearity: Recalculated in each time step

Use of simplified models (i.e. Hyperbolic Model or Ramberg

Osgood)Modulus ReductionHysteretic Damping

Equation of Motion:Numerical Solution:

1h11 ,G

Layer1

2

i

n

22 ,G

ii ,G

nn ,G

3 33 ,G

EE ,G

iii hm

22 21 mm

22 32 mm

21m

2nmSEEE VC nn c,k

11 c,k

22 c,k

33 c,k

2h

3h

nh

ih

Layer Properties

G: shear modulus: density

VS: shear wave velocityh: thickness

Equivalent Lumped Mass System

k: stiffnessc: viscous damping


Site Response Analysis - NL1D Wave Propagation – Time Domain Solution

Gsec1

Gsec2

Backbone Curve

Initial LoadingCurve

SubsequentLoading & Unloading Curves

guMuKuCuM

Dynamic Equation :

Modified Kondner-Zelasko(MKZ) model (Matasovic 1993)

s

r

G

1

0

revs

r

rev

revG

21

22 0

1

2

1

2

www.illinois.edu/~deepsoil


Site Factors for Mississippi Embayment

-93 -92 -91 -90 -89 -88Longitude ()

34

35

36

37

Latit

ude

()

1

23

45

6

78

9

Unit of contour: m

Uplands

Lowlands

Carbondale

Memphis

(Hashash and Moon 2011)

a) Develop a synthetic earthquake catalog based on 2008 USGS hazard map.b) Use GMPEs to calibrate SMSIM and EXSIM.c) Propagate ground motions through soil column using DEEPSOIL.d) Compute depth-dependent NHHRP style site amplification factors.


Site Factors for Mississippi Embayment

(Hashash and Moon 2011)• Site factors (Fa and Fv) with respect to PGA• Depth-dependent site factors


Site Amplification Factors• Boore et al. (1997)

Abrahamson and Silva(1997)

Choi and Stewart (2005)

Walling et al. (2008)

*VS30:time-averaged shear-wave velocity in the upper 30

meters of sediments.


Site Amplification Factors for NGA-West

Amplification of SA (T=0.2sec) (Walling et al. 2008 )


Seismic Hazard Map in the Eastern U.S.

(USGS 2008)

PGA for 2475-year return period PGA for 475-year return period

For Site Class B/C (~760 m/s)


Seismicity in New York


Bedrock in New York

(Moss 2010)

Shallow bedrock


Bedrock in the Eastern U.S.

Nikolaou et al. (2012)


Reference Rock in the Eastern U.S.

0 2000 4000 6000 8000Wave Velocity (m/s)

120

100

80

60

40

20

0

PS LoggingAvg. of PSLDownhole

Ref. Velocity (PSL)

Ref. Velocity (Downhole)

S-wave P-wave

0 2000 4000 6000 8000Wave Velocity (m/s)

S-wave

P-wave

(a) (b)

• Vs and Vp measurements that penetrate hard-rock were collected- Journal publications and technical reports- Nuclear power plant applications

• Locations of 283 profiles

Bell Bend NPP

(Hashash et al. 2013)


Reference Rock in the Eastern U.S.S-

Wav

eV

eloc

ity,V

s(m

/s)

Bel

lBen

dN

PP-8

Bel

lefo

nte

NPP

-8B

rons

on-A

valo

n-1

Cal

law

ayN

PP-2

Cal

vert

Clif

fs-3

Cha

lkR

iver

,Ont

ario

-1C

linto

nN

PP-1

Com

anch

ePe

akN

PP-1

Ferm

iNPP

-2G

rand

Rem

ous,

Ont

ario

-1H

artfo

rd-1

Hay

es-1

Mon

ticel

loR

eser

voir

-3N

ine

Mile

NPP

-1N

orth

Ann

aN

PP-2

Otta

wa,

Ont

ario

-1PS

EGN

PP-1

Riv

erB

end

NPP

-1Sh

earo

nH

arris

NPP

-1Tu

rkey

Poin

tNPP

-1Ty

nesid

e,O

ntar

io-1

V.C

.Sum

mer

NPP

-8V

ogtle

NPP

-3W

ater

bury

-1W

esle

yvill

e,O

ntar

io-1

Will

iam

sbur

g,O

ntar

io-1

Will

iam

Stat

esLe

eIII

NPP

-12

Best Estimate RangeVs,ref 3.0 km/sec 2.7 ‐ 3.3 km/secVp,ref 5.5 km/sec 5.0 ‐ 6.1 km/sec (Hashash et al. 2013)


Seismic Codes in the Eastern U.S.



Seismic Codes in the Eastern U.S.


• Site factors from seismic code are smaller than equivalent site factors derived from site-specific site response analysis


Site-specific Seismic StudySite Class C/D in Yonkers, NY (Nikolaou and Go 2009)

• The site condition was reclassified using measured in-situ Vs.


Site-specific Seismic StudySite Class E in Brooklyn, NY (Nikolaou and Go 2009)

• Estimated Vs from SPT N-values, and performed a 1-D site response analysis

• Site-specific response spectrum is lower compared to the code’s Site Class E spectrum. reduction of design acceleration by 20%


Site-specific Seismic StudySite Class C/D in Brooklyn, NY (Nikolaou and Go 2009)

• Performed in-situ field testing and site response analyses.• Reduction of acceleration from the Class D values.


Concluding Remarks

• Need to update current code factors

• Code based design vs. site-specific analysis (Performance-based design)

• Site Investigation & input ground motions

• Site and region specific evaluations differ from code site factors


Thank You

Questions


Relevant references:

• Hashash, Y. M. A. and D. Park (2001). "Non-linear one-dimensional seismic ground motion propagation in the Mississippi embayment." Engineering Geology 62(1-3): 185-206.

• Hashash, Y. M. A., N. A. Abrahamson, S. M. Olson, S. Hague and B. Kim (in press). "Conditional mean spectra for seismic analysis of a major bridge crossing in the central U.S.“, Earthquake Spectra

• Borcherdt, R. D. (1994). "Estimates of site-dependent response spectra for design (Methodology and Justification)." Earthquake spectra 10: 617-653.

• Hashash, Y. M. A. and S. Moon (2011). Site amplification factors for deep deposits and their application in seismic hazard analysis for Central U.S. . USGS. USGS/NEHRP Grant: G09AP00123: 91 pages.

• Baker, J. W. and C. A. Cornell (2006). "Correlation of response spectral values for multicomponent ground motions." Bulletin of the Seismological Society of America 96(1): 215-227.

• Baker, J. W. (2011). "Conditional mean spectrum: Tool for ground-motion selection." Journal of Structural Engineering 137(3): 322-331.

• Nikolaou, S, J.E. Go, C.Z. Beyzaei, C. Moss, and P.W. Deming, Geo-Seismic design in the Eastern United States: State of Practice, Geotechnical Engineering State of the Art and Practice

• Nikolaou, S and Go, J. (2009). “Site-specific seismic studies for optimal structural design: Part II - Applications.” Structure Magazine

REFERENCES

Documents

Current Issues in Evaluation of Seismic Site Effects