CE2403 - Basics of Dynamics and Aseismic Design

UNITI
PARTA
1.

WhatismeanbyFrequency?

Frequencyisnumberoftimesthemotionrepeatedinthesamesenseoralternatively.
Itisthenumberofcyclesmadeinonesecond(cps).ItisalsoexpressedasHertz(Hz)
namedaftertheinventoroftheterm.Thecircularfrequencyinunitsofsec1isgivenby2f.
2.

Whatistheformulaforfreevibrationresponse?

Thecorrespondingequationunderfreevibrationscanbeobtainedby
substitutingtherighthandsideofequationaszero.Thisgives
mu+Cu+Ku=0
3.

Whataretheeffectsofvibration?

i.

EffectonHumanSensitivity.

ii.

EffectonStructuralDamage

4.
Whatismeanbytheoryofvibration?
Vibrationisthemotionofaparticleorabodyorasystemofconcentratedbodieshavingbeen
displacedformapositionofequilibrium,appearingasanoscillation.
Vibrationwasrecognizedinmechanicalsystemsfirstandhencethestudyof
vibrationsfellintotheheadingMechanicalVibrationsasearlyabout4700ago.
5.Deinedamping.
1.Damping is a measure ofenergydissipation in a vibrating system. The dissipating
mechanismmaybeofthefrictionalformorviscousform.Intheformercase,itiscalleddry
frictionorcolumndampingandinthelattercaseitiscalledviscousdamping.
2.Dampinginastructuralsystemgenerallyassumedtobeofviscoustypeformathematical
convenience.Viscousdampedforce(Fd)isproportionaltothevelocity
(u)ofavibratingbody.Theconstantofproportionalityiscalledthedampingconstant(C).
ItsunitsareNS/m.
6.

WhatdoyoumeanbyDynamicResponse?

TheDynamicmaybedefinedsimplyastimevarying.Dynamicloadistherefore
anyloadwhichvariesinitsmagnitude,directionorboth,withtime.Thestructural

response(i.e.,resultingdisplacementsandstresses)toadynamicloadisalsotimvaryingor
dynamicinnature.Henceitiscalleddynamicresponse.
7.

Whatismeanbyfreevibration?

Astructureissaidtobeundergoingfreevibrationsiftheexcitingforcethat
causedthevibrationisnolongerpresentandtheoscillatingstructureispurelyunder
influenceofitsowninertiaormass(m)andstiffness(k).Freevibrationcanbesetinby
givinganinitialdisplacementorbygivinganinitialvelocity(bystrikingwithahammer)tothe
structureatanappropriatelocationonit.
8.

WhatismeantbyForcedvibrations?

Forcedvibrationsareproducedinastructurewhenitisacteduponbythecontinuous
presenceofanexternaloscillatingforceactingonit.Thestructureunderforcedvibration
normallyrespondsatthefrequencyratio,i.e.(fm/fn)wherefmisthefrequencyofexcitation
andisthenaturalfrequencyofthestructure.
9.

WriteashortnoteonAmplitude.

Itisthemaximumresponseofthevibratingbodyfromitsmeanposition.
Amplitudeisgenerallyassociatedwithdirectionvertical,horizontal,etc.Itcanbeexpressedin
theformofdisplacement(u),velocity()oracceleration().Inthecaseofsimple harmonicmotion,

thesetermsarerelatedthroughthefrequencyofoscillation(f).
Ifuisdisplacementamplitude,then
Velocity()=2f.u
Acceleration()=(2f).(u)=4u
Whenaccelerationisusedasameasureofvibration,itismeasuredintermsof
accelerationduetogravity,g(9.81m/sec2).
10.DefineResonance.
Thisphenomenonischaracterizedbythebuildupareaoflargeamplitudesof
anygivenstructuralsystemandassuch,ithasasignificanceinthedesignof
dynamicallyloadedstructures.Resonanceshouldbeavoidedunderallcircumstances,whenevera
structureisacteduponbyasteadystateoscillatingforce(i.e.,fmisconstant).The presence of
damping,however,limitstheamplitudesatresonance.Thisshowstheimportanceofdamping
incontrollingthevibrationsofstructures.AccordingtoIS18931975Indianstandardcodeof
practice on Earthquake resistant design of structures,following values of dampingare
recommendedfordesignpurposes.

