RockingFounda-onsforBridges

BruceKu4erSashiKunnathLijunDeng

JacquelineAllmond

Acknowledgements•  PEER support for shallow founda-on research for several years (mostly for building founda-ons) (Hutchinson, Gajan, Stewart, Mar-n, Moore, manystudents)

•  CurrentsupportfromCaltrans(Desalvatore,McBride,Shantz,andKhojasteh,Mahan&contract59A0575).

•  Caltrans project (Mahin, Jeremic, Alameddine andWhi4en)

•  NEES@UCDavis,CGMstaff,J.Ugalde,T.AlgieofUniv.ofAuckland,NZ.

•  New project of rocking founda-ons for bridges)fundedbyPEERasofOctober1.

(a)fixed‐fixed(b)fixed‐hinged(c)fixed‐rocking;(d)hinged‐rocking

WorkforCaltrans:Idealizedfailuremechanisms

(b)

Seismicload

Plas-chinges Plas-chinges

(d)Plas-chinges

Columnisprotectedbyrockingisola-onincase(d)

(a)

(c)

CaltransSDC:“founda(oncomponentsshallbedesignedtoremainessen(allyelas(cwhenresis(ngtheplas(chingingmoments”.

Destroyedcolumnsfrom1995Kobeearthquake

Inspectable,controllablewithproperreinforcing,butcatastrophicresultsifduc-litycapacityisexceeded.

•  Thereisacri-cal(minimum)contactlength,Lc,requiredtosupportthever-calload,V.

•  Momentcapacity(fromequilibrium)is

•  Lc/L<<1fortypicalbridgefounda-ons.•  ∴Mo,ult isinsensi-vetoLc /L

Defini-onsandbasicconcepts

T CDavidMar

Baseshakingtests

Dynamicbase‐shakingandslowcyclicloadingtestsonthe9mradiusNEESgeotechnicalcentrifugeatUCDavis.

Slowcyclicloadingtests

Ugaldemovie–L/Lc~30to50

Moment‐rota9on‐se:lementbehaviorofrockingfounda9onfromslowcyclictests

L/Lc=2.2 L/Lc=3

L/Lc=3.8 L/Lc=12

BridgeSystemConcepts

Smallfoo-ng

Largefoo-ng

Bridgesystemtestconfigura-on

LJD02_15event:Gazli2.0

Columnmom

ent(kN

*m)

Columnmom

ent(kN

*m)

Foo-ngRota-on(%) ColumnRota-on(%)

Small‐foo-ngbridge

Large‐foo-ngbridge

Foo-

ngm

omen

t(kN

*m)

Foo-

ngm

omen

t(kN

*m)

Cri-calplotsofLJD02_15event:Gazli2.0Ro

ta-o

n(%

)

Se4lemen

t(cm

)

Rota-o

n(%

)

Se4lemen

t(cm

)

Small‐foo-ngbridge

Large‐foo-ngbridge

•  Systemswithsmallfoo-ngsmayperformbe4erthansystemswithlargefoo-ngs–  drip,duc-litydemandoncolumns

•  Rockingfounda-onsprovide–  Self‐centeringtendency– Non‐degrading,welldefinedmomentcapacity–  Isola-onmechanism–  Energydissipa-on

•  Difficultaspectoftheproblem:Howtoevaluatese4lement(oruplip)associatedwithrocking.–  But,magnitudeofse4lementsisnotunreasonable.

Learnedfromexperiments

DraDDesignProcedureforBridgeswithRockingFounda9ons

1. Determinedesigngroundmo-ons,sitecondi-ons,designspectra.

2. Determinesuperstructureinforma-on,geometry,deadloadsandliveloads,abutmentconstraints.

3. Es-matedistribu-onofdeadloadonfoo-ngs.4. Sizefoo-ngsbasedonse4lementconsidera-ons.L/Lc>~10and“yieldaccelera-on”largeenoughtolimitdriptoacceptablelevels.

5. Preliminarycolumndesign:sizedtomaketheirmomentcapacitygreaterthanthefoo-ngmomentcapacity.

DraDDesignProcedureforBridgeswithRockingFounda9ons

6.Confirmthatdripandse4lementdonotviolateserviceabilitylimitsinFunc-onalEvalua-onEarthquake.Ifdripistoolargeincrease“yieldaccelera-on”

7.NocollapseinMaximumConsideredEarthquake.

8.Checkdistribu-onofdeadloadonthefoo-ngs(assump-oninstep3).

9.Finaldesignofcolumns

Hurdlestoimplementa9onofRockingFounda9onsforBridges

•  Overcomeexcessivefearof-poverofrockingsystems– Ahingeisahingeisahinge(MarkMoore)

•  Misconcep-onthatmomentcapacityof“soil”ishighlyuncertain

Hurdlestoimplementa9onofRockingFounda9onsforBridges

•  Se4lementassessment

SmallFSvLargeFSv

Se4lemen

tpercycle,s/L

Uplip,‐s/L

HalfAmplitudeofRota-on(radians)

Hurdlestoimplementa9onofRockingFounda9onsforBridges

•  Developdrapdesignprocedure– WorkwithCaltransengineerstoaddressconcernsandmakeitworkableandunderstandable

•  Reviseseismicdesignguidelines

•  Determinelimitsofapplicability(liquefac-on,watertable,sopground)– groundimprovement– mayextendlimits

•  ThanksagaintoPEER,Caltrans,andNSF