competing against time

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COMPETING AGAINST TIME
Report to Governor George Deukmejian
from
The Governor's Board of Inquiry
on the 1989 Loma Prieta Earthquake
w:
George Housner, Chairman
May 1990
COMPETING AGAINST TIME
Report to
Governor George Deukmejian
from
The Governor's Board of Inquiry
on the 1989 Lorna Prieta Earthquake
George W. Housner, Chairman
Joseph Penzien, Vice Chairman
Mihran S. Agbabian
Christopher Arnold
Lemoine V. Dickinson,Jr.
Eric Elsesser
I. M. Idriss
Paul C.Jennings
''''alter Podolny,Jr.
Alexander C. Scorde1is
Robert E. Wallace
Charles C. ThielJr., Editor
May 31,1990
Copyright©1990bythe StateofCalifornia, OfficeofPlanningand Research.
Excerpts from this report,exceptmaterialscopyrighted byothers, maybe
reproduced for non-commercial usc with attribution tothe California Gover
nor'sBoard ofInquiryon the 1989 Lorna Prieta Earthquake.
Additional copies ofthisreportand infonnation on current prices may be
obtained bycontactingthe OfficeofPlanningand Research Infornlation Center
at(916) 312-6312 or:
DepartmentofGeneral Services
Publications Section
P. O. Box 1015
North Highlands, California95660
[phone]
"
Acknowledgements
The Board ofIn<luiryappreciates theopportunitygiven to them byGovernorGeorge
Deukmejian toexamine the engineeringimplicationsofthe Loma Prieta earthquake. He provided
the cnvironmem in which our recommendationswere developed solelyon the basisoftheirmerit.
The Board would like toexpress itsappreciation toall those whodirecdyand indirectlysup
ported itseffortS. It received the full cooper-aion and supportofall the individuals and institutions
that appeared before ir. Individualsandorganizations from St:ucand local government. universities,
professional associations, and the public unselfishly<:ontributcd theirtime and expertise ro the
deliberations ofthe Board. vVithoutexception, those who appeared before the Board gave thought
ful and knowledgeable testimony. Officialsandstafffrom all State, local, :lnd independentagencies
appearingbefore the Board were verycoopcrativc, including: DcpartmentofTransporration; De
partmcntofConservation, Division ofMinesand Gcology; Highway Patrol; San Francisco Bay
Conservation and De\"elopmentCommission; State Board ofRcgistration for Professional Engi
ncers; Deparnncntof"Vater Resources, Division ofDam Safety; DepartmentofFinance; Seismic
SafctyCommission; Golden Gate Bridge District; BayArea RapidTransit District; and, the Cityof
LosAngeles. Caltransprovided forthright testimonyand expended considerableeffort in providing
information and data requested by the Board; the helpful cooper:ltion ofj.R. Roberts andj.J-1. Gates
is acknowledged.
The effortsofmanyindividuals contributed tothe Board's work. Dr.John F. Hall, whoserved
asTechnical Secretaryto the Board,and Mr. Ben \,villiams,whoserved asAdministrati\'e Officer,
made importantcontributions tothe completion ofthe report. Dr. Pat ReddyprO\~dedtechnical
support rothe Chainnan and Mr. PetcrMilne assistcd the Board with meetingarrangements. The
srudiesand testimonybythe research teams from the UnivcrsityofCalifornia at Bcrkeley were
particularly important tothe Board's understandingofthe C}1)reSS Viaductand Bay Bridge failures:
S. A. Mahin,j.P. Moehle, A. Astaneh, D.K. Nims, E. Miranda, J.D. Aiken, A.S. \Vhinaker, and
V.V. Bertero, investigarors. Prof. Abolhassall Astaneh provided valuable insighton the performallce
ofthe Bay Bridge and Dr. Andrew S. \Vhitraker was particularly helpful in understandingwhat
happened to the San Francisco Freeway Viaducts.
The editingofthis report wasdone byGail H. Shea, graphicdesign wasdone by Laura H.
,\·toger, and line artwasproduced by PrintzofSan Francisco. The Board appreciates theirefficient
cooperation.
Finally, Dr. Charles C. ThielJr. undertook the technical task oforganizing and editing the
contributionsofBoard members intoacoherent form, and alsocontributed portionsofthe text. His
efforts are gre:ltlyappreciated.
George \·V. Housner
Chainnan
'"
This page has been left intentionally blank.
Table of Contents
Acknowledgements .
'"
Table ofContents . v
Preface .