11.WhatismeanbyDegreesoffreedom?
Thenumberofdegreesoffreedomofsystemequalstheminimumnumberof
independentcoordinatesnecessarytodefinetheconfigurationofthesystem.
12.Definestaticforce.
Apushorpulloraloadormanyloadsonanysystemcreatesstatic
displacementordeflectiondependingonwhetheritisalumpedsystemoracontinues
system;thereisnoexcitationandhencethereisnovibration.
13.WriteashortnoteonsimpleHarmonicmotion.
Vibrationisperiodicmotion;thesimplestformofperiodicmotionissimple
harmonic.Morecomplexformsofperiodicmotionmaybeconsideredtobecomposedofa
numberofsimpleharmonicsofvariousamplitudesandfrequenciesasspecifiedin
Fourierseries
14.WhatistheresponseforimpulsiveloadorShockloads?
Impulsiveloadisthatwhichactsforarelativelyshortduration.Examplesare
impactofahammeronitsfoundation.Dampingisnotimportantincomputingresponseto
impulsive loads since the maximum response occurs in a very short time
beforedampingforcescanabsorbmuchenergyfromthestructure.Therefore,only
theundampedresponsetoimpulsiveloadswillbeconsidered.
15.Writeashortnoteonsingledegreeoffreedom(SDOF)systems.
Atanyinstantoftime,themotionofthissystemcanbedenotedbysingleco
ordinate(xinthiscase).Itisrepresentedbyarigidmass,restingonaspringofstiffnesskand
coupledthroughaviscousdashpot(representingdamping)havingconstantC.Here,
the mass m represents the inertial effects of damping (or energy dissipation) in the
system.Usingthedynamicequilibriumrelationwiththeinertialforceincluded,accordingto
DAlembertsprinciple,itcanbewrittenasmx+Cx+Kx=P
16.DefineCycle.
Themovementofaparticleorbodyfromthemeantoitsextremeposition inthedirection,then
tothe mean and then anotherextremepositionandbacktothe meanicalledaCycleofvibration.

CyclespersecondaretheunitHz.

17.

WriteshortnotesonDAlembertsprinciple.

AccordingtoNewtonslawm,F=ma
Theaboveequationisintheformofanequationofmotionofforceequilibriuminwhichthesum
ofthenumberofforcetermsequalzero.Henceifanimaginaryforcewhichisequaltomawere
appliedtosysteminthedirectionoppositetotheacceleration,thesystem couldthenbeconsideredto
beinequilibriumundertheactionofrealforceFandtheimaginaryforcema.Thisimaginaryforcemais
knownasinertiaforceandthepositionofequilibriumiscalleddynamicequilibrium.
DAlembertsprinciplewhichstatethatasystemmaybeindynamicequilibriumby addingtotheexternal

forces,animaginaryforce,whichiscommonlyknownastheinertiaforce
18.Writethemathematicalequationforspringsinparallelandspringsinseries
Springsinparallel

k =k k
e

k iscalledequivalentstiffnessofthesystem
e

Definelogarithmicdecrementmethod.
Logarithmicdecrementisdefinedasthenaturallogarithmicvalueoftheratioofadjacentpeak
valuesofdisplacementinfreevibration.Itisadimensionlessparameter.Itisdenotedbyasymbol
20.WriteshortnotesonHalfpowerBandwidthmethod.
Bandwidthisthedifferencebetweentwofrequenciescorrespondingtothesame
amplitude.Frequencyresponsecurveisusedtodefinethehalfpowerbandwidth.Inwhich,
thedampingratioisdeterminedfromthefrequenciesatwhichtheresponseamplitude.

21.DefineMagnificationfactor.
Magnificationfactorisdefinedastheratioofdynamicdisplacementatanytimetothedisplacement
producedbystaticapplicationofload.
22.Whatisthedifferencebetweenastaticanddynamicforce?
Inastaticproblem,loadisconstantwithrespecttotimeandthedynamicproblemis
thetimevaryinginnature.Becausebothloadinganditsresponsesvarieswithrespectto
time
Staticproblemhasonlyoneresponsethatisdisplacement.Butthedynamicproblem hasmainlythree

responsessuchasdisplacement,velocityandacceleration.
23.Definecriticaldamping.
Criticaldampingisdefinedastheminimumamountofdampingforwhichthesystemwillnot
vibratewhendisturbedinitially,butitwillreturntottheequilibrium
position.Thiswillresultinnonperiodicmotionthatissimpledecay.Thedisplacement
decaystoanegligiblelevelafteronenatureperiodT.
24.Listoutthetypesofdamping.
(1)

ViscousDamping,(2)CoulombDamping,(3)StructuralDamping,(4)Active

Damping,(5)PassiveDamping.
25.Whatismeantbydampingratio?
Theratiooftheactualdampingtothecriticaldampingcoefficientiscalledasdampingratio.It
isdenotedbyasymbolanditisdimensionlessquantity.

PARTB

1. DerivetheequationofmotionofSDOFsystemforfreevibration&hencefindthesolution
for
i)
Underdampedsystem
ii)
Criticallydampedsystem
iii) Overdampedsystem

UINTII
1.

Definedegreesoffreedom.

Theno.ofindependentdisplacementsrequiredtodefinethedisplacedpositionsof
allthemassesrelativetotheiroriginalpositioniscalledtheno.ofdegreesoffreedomfor
dynamicanalysis.
2.

Writeashortnoteonmatrixdeflationtechnique.

Whenever the starting vector, the vector iteration method yields the same lowestEigen
value.Toobtainthenextlowestvalue,theonealreadyfoundmustbesuppressed.Thisis
possiblebyselectingvectorthatisorthogonaltotheeigenvaluesalreadyfound,orbymodifying
anyarbitrarilyselectedinitialvectorformorthogonaltoalreadyevaluatedvectors.TheEigevecto
XcomputedbyiterationasinthepreviousexampleXwouldbeorthogonaltotheXL1.
thecorrespondingfrequencywillbehigherthanL1butlowerthanallotherEigenvalues.
4.

