土木工程專業(yè)英語 課件 6.1 Earthquake-Induced Vibration of Structures

6.1Earthquake-InducedVibrationofStructuresTopicsSeismicityandGroundMotionsInfluenceofLocalSiteConditionsResponseofStructurestoGroundMotionsSeismicityandGroundMotionsTheearthismadeupoffourlayers,thecrust,themantle,theoutercore,andtheinnercore.Lithosphereisbrokenintoanumberoftectonicplates.

Tectonicplates

arerigid,relativelycoolslabsabout100kmthick

consistoftheearth'scrustandlithosphere.Tectonicplates

構(gòu)造板塊floatonthemolten

mantle（asthenosphere軟流圈）oftheEarthandmoverelativetooneanotherattherateof10to100mm/year.The6,000-km-plusjourneyoftheIndialandmass(IndianPlate)beforeitscollisionwithAsia(Eurasian[juE5reiViEn]歐亞大陸Plate)about40to50millionyearsago.IndiawasoncesituatedwellsouthoftheEquator[i5kweitE],nearthecontinentofAustralia.Iftheplatesarepushingtogether,oneplatetendstodiveundertheotherand,dependingonthedensityofthematerial,itmayresurfaceintheformofmountainsandvalleys.*Insomecases,theplatemarginsaremovingawayfromoneanother.Inthosecases,moltenrockappearsfromdeepintheEarthtofillthegap,oftenmanifestingitselfasvolcanoes.*Anotherpossibilityisthattheplateboundarieswillslidesidewayspasteachother,essentiallyretainingthelocalsurfaceareaoftheplate.pullapart平滑斷層，橫向斷層*Thebasicmechanismcausingearthquakesintheplateboundaryregionsappearstobethatthecontinuingdeformationofthecrustalstructureeventuallyleadstostresses/strainswhichexceedthematerialstrength.Rocksfracture.Thesefracturesarecalledfaults.*ArupturewilltheninitiateatsomecriticalpointalongthefaultlineandwillpropagaterapidlythroughthehighlystressedmaterialattheplateboundaryItisbelievedthatapproximatelythreequartersoftheworld’searthquakesareaccountedforbythisrubbing–striking–slippingmechanism,withrupturesoccurringonfaultsonboundariesbetweentectonicplates.Suchearthquakesarereferredtoas

interplate

earthquakes

邊緣地震.Intraplateearthquakes板內(nèi)地震*Earthquakesalsooccuratlocationsawayfromtheplateboundaries.Sucheventsareknownasintraplateearthquakes板內(nèi)地震

andtheyaremuchlessfrequentthaninterplateearthquakes.*Earthquake-occurrencemapsusuallyindicatethelocationofvariousepicentersofpastearthquakes*theseepicentersarelocated(確定

，找出)byseismological[7saizmE5lCdVikEl]adj.

地震學(xué)上的

analysisoftheeffectofearthquakewavesonstrategicallylocatedreceivinginstrumentscalledseismometers[saiz5mCmitE]n.

測震儀.EnergyspreadsoutthroughtheearthindifferentwavetypesP-Waves

S-Waves

SurfaceWaves*Whenanearthquakeoccurs,severaltypesofseismicwaveareradiatedfrom自...發(fā)出therupture.Themostimportantofthesearethebodywaves(primary(P)andsecondary(S)waves).

Magnitudeoftheearthquake*Thetotalstrainenergyreleasedduringanearthquakeisknownasthemagnitudeoftheearthquake

震級

anditismeasuredontheRichterscale*Richterscaleisdefinedquitesimplyastheamplitude

振幅

oftherecordedvibrationsonaparticularkindofseismometerlocatedataparticulardistancefromtheepicenter.Modernseismometers(orseismographs)providedigitized

[5didVitaiz]將資料數(shù)字化orgraphicalrecordsofearthquake-inducedaccelerations加速度

inboththehorizontalandverticaldirectionsataparticularsite.Accelerometersproviderecordsofearthquakeaccelerationsandtherecordsmaybeappropriatelyintegratedtoprovidevelocityrecordsanddisplacementrecords.Peakaccelerations,velocities,anddisplacementsareallinturnsignificantforstructuresofdifferingstiffness.Therecordingoftheaccelerationofthegroundduringanearthquake.Acceleration,Velocity,DisplacementIntensity

Ameasureoftheeffect,orthestrength,ofanearthquakehazardataspecificlocationbasedonobservedhumanbehaviorandstructuraldamage.*Thelocalintensity

ofaparticularearthquakeismeasuredonthesubjectiveModifiedMercalliscalewhichrangesfrom1to12唐山7.8級地震等震線圖唐山7.8級地震等震線圖ModifiedMercalliscaleAmeansbywhichdamagemaybeassessedafteranearthquake.

albeit[C:l5bi:It]雖然subjectiveandqualitative,regionsofvaryingseismicriskmaybeidentified.usedtoassistinthedelineation

[dI9lInI`eIFEn]

描繪

oftheseregions.InfluenceofLocalSiteConditionsLocalgeological

地質(zhì)的

andsoilconditionsmayhaveasignificantinfluenceontheamplitudeandfrequencycontentofgroundmotions.InteractionbetweenthebedrockearthquakemotionandthesoilcolumnwillmodifytheactualgroundaccelerationsinputtothestructureThesoilpropertiesintheproximity[prCk5simiti]

鄰近ofthestructurecontributesignificantlytotheeffectivestiffnessofthestructuralfoundation.

strength(andresponse)ofthelocalsoilunderearthquakeshakingmaybecriticaltotheoverallstabilityofthestructure.ResponseofStructurestoGroundMotionsTheeffectofgroundmotiononthevariouscategoriesofstructuresisdictatedalmostentirelybythedistributionofmassandstiffnessinthestructure.Itisimportanttoappreciatethat,inanearthquake,loadsarenotappliedtothestructure.Rather,earthquakeloadingarisesbecauseofaccelerationsgeneratedbythefoundationlevel(s)ofthestructurebeinginfluencedbytransientgroundmotions.Specifically,theproductofthestructuralmassandthetotalaccelerationproducestheinertialoadingexperiencedbythestructure.

thetotalaccelerationistheabsoluteaccelerationofthestructure,namely,thesumofthegroundaccelerationandthatofthestructurerelativetotheground.Stiffstructurelittleadditionalaccelerationrelativetothegroundmotionearthquakeloadingexperiencedisessentiallyproportionaltothebuildingmass.Flexiblestructures(high-riseorlong-span)absoluteaccelerationislowThisoccursbecausethegroundaccelerationandtheaccelerationofthebuildingrelativetothegroundtendtoopposeoneanother.