VII
Chapter I Overview . I
The Governor's Directives the BoardofInquiry . 2
[Q
'rhrec Challenges .. 9
Recolllillendatiolls . 9
Chapter 2 Governor's Board of Inquiry .. 1l
Membershipofthc BoardofInquiry . 1l
Meetings Held andTestimony Rccci\·ed .. 17
Other Information Considered bythe BoardofInquiry . 17
Chapter 3 The Eanhquake's Impact on Transportation Systems . 19
'rhe Earthquake .. 19
OvcrviewofDalllage to Bridges .. 2J
ImpaclSon Cross-BayTransportation . J4
Ilnportanccofthc Bay Crossinb"S . 36
Conclusions . 39
Chapter 4 Findings . 43
Findinb"Son ScisTllo[Ob'Yand Ground l'vlotion . 44
GCllcral Findinb"Son Transportation Structurcs . 47
Findinb"Son Caltrans Seismic Design Practices . 51
Findinb"Son thc Bay BridgeSpan Failurc . 36
Findinb"Son C}'llrCSS Viaduct Collapse . 59
Findinb"Son San Francisco FrcewayViaducts .. 63
Findinb"Son Retrofit Program . 65
Findings for OthcrT}rpcsofStrucrures .. 69
Chapter 5 Recommendations to Improve California's Earthquake Safety .. 75
Rcconllllcndations for the Govcrnor . 76
RccoTlllllcndations for thc Dircctorofthc DcparnncntofTranspor~rion . 80
Recomlllendations for Transportation Agenciesand Districts . 86
Chapter 6 Seismology and Ground Motion . 89
Char;lctcristicsofRccorded Ground Motions . 93
Selectcd StrongMotion Rccords . 97
Spectral Ordinales . 101
Potcntial for Damaging Earthquakcs in thc San Francisco BayArca .. 107
Conclusions . 114
,.
Chapter 7 Seismic Design Codes in California . 117
Research on Reinforced Concrete BridgeStructures . 117
Uniform BuildingCode (UBC) 120
Caltrans Seismic Design Criteria, 1940-1971 122
Caltrans Post-197l Seismic Requirements 123
AASI-rro Seismic Design Codes for Bridges 125
ComparisonsAmong Codes : 126
Conclusions 128
Chapter 8 The California Bridge Seismic Retrofit Program .' 129
Earty History 129
Recent Events 133
Conclusions 135
Chapter 9 San Francisco-Oakland Bay Bridge 137
Hisroryofthe Bay Bridge 137
Alignment, Structural Configuration, and Foundation Conditions 139
Seismic Retrofitofthe East BayCrossing 143
Damage Caused by the Loma Prieta Earthquake 144
RepairofDanlage 149
AssessmentofSeismic Loads Experienced During the Earthquake 150
Conclusions 153
Chapter 10 The Cypress Viaduct Collapse 155
I-listoryofCypress Viaduct 155
Design ofthe CypressViaduct 156
Description ofCypress ViaductStruCture 158
Seismic RetrofitofCypress Viaduct in 1977 166
Earthquake Damage and FailureModes Sustained by the Cypress Viaduct 167
Typical Bent FailureJV10de 174
Nontypical Bent Failure Mode 176
Standing Bents in the Cypress Viaduct 176
Results ofAnalytical Investigations 177
Experimental Investigations 182
Conclusions 188
Chapter 11 San Francisco Freeway Viaducts 191
Description ofthe Six San Francisco Freeway Viaducts 193
Lateral Load Resisting Systems 197
Earthquake Damage Sustained by the San Francisco Freeway Viaducts 204
Conclusions 215
Chapter12 Repair and Upgrade ofthe San Francisco Freeway Viaducts 217
Caltrans Seismic Upgrade Criteria 217
Seismic Upgrade Experimental Data . 220
Seismic UpgradeAnalysisand Design Methodology 221
General Discussion ofthe UpgradingApproaches 222
Specific UpgradingApproaches 224
Conclusions 226
Appendix 229
Annotated Bibliography 235
v,
Preface
Cm'cmaTGeorge Deukmejiall ap Thesechallengesarc addressed
pointed an Independent Board ofInquiry to notonlyto thedesign and construc
reporton the October 17 •1989 Lollla tionofbridges.whose failure
Prieta earthquake. The fonll3tion ofthe prompted the Board's fonnation, but
Board was prompted byearthquakedamage also toall the otherconstructed
to bridges and freeway strucrurcs and the facilities upon which our modern
desire to know notonlywhat happened, but economyand well-beingdepend.
how to preventsuch destruction in future The Loma Prieta earthquake
earthquakes. The Governorcharged the should be considered adearand
Board with reportingon the causes of powerful warningto the peopleof
damageand what implicationsthese findings California. Although progresshas
haveon the California highwaysystem. been made during the past two
Future earthquakes in California are decades in reducingearthquake risks,
inevitable. Earthquakes largerthan Lorna much morecould have been done,
Prieta with morc intensegroundshaking and awaitsdoing. More aggressive
will occur in urban areas and have severe efforts to mitigate the consequences
consequences-too large tocontinue ofearthquakes are needed iftheir
"businessas m.ual." The vast majorityof disastrous potential is tobe mini·
struCtures that will fail in future earthquakes mired and one ofthe most funda·
exist now-bridges, buildings, industrial mental ofresponsibilitiesofgovern·
facilities,and utilities. The Board ofInquiry ment is tobe fulfilled-to provide for
has identified threeessential challengesthat the publicsafety.
must beaddressed bythecitizensofCalifor The State ofCalifornia must not
nia, iftheyexpect a future adequatelysafe waitfor the nextgreatearthquake,
from earthquakes: and the likelytensofbillionsof
• Ensure that earthquake risks posed by dollarsdamage and thousands of
newconstruction are acceptable. casualties, toaccelerate hazard
• Identifyand correct unacceptable mitigation measures. California must
seismicsafetyconditions in existing recognize that it has an earthquake
structures.