Whatismeanbyflexibilitymatrix

Correspondingtothestiffness(k),thereisanotherstructuralpropertyknown
asflexibilitywhichisnothingbutthereciprocalofstiffness.TheflexibilitymatrixFisthusthe
inverseofthestiffnessmatrix,[F]=[K]1.
5.

WriteashortnoteonJacobisMethod.

WhileallotherenableustocalculatethelowestEigenvaluesoneafteranother,
JacobismethodyieldsalltheEigenvaluessimultaneously.Byaseriesoftransformationsofthe
classical form of the matrix prescribed by Jacobi, all thenon diagonal terms may be
annihilated,thefinaldiagonalmatrixgivesalltheEigenvaluesalongthediagonal.
6.

Whatarethestepstobefollowedtothedynamicanalysisofstructure?

Thedynamicanalysisofanystructurebasicallyconsistsofthefollowingsteps.
1.Idealizethestructureforthepurposeofanalysis,asanassemblageof
discreetelementswhichareinterconnectedatthenodalpoints.
2.Evaluatethestiffness,inertiaanddampingpropertymatricesoftheelementschosen.
3.By supporting the element property matrices appropriately, formulate thecorresponding
matricesrepresentingthestiffness,inertiaanddampingofthewholestructure.

7.

WriteashortnoteonInertiaforceMassmatrix[M]

Onthesameanalogy,theinertiaforcescanberepresentedintermsofmass
influencecoefficient,thematrixrepresentationofwhichisgivenby{f1}=[M]{Y}
MijatypicalelementofmatrixMisdefinedastheforcecorrespondingtocoordinateidueas
theforcecorrespondingtocoordinateiduetounitaccelerationappliedtothecoordinatej.
[M]{Y}+[C]{Y}+[K]{Y}={P(t)}

8.

WhataretheeffectsofDamping?

Thepresenceofdampinginthesystemaffectsthenaturalfrequenciesonlytoa
marginal extent. Itisconventionalthereforetoignoredampinginthecomputationsfornatural
frequenciesandmodeshapes
9.

WriteashortnoteondampingforceDampingforcematrix.

Ifdampingisassumingtobeoftheviscoustype,thedampingforcesmay likewiseberepresented

by means of a general damping influence co efficient, Cij. Inmatrixformthiscanbe

representedas
{fD}=[C]{Y}

10.Whatarethestepstobefollowedtothedynamicanalysisofstructure?
Thedynamicanalysisofanystructurebasicallyconsistsofthefollowingsteps.
1.Idealizethestructureforthepurposeofanalysis,asanassemblageof
discreetelementswhichareinterconnectedatthenodalpoints.
2.Evaluatethestiffness,inertiaanddampingpropertymatricesoftheelementschosen.
3.By supporting the element property matrices appropriately, formulate the corresponding
matricesrepresentingthestiffness,inertiaanddampingofthe wholestructure.

11.

Whatarenormalmodesofvibration?

Ifintheprincipalmodeofvibration,theamplitudeofoneofthemassesisunity,itisknownas
normalmodesofvibration.
12.DefineShearbuilding.
Shearbuildingisdefinedasastructureinwhichnorotationofahorizontalmemberathefloor
level.Sinceallthehorizontalmembersarerestrainedagainstrotation,thestructurebehaveslikea

cantileverbeamwhichisdeflectedonlybyshearforce.
PartB
1. Explainindetailaboutmodesuperpositionmethod.
2. Determinethenaturalfrequencyandthemodeshapesforthefollowingshearbuilding

3. DeterminethenaturalfrequenciesandthemodeshapesofthegivenMDOFSystem
.EI=4.5x106Nm2forallcolumns,

UNITIII
1.

DefineSeismology.AndEarthquake

Seismologyisthestudyofthegeneration,propagationgenerationandrecordingofelasticwavesin
theearthandthesourcesthatproducethem.
An Earthquake isa sudden tremor or movement of the earthscrust,whichoriginates
naturally at or below the surface. About 90% of all earthquakes results from tectonic events,
primarilymovementsonthefaults.
2.

WhatarethecausesofEarthquake?

Earthquakeoriginatesduetovariousreasons,whichmaybeclassifiedintothree
categories.Deckingwavesofseashores,runningwaterdescendingdownwaterfallsand
movementofheavyvehiclesandlocomotives,causesfeebletremorstheseearthquakes
arefeebletremors,whichdonthavedisastrouseffects.
Contrary to the volcanic earthquake and those due to superficial causes,which can be
severe,onlylocally,themoredisastrousearthquakesaffectingextensive regionareassociated

with movements of layers or masses of rocksformingthecrustoftheearth.Suchseismic

shocks,whichoriginateduetocrustalmovements,aretermedastectonicearthquakes.
3.

WhatismeanbyEpicenterandfocus?

Thepointatwhichtherupturebeginsandthefirstseismicwaveoriginatesiscalledfocusor
hypocenter.Thepointonthegrounddirectlyabovethefocusiscalledepicenter.
4.

WriteashortnoteonPlateTectonicTheory

Tectonicisthestudyofdeformationsofearthmaterialsthatresultfrom
deformation.Platetectonicsreferstodeformationonaglobalscale.Thebasichypothesisofplate
tectonicsisthatthesurfaceoftheearthconsistsofanumberoflargeplates.Theseplates
moverelativetooneanother.Thepresentsiximportantplatesarenamely
1.Africanplate
2.Americanplate
3.Antarcticplate

4.AustralianIndianplate
5.Eurasianplate
6.Pacificplate
5.

WriteashortnoteonSeismicwaves.

Largestrainenergyreleasedduringanearthquaketravelasseismicwavesinall
directionsthroughtheearthslayers,reflectingateachinterface.Thesewavesareaoftwo
types,bodywavesandsurfacewaves
6.

WriteashortnoteonMagnitude.

Themagnitudeofanearthquakeisameasureoftheamountofenergyreleased.The
earthquakescaleisdevisedbyCharlesF.Richter,anAmericanseismologistbebasedonthetota
lamountofenergyreleasedanearthquakebecalledmagnitude.
7.

Whatismeanbyseismogram?

Aseismogramisthegraphoutputbyaseismograph.Itisarecordofgroundmotion
atameasuringstation.Theenergymeasuredinaseismogrammayresultfromearthquake
orfromsomeothersource.
8.
WriteanoteonIntensity.
Intensityindicatestheintensityofshakingorextentofdamageatagivenlocationdueto
particular earthquake. Thus theintensity of some earthquakewill bedifferent at different
places.Intensityisameasureearthquakeinqualitativewaybyjudgingwhatactuallyhappensontheground,
thedamagetothebuildingsandotherstructurescausedbyearthquake waves.

9.WhatisElasticreboundtheory?
TheconceptofpossiblemodeoforiginoftectonicearthquakesisknownasElastic
Reboundtheory.
10.

Namethetypesoffault.

(i)DipSlipfault
(ii)StrikeSlipfault
(iii)ObliqueSlipfault
11.

WhatarethetypesofDipSlipfault?

DipSlipfaulthavingtwotypestheyare
(i)Normalfault
(ii)Reversefault

12.

WhatarethetypesofBodywavesandsurfacewaves?

Bodywavesaremainlyoftwotypes,theyare
(i)Primarywaves(or)Pwaves
(ii)Secondarywaves(or)Swaves
Surfacewavesalsohavingtwotypes,theyare
(i)Lovewaves
(ii)Rayleighwaves
15.

WhatisthedifferencebetweenInterplateearthquakesandIntraplate

earthquakes?
(i)Interplateearthquakes:Theearthquakeoccurringalongtheboundariesof

thetectonicplatesarecalledasinterplateearthquakes.
Example:1987,AssamEarthquake
(ii)Intraplateearthquakes:Theearthquakesoccurringwithinaplatearecalled
asintraplateearthquakes.
Example:1993,LaturEarthquake
16.

Whatarethefactorsinfluencesthegroundmotion?

Thefactorswhichinfluencethegroundmotionare:
(i)Magnitudeofearthquake
(ii)Epicentraldistance
(iii)Localsoilconditions
17.

Whatisthedifferencebetweenshallow,intermediateanddeepfocusearthquake?

(i)Shallowfocusearthquake:Inthiscase,theseismicshocksoriginateatadepthofabout
lessthan70km.Nearly80%oftheworldsearthquakesareshallowfocusearthquakes.
(ii)Intermediatefocusearthquake:Inthiscase,theseismicwavesoriginateatadepthbetween70
kmto300km.
(iii)Deepfocusearthquake:Here,thepointoforiginoftheseismicwaveisata
depthofgreaterthan300km.
18.

WhatisSeismograph?

Seismographisaninstrumentusedtorecordingmotionsoftheearthssurface

causedbyseismicwaves,asafunctionoftime.Amodernseismographincludesfivebasicparts:a

clock,asensorcalledaseismometerthatmeasuresintensityofshakingattheinstruments
location,arecorderthattracesachartorseismogram,oftheseismicarrivals,anelectronicamplifier
andadatarecorderthatstorestheinformationforlateranalysis.
19.

ExplainvolcanicEarthquake?

Earthquakesassociatedwithvolcanoesaremorelocalizedbothintheextentof
damageandintheintensityofthewavesproducedincomparisontothosewhichare
associatedwithfaultingmotions.Deepbelowthecentreofvolcano,hotmagmamoves slowly
throughundergroundpassagesunderpressure,asitsmakesitwaystowardsthe earthssurface.As

thishappens,thesurroundingrockisputunderpressureasthemagmapushesagainstit.Thiscauses
therocktofractureandsmallearthquakestooccur.
20.

WhatarethebasicdifferencebetweenFocusandEpicentre?

Focusisthelocationwithintheearthwherefaultruptureactuallyoccurswhereastheepicentreis
thelocationonthesurfaceabovethefocus.
21.

Whatishypocenter?

Focusisanexactlocationwithintheearthwhereseismicwavesaregeneratedby
suddenreleaseofstoredelasticbuilding.Itiscalledashypocenter.
22.

Whatisaccelerogram?