• Develop and implementactions that
foster the rapid, effective.and economic
response toand reco\'ery from damag
ingearthquakes
VB
problem thatcan be mitigated. Itis hoped The Board ofInquiryurgesthe public
that the Board's findings and recommenda and the State to take the actions necessary to
tionswill provideapositive impetustoward implement itS recommendations. Eanh
actions thatwill provide adequate earthquake quakeswill occur-whcthcr theyarc cataS
safety. trophesor not dependson ouractions.
tI"~J<r (;2:r(·~
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L
Gcor~c
/ \:\,!. Housncr, Chairman Joseph Penzien, Vice Chairman
(),Mh;toi/ rei
t1
rn
Mihran S. Agbabian £ChristophLerArnold
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L ..
Dickinson,Jr~
Lcmoinc V. Eric Elsesser
"';&. p.-
''7 . 'l"4d2, •• / (/<-1 c?
I. M. Idriss Paul C.Jennings
AlexanderC. Scordclis
Raben E. Wallace
Vlll
Chapter 1
Overview
Furure earthquakes in California arc in expressed asdirectdamage, indirect lossof
evitable. Tney represent aclearandcontinu utilities, increascd taxation, or reduced
ingdangertoourpopulation and economy. economicactivity. RecentS<.;entific research
The consequencesofsevereearthquakes in tells usthat there isahigh probabilityofa
urban areaswill be extensive-too large for majorearthquake in both southern and
"businessas usual.n It is time for California northern California within the next few
tosetpriorities for seismicsafety. Research decades. The Lama Priem earthquakeof
and development mustbe supported [0meet October 17, 1989,aMagnitude 7.1 earth·
ourneeds for effective, economicstrarcbries quake thatoccurred in asparselysettled
for earthquake hazards mitig':"ltion. \¥c must portion ofthe Sanrn Cruz mountains, caused
act forcefully to reducc the risks, vulnerabil damage approaching$6 billion and the
ity, and exposure we all share. collapse ofbuildingsand StruCtures as far
While the principal responsibility for awayas 60 miles in San Francisco and
California'scanh(IUakcsafety lies in the Oakland.
hands ofindividuals, governmenthas :In The Loma Priet:1 earthquake was but
important role. The mostfundament,11 one in aseriesofrecentd:llnagingearth·
responsibilityofgovernmentis to provide for quakes; otherssince 1970include \Nhittier
the publicsafery. Governor George Narrows, San Fernando, Coalinb"3, l\1organ
Deukmcjian appointcd thc Hoard ofInquiry Hill, Ferndale, Imperial County, Palm
on the Loma Pricta e:lrthquakeofOctober Sprinb'S, Livermorc Valley, l\'lammoth Lakes,
17, 1989 to dctcrmine thecauseofcollapses Santa Barbar;l, and Orovillc. Each ofthcse
ofthe Cypress Viaduct and Bay Bridgc span event.'ihascaused Structures to fail. In many
and to recommend actionsbased on this cases those that failed could have becn
experience that will limit thc impactsof identified as beingat high risk in an carth
future earthquakes. Thisdocument isthe quake. Each ofthese eventswasserious and
response ofthe BoardofIJHluiryto the calamitous tothose affectcd, evcn though
Governor'scharge. each was relativelyminorcompared to thc
Thevast majorityofstructures that will earthquakes thatarccxpected tooccur ncar
fail in future earthquakesexist now-bridges, mctrolXllitan areasalongthe northern and
buildings, industrial facilities, and utilities. southern San Andreas, Hayward, or New
The citizensofCalifornia arc captivesof port-lnglewood faults, toname but:l few
these existing ha7..ards/lnJrss newapproaches acti\'e faults within the State.
for mitigating thcm arcdcveloped and In 1980 the National Security Council
applied, measures thatdesign professions, estimated that asingle California earthquake
businesses, individuals, andgO\'ernment hasthe potential tocausc from 20 to80
officialscan economically usc. billion dollars in damage and kill tensof
E\'cl')'Californian isaffected by the thousands. In termsoftoday'svalues, tornl
occurrcncc ofa majorearthquake, whether damage impacts would be at least twiceas
Overview 1