Agraphplottedbetweenaccelerationofgroundandtimeiscalledaccelerogram.Thenatureof
accelerogramsmayvarydependingonenergyreleasedatfocus,typeoffaults,geologyalong
thefaultplaneandlocalsoil.
23.

ExplainUttarkashiearthquakeof1991?

Anearthquakeofmagnitude6.6struckthedistrictsofUttarkashi,Tehriand
ChamoliinthestateofUttarPradeshonOctober20,1991.About768personslosttheir
lives,withabout5,066injured.Maximumpeakgroundaccelerationofabout0.31gwas recordat

Uttarkashi.ManyfourstoreybuildingsinUttarkashiwithRCframeandinfill wallssustained
theearthquake.Howeever,someoftheordinaryRCbuildingscollapsed.

24.

EnumerateTSUNAMI.

A tsunami is a wavetrain or series of waves, generated in a body of water by an

impulsivedisturbancethatverticallydisplacesthewatercolumn.TsunamiisaJapanese word
withthe English translation, harbourwave. The term tsu means harbourand nami means
wave.Tsunamicanbegeneratedwhentheseafloorabruptlydeformsandverticallydisplaces
the overlaying water. Tectonic earthquakes are a particular kind ofearthquakes that are
associatedwiththeearthscrustaldeformation;whentheseearthquakesoccurbeneaththesea,the
waterabovethedeformedareaisdisplacedfromtheequilibriu position.Waves are formedas the
displaced watermass,whichactsinfluenceof gravity. Whenlargeareasoftheseafloorelevateor
subside,atsunamicanbecreated.
25.

WhatisFocaldepthandEpicentraldistance?

(i)Focaldepth:Thedistancebetweentheepicentreandthefocusiscalledfocal
depth.
(ii)Epicentraldistance:Thedistancefromepicentretoanyofinterestiscalled
epicentraldistance.
PartB
1.WriteashortnoteonprimaryshearandRayleighwaves.
2.Explainaboutseismographwithneatsketch.
3.Explainindetailaboutmagnitudeandintensityofearthquake.
4.Averticalcable254cmlonghasacrosssectionalareaof3.23cm 2,supportsaweightof
4536kg.Whatarethenaturalfrequency,cyclefrequencyandtimeperiodofthesystem,ifitis

undervibrationE=2.1x106kg/cm2.
5.Acantileverbeamissupportingaweightof4536kg.Lengthofcantileverbaris254cm,What

arethenaturalfrequency,cyclefrequencyandtimeperiodofthesystem,assumeE=2.1x106
kg/cm2,I=1171.27cm4.
6.Avibratingsystemconsistsofweight=9.81kN.Ifaspringofstiffness20kN/cmanddamping
constantof0.071kNsec/cmfind

i.

Dampingratio

ii.

Dampedfrequency

iii.

Logarithmicdecrement

iv.

Ratioofanytwoconsecutiveamplitudes.]

7.Formulatetheequationofmotionfortwostoreyedshearframegiveninfigure.Drawthefree
bodydiagramanddeterminethemassandstiffnessmatrix.Thesystemisundamped.

UNITIV
PARTA
1.

Whatdoyouunderstandbyresponsespectrum?

A Responsespectrumisthe plot of themaximumresponse(maximudisplacement,velocity,

accelerationoranyotherquantityofinterest)toaspecifiedloadfunctionXa(t)forall
possible SDOF systems (having differentnaturalfrequenciesortimeperiodsTandaconstant
dampingratio).
2.

Whatismeanbysoilliquefaction?

Soilliquefactionduringanearthquakeisaprocessthatleadstolossofstrength
orstiffnessofthesoil.Thiscouldresultinthesettlementofstructures,causelandslides,precipitates
failuresofearthdamsorcauseothertypesofhazards.Soilliquefaction hasbeenobservedtooccur

mostofteninloosesaturatedsanddeposits.
3.

Writeashortnoteonliquefactionofclaysoil.

Certainclayeysoilsarevulnerabletoservestrengthlossduetoearthquakeshaking.
Aclayeysoilwouldbeconsideredliquefiableifallofthefollowingcriteriaaremet:
Theweightofthesoilparticlesfinerthan0.005mmislessthan15%ofthedry
weightofthesoil.
ii.Theliquidlimitofthesoilisless35%.
iii.Themoisturecontentofthesoilislessthan0.9timestheliquidlimit.
4.

HowtheliquefactioninducedGroundfailures?

Ifasoilbecomesliquefiedandlosesitsshearstrength,groundfailuresmay
result.Whenstructuresarefoundedoverornearthesesoildeposits,theymayget damaged.The

groundfailurescausedbyliquefactionmaybeclassifiedintothefollowingcategories:
i.FlowFailures
ii.LossofBearingCapacity
iii.LateralSpreading

5.

Whatdoyouunderstandbylateralspreading?

Lateralspreadingisthemovementofsurfacialsoillayers,whichoccurthereis
alossofshearstrengthinasubsurfacelayerduetoliquefaction.Lateralspreadingusuallyoccursonvery
gentleslopes(<6%).Ifthereisdifferentiallateralunderastructure,therecouldbesufficienttensile
stressesdevelopedinthestructuresthatitcouldliterallytearapart.Flexiblebuildingshavebeen
observedtobetterwithstandextensionaldisplacement thanmorestifforbrittlebuildings.

6.

WhatarethemethodsavailableonsiteModification?

Severalsitemodificationmethodshavebeendevisedandadoptedtoreducethe

potentialorsusceptibilityofthesoilsbeneathasitetoliquefy.Someoftheminclude
ExcavationandReplacementofliquefiablesoils

Densificationofinsitusoils

Instuimprovementofsoilsbyalteration

GroutingorchemicalStabilization.

7. WriteashortnoteonSoilAlteration?
Thethirdmajorcategoryofsiteimprovementmethodsisalterationofthesoilto
reducethepotentialforliquefaction.Thesoilmaybemademoreresistantbytheconstructionof
mixedinplacesolidifiedpilesorwallstoprovideshearresistancewhich wouldconfineanareaof

liquefiablesoilstopreventflow.
8.

WhatismeanbyGrouting?

Thefourthcategoryofsoilimprovementmethodsissoilgroutingor
chemical stabilization.These would improve the shear resistance of the soils by injection of
particulatematter,resinsorchemicalsintothevoids.Commonapplicationsarejetgroutingand
deepsoilmixing.
9.

WhatismeanbyStructuralDamping?

Dampingofstructuralsystemsplaysamajorroleindeterminingthe
responseofthestructureforgroundmotionsinducedbyearthquakes.Theactualstiffness
offoundationanddampingcoefficientaredependentonthefrequencyofvibration.

10.

WhataretheeffectsofDampingonsoilstructureinteraction?

Simplesingledegreeoffreedom(SDOF)systemisconsideredforthe
analysis.Thesystemismountedonarigid,masslessandLShapedfoundationwhichin
turnissupportedonanelasticfoundation.
11.

DefineDuctility.

Theabilityofastructureoritscomponentsorofthematerialsusedtooffer
resistanceintheinelasticdomainofresponseindescribedbythetermDuctility.It
includestheabilitytosustainlargedeformations,andacapacitytoabsorbenergy
hystereticbehavior.
12.

Whatarethebasicconceptsforductileperformancestructures?

i.Selectionofsoundstructuralconfigurationwithawelldefinedlateralloadresistingsystem.
ii.Systematicplacementofstiffelementswithaviewtominimizeincreaseinmember
forcesduetotorsion.
iii.,Availabilityofdirectloadpathforforcetransferfromsuperstructuretosoilmedium.
iv.Properdetailingofmembersandjointsisverymuchnecessary
13.

WriteashortnoteonPushoveranalysis.

Pushoveranalysisisastaticanalysisprocedureforassessingthecapacityofstructuralmembers
againstseismicforces.Anumberofwidelusedprocedures(FEMA273,ATC40)comparethes
demandswiththerecommendedvaluesofmembercapacitiesvaryingwiththelevelof
the performance objectives employed. Each member is classified as either force based or
displacementbased,dependingonitsmodeofbehavior.
14.

MentionthedifferentVariableaffectingsectionalductility.

Thevariablesthataffectsectionalductilityinclude,
i.Materialvariablessuchasthemaximumusablecompressivestrainin
concreteandgradeofreinforcement.
ii. Geometricvariablessuchastheamountoftensionandcompression
reinforcementandtheshapeofthesection.
iii.Loadingvariablessuchasthelevelofaxialloadaccompanyingshear.

15.

WhatdoyouunderstandbyResponsereductionfactor(R)?

Itisthefactorbywhichtheactualbaseshearforce,thatwouldbe
generated if the structure were to remain elastic during itsresponse to design basis
Earthquakeshaking,shallbereducedtoobtainthedesignlateralforce.Ductilebuildings are
designedforseismicforcesthatareRtimeslowerthantheelasticbehaviorwould require.

16.

WriteaShortnotesontheAnalysisofstructuralResponseBasedonSoil

properties.
Analysisofsoilstructureinteractioncanbeeitherusingthedirectmethodorthemultiplestepmethod.
Inthedirectmethod,finiteelementmodelofthesoilfoundation systemisgeneratedandsolvedina

singlestep.Multistepmethodofanalysisusestheprincipleofsuperpositiontoisolatethe
twoprimarycausesofsoilstructureinteraction,
a)theinabilityofthefoundationtomatchfreefielddeformation;
b)theeffect of dynamicresponseoffoundationstructuresystemonthemovementofthe
supportingsoil.
17.

Whatiszeroperiodacceleration?

Zeroperiodaccelerationimpliesmaximumaccelerationexperiencedbyastructurehavingzero
naturalperiod(T=0).Aninfinitelyrigidstructurehaszeronaturalperiod(T=0).Itdoesn t
deform.Thusrelativemotionbetweenitsmassanditsbase,Masshassameaccelerationasof
theground.HenceZPAisthesameaspeakgroundacceleration.
18.

Whatisadesignspectrum?

Responsespectrumdevelopedfordisplacement,pseudovelocityandpseudo
accelerationinacombinedmannerforelcentroearthquake(1940)forvariousdamping
ratios.Thistypeofspectrumcalledtripartiteresponsespectrum.Fordesignpurpose,local
peaksandvalleysshouldbeignored,sincenaturalperiodcantbecalculatedwithaccuracy.
Hencesmoothcureplottedbyconsideringtheaveragenumberofelasticresponsespectrums
correspondingtovariouspossibleearthquakesatparticularsite.Itisknownasdesign
spectrum.

19.

Whatispeakgroundacceleration(PGA)?

PGAisameasureofearthquakeacceleration.UnlikeRichterscale,itisnotameasureofthetotal
sizeoftheearthquake,butratherhowhardtheearthshakesinagivengeographicalarea.PGAis
whatisexperiencedbyaparticleontheground.
20.

Enumeratesitespecificresponsespectrum.

Asitespecificresponsespectrumisplottedbytakingtheaverageofeachrecordofsitespecific
groundmotions.Thisresultsinsmoothmeansspectrum.Therecordedearthquakemotionsclearly
showthatresponsespectrumshapediffersfordifferenttypesof soilprofileatthesite.Seed,Ugasand
Lysmer(1985)plottedtheaverageshapeofresponse ofspectrum.

21.

Whatarethemethodstoreduceliquefaction?

(a)Avoidliquefactionsusceptiblesoils
(b)Buildliquefactionresistantstructures
(c)Shallowfoundationaspects
(d)Deepfoundationaspect
(e)Improvethesoil
(f)Drainagetechniques
(g)Verificationofimprovement
22.

Listouttheeffectsofliquefaction.

(a)Lossofbearingstrength
(b)Lateralspreading
(c)Sandboils
(d)Flowfailures
(e)Groundoscillation
(f)Flotation
(g)Settlement.
23.

Nametwotypeofliquefaction.

Liquefactionhastwotypestheyare
(i)

Flowliquefaction

(ii)Cyclicmobility.

24.

Whatispounding?

Poundingisanotherimportantissueintheconstructionofmultistoryframeinurbanareas.Thatis
whentwomultistoryframesareconstructedtooclosetoeachother;they maypoundoneachother
duringstronggroundmotionwhichleadstocollision.Toavoid collection,adjacentbuildingsshouldbe

separated by minimum gab. These factors imply that nowadays there is a need of earthquake
resistancearchitectureinhighlyseismicareas.
25.

Namethefourtechniquesofaseismicdesign.

Thefollowingfourtechniquesofaseismicdesignorearthquakeresistantbuilding
are:
(a)Structuralconfiguration
(b)Lateralstrength
(c)Goodductility
(d)Lightweightmass
PartB
(i) WriteashortnoteonDesignSpectrum.
(ii) Mentiontheeffectsofsoilpropertyanddampingonseismicperformanceofstructure.
(iii) ExplainSoilliquefactionprocessindetailalongwithitseffectsandconsequences.

UNITV
PARTA

1.

Whatistheformulatofindtheloadfactorsforplasticdesignofsteelstructures?

Inplasticdesignofsteelstructures,thefollowingloadcombinationsshallbe
accountedfor
1.1.7(DL+IL)
2.1.7(DL+EL)
3.1.3(DL+IL+EL)
WhenEarthquakeforcesareconsideredonastructure,theseshallbecombinedasperLoad
combinationforplasticdesignofsteelstructuresandpartialsafetyfactorforlimit
statedeignofRCandPSCstructures.
2.

WhatarethemethodsofimprovingelementlevelDuctility?

Ductility in element level is generally with reference to the displacementandmoment

curvaturerelationshipofasection.Thiscanbegenerallyimprovedby

Decreasingthetensionsteelarea,yieldstressandstrainofthetensionsteel

increasingtheultimatecompressivestrainofconcrete.

Increasingtheareaofcompressionsteel.

Reductionintheaxialcompressiononthesection.
Provisionofeffectiveconfinementstirrups,hoopsortiessuchthat
compressivesteeldoesnotbuckleandconcreteisledintothreedimensional
stateofstresssuchthatitsultimatecompressivestrainincreases.
3.
WritetheIS13920provisionsforflexuralmembers.
Theprovisionsapplytoframemembersresistingearthquakeinducedforcesanddesignedtoresist
flexure.Thesemembersshallsatisfythefollowingprovisions
(a)Thefactoredaxialstressonthememberunderearthquakeloadingshallnotexceed0.1fck.
(b)Themembershallpreferablehaveawidthtodepthratiomorethan0.3
(c)Widthofthemembershallnotbelessthan200mm.
(d)ThedepthDofthemembershallpreferablybenotmorethanofclearspan.

4.

WhatistheformulaforfindingouttheBaseshearusingseismiccoefficientmethod?

VB=KChW
Where,
VB=isbaseshear,Kisperformancefactor
Cisacoefficientdependingontheflexibilityofthestructure
hisdesignseismiccoefficient.
5.

WriteashortnotesonReviewofIndianCodeIS1893(1984)

IS1893(1984)givestheNecessarycriteriafortheearthquakeresistantdesignof structures.This
code states that structures should withstand without structural damage, moderate earthquakes and

withstandwithouttotalcollapse,heavyearthquakes.
Thiscodespecifiestwomethodsofanalysis
i.Seismiccoefficientmethod
ii.ModalanalysisorResponseSpectrummethod.
6.

Whatarethestructuralprotectivesystems?

Modernprotectivesystemisbasedon(i)Seismicbaseisolation(ii)Passiveenergydissipaters(iii)
Semiactiveandactivesystems.Passiveenergydissipatersareclassifiedashysteric,designseismic
coefficientdesignseismiccoefficientViscoelasticandothersbasedonthedevicesused.Eg
yieldingofmetalsthroughslidingfriction
7.
WriteashortnoteonMechanismofBaseisolation.
The Mechanism of base isolation subjected to ground motion. The isolation reduces the
fundamentallateralfrequencyofthestructurefromitsfixedbasefrequencyandthusshiftstheposition
ofstructureinthespectrumfrompeakplateauregion.Alsoitbringsforthadditionaldampingduetothe
increased damping introduced at the base level andthusreductioninthespectralaccelerationis

achieved.
8.

WritedownthestepstoimproveGloballevelDuctility?

(a)Increasingtheredundancyofthestructure
(b)Weakbamandstrongcolumnapproach.
(c)Avoidingsoftfirststoreyeffects
(d)AvoidingNonductilefailuremodeslikeshear,bondandaxialcompressionattheelement
level
9.

Definelateralloadanalysisofbuildingsystem.

Earthquakeforceisaninertiaforcewhichisequaltomasstimesacceleration.
Mass of the building is mainly located at its floors. Transferring the horizontal component of
seismicforcesafelytothegroundisthemajortaskinseismicdesign.Thefloorsshould

transfer the horizontal force to vertical seismic elements viz., columns, frames, walls and
subsequentlytothefoundationfinallytothesoil.
10.

WriteashortnoteonIndianseismiccodes.

ThecodesensuresafetyofbuildingsunderearthquakeexcitationIS18931962,
recommendationsforearthquakeresistantdesignofstructures.IS18931984thecountryhas
dividedintofivezonesinwhichonecanreasonablyforecasttheintensityofearthquakeshock
whichwilloccurintheeventoffutureearthquake.
11.

DefinethetermDBE,MCEandMMI.

DBE:DesignBasicsEarthquake
MCE:MaximumConsideredEarthquake
MMI:MercalliIntensityScale.

12.

Whatisthedesignphilosophyadoptedforearthquakeresistantstructure?

Theextremeconditioncausedbyanearthquakeandalsothelowprobability of such an event

occurring within the expected life of astructure,the followingdualdesignphilosophyisusually

adopted structure is designed to resist the expected intensity of ground motiondue to a

moderateearthquakesothatnosignificantdamageiscausedtothebasicstructureandThe
structureshouldalsobeabletowithstandandresisttotalcollapseintheunlikelyeventofa
severeearthquakeoccurringduringitslifetime.Thedesigneriseconomicallyjustifiedinthis
casetoallowsomemarginaldamagebuttotalcollapseandlossoflifemustbeavoided.

13.

WritedowntheformulatofindouttheMagnitudeaspertheIScode.

Theamountofstrainenergyreleasedat the source is indicated bythe magnitudeofthe

earthquake.
Magnitude=Log10(Amax)
WhereAisthemaximumaptitudeinmicrons(103m)recordedbyWood
Andersonseismograph.IfEistheenergyreleased,then
LogE=11.8+1.5M

14.

Whatdoyouunderstandbyresponsespectrum?

AResponsspectrumistheplotofthemaximumresponsmaximum
displacement,velocity,accelerationoranyotherquantityofinterest)toaspecifiedloadfunctionXa
(t)forallpossibleSDOFsystems(havingdifferentnaturalfrequenciesortimeperiodsTanda
constantdampingratio).
15.Whyisbaseisolationeffective?
Thebaseisolationsystemsreducethebaseshearprimarilybecausethenaturalvibrationperiodof
theisolationmode,providingmostoftheresponse,ismuchlongerthan thefundamentalperiodofthe
fixedbasestructure,leading to amuchsmaller spectralordinate.Thehighermodesaessentiallynot
excitedbythegroundmotion;althoughtheir accelerationislargetheirmodalstaticresponsesarevery

small.
16.Explaintwocasesofdesignhorizontalearthquakeload.
(a)Whenthe lateralresistingelementsare oriented alongorthogonal horizontaldirection,the
structureshall bedesignedfortheeffectsdueto full designearthquakeloadinonehorizontal
directionattime.
(b) When the lateral load resisting elements are not oriented along the orthogonal horizontal
directions,thestructureshallbedesignedfortheeffectduetofulldesignearthquakeloadinone
horizontaldirectionplus30%ofthedesignearthquakeloadintheotherdirection.
PartB
1. Explainindetailaboutmodesuperpositionmethod.
2. Determinethenaturalfrequencyandthemodeshapesforthefollowingshearbuilding

3.DeterminethenaturalfrequenciesandthemodeshapesofthegivenMDOFSystem
.EI=4.5x106Nm2forallcolumns,