高層建筑結(jié)構(gòu)設(shè)計(jì)第6章

Chapter6OtherLoadsThermalloadDeformationloadFrozen-heaveloadBlastingloadPre-stressBrakingload16.1Thermalload2Whentemperatureofsurroundingsofthestructuresischanged,thethermalexpansionofstructuresisrestrictedbytheboundarycondition.

Thermalstressisformedinstructuresandtheircomponents.

Thermaleffect,referstostructuredeformationandadditionalforcecausedbytemperaturechange.Thermaleffectdependsnotonlyonthetemperaturechangeofthestructureenvironment,italsorelatedtotheconstraintsofstructuralboundary.FoundationbeamFramedbentstructureBuildingroofMassconcrete6.1ThermalloadEnvironment

temperaturechangeStructureenvironmenttemperaturechangesAnnualtemperaturedifferenceMaxtemperature:JulyMintemperature:Janthe

middle

and

lower

reaches

of

Yangtze

river:annualtemperaturedifference:30℃NortheastChina:annualtemperaturedifference:60℃DifferenttemperatureinstructuresLocaltemperatureisdifferentinstructures.Reasons:sunshine,asuddencoldweather,etchightemperatureworkshop,coldstorageconditionsTemperaturechangeform6.1Thermalload4Consideringthedeformationcompatibility(結(jié)構(gòu)變形的協(xié)調(diào)性)UsingstructuralmechanicsandelasticmechanicsDeformationofatpointpalonganydirectionp-pCoefficientoflinearexpansion:lengthvariationwhentemperatureincreasesordecreasesonedegree.Temperaturevariationatthebaraxis軸TemperaturedifferencebetweenthetopandbottomSectionheightAreaoffigure：axisstressdistributionalongthebar.Areaoffigure:bendingmomentdistributionalongthebar6.1ThermalloadStructuraltypeSteelstructureRCStructureConcretemasonrystructureBrickstructurecoefficientoflinearexpansionα(10-6/°C）121097BeamBeamDisplacementcompatibilityconditionExample1:ElasticmodulusofthebeamSectionareaofthebeamThermalstress/Constraintstress6.1Thermalload軸Example2:FramedbentstructureLateralstiffnessHorizontalshearforce:CrosssectionalmomentofinertiaPillarheightBeamlength6.2DeformationloadDefinition:Foundationunevensettlement（不均勻性沉降）causedbyexternalfactorsofstructureStructureinternaldeformationandforcecausedbystructuralexpansionorshrinkagedeformation（結(jié)構(gòu)自身的膨脹或收縮引起的內(nèi)部變形與荷載）Sometypicaldeformationload:Bearing/supportmovementFoundationunevensettlementShrinkageandcreepofconcretestructureHyper-staticstructure6.2Deformationload偏移6.2Deformationload三門(mén)峽重力壩研究表明：溫度內(nèi)水壓力自重外水壓力三門(mén)峽重力壩三峽總公司副總經(jīng)理曹廣晶：溫度控制是三峽大壩混凝土質(zhì)量控制的重點(diǎn)和難點(diǎn),也是保證三峽大壩不出現(xiàn)危害性裂縫的關(guān)鍵。三峽大壩凝土裂縫（按照原因）1、大體積混凝土水化熱引起的裂縫2、塑性收縮引起的裂縫3、干縮引起的裂縫4、堿集料引起的裂縫5、溫度裂縫6、結(jié)構(gòu)基礎(chǔ)不均勻引起的裂縫7、鋼筋腐蝕引起的裂縫8、載荷引起的裂縫1、大體積混凝土水化熱引起的裂縫原因：水化熱，引起內(nèi)外溫度的急劇變化，形成溫度應(yīng)力。措施：分層、分塊、分縫冷卻（冷水管、預(yù)冷水)2、塑性收縮引起的裂縫原因：澆筑數(shù)小時(shí)后，混凝土處于塑性狀態(tài)，初凝表面水份蒸發(fā)過(guò)快，內(nèi)部水分補(bǔ)充不上，形成表面干縮。特點(diǎn)：裂縫可大可小，深度<5cm

不規(guī)則的網(wǎng)狀裂縫措施：覆蓋塑料布，防止水份蒸發(fā)過(guò)快增大環(huán)境濕度3、混凝土干縮引起的裂縫原因：硬化過(guò)程中，混凝土干縮引起體積變化，形成表面干縮。特點(diǎn)：裂縫寬與結(jié)構(gòu)的約束條件有關(guān)系

兩端固定、配筋梁、新老混凝土大壩基巖上澆筑混凝土措施：減少水泥用量、合理分縫、配筋

率降低4、堿集料引起的裂縫原因：堿集料反應(yīng)中生成的膨脹物導(dǎo)致混凝土開(kāi)裂。特點(diǎn)：平行于約束方向

網(wǎng)狀裂縫

收縮裂縫：垂直于約束方向5、溫度裂縫原因：大體積混凝土水化熱裂縫（特例）溫度變化，引起內(nèi)外變形不協(xié)調(diào)外

表面收縮裂縫海下儲(chǔ)油罐、混凝土煙囪、地下核反應(yīng)堆特點(diǎn)：平行于約束方向等間距、網(wǎng)狀裂縫措施：保溫措施、配筋、設(shè)置預(yù)裂縫

混凝土二維狀態(tài)下溫度破裂過(guò)程的數(shù)值模擬結(jié)果與試驗(yàn)結(jié)果

溫度引起混凝土路面翹曲過(guò)程的數(shù)值模擬

r3=100mmr3=105mmr3=110mmr3=125mm6、結(jié)構(gòu)基礎(chǔ)引起的裂縫原因：超靜定結(jié)構(gòu)受到不勻勻強(qiáng)迫變形作用使結(jié)構(gòu)破裂.1、土層均勻，但是由軟弱土層組成，引起沉降不均。6、結(jié)構(gòu)基礎(chǔ)引起的裂縫2.地基土層分布不均勻，且土的壓縮性有顯著差異時(shí)，有可能在房屋沉降曲線發(fā)生顯著變化處的相應(yīng)墻體上形成斜向裂縫。7、鋼筋腐蝕引起的裂縫原因：？？？特點(diǎn)：先銹后裂、沿筋破壞措施：？？？環(huán)境濕度保護(hù)層厚度裂縫情況混凝土的密實(shí)性抗碳化性能氯離子的含量8、載荷引起的裂縫原因：外界拉應(yīng)力>抗拉強(qiáng)度特點(diǎn)：與最大拉應(yīng)力正交措施：加筋、施加預(yù)應(yīng)力8、載荷引起的裂縫8、載荷引起的裂縫8、載荷引起的裂縫8、載荷引起的裂縫6.2Deformationload2008年11月15日杭州地鐵工地塌陷死亡11人6.2DeformationloadConcreteshrinkageload:Itisnotcausedbyexternalstress.Concretevolumeisdecreasedduetoitsshrinkage.MainReasons:ConcretehydrogelconsolidatesinhardeningprocessFreewaterevaporationinduceddryingshrinkageCracksareformedwhenshrinkagestressisconstrained.RoofcornercracksBeamcracksRoadcracks6.2DeformationloadInfluencefactorofconcreteshrinkagecrack:Concretestrengthgrade（強(qiáng)度等級(jí)）Aggregatetypes（集料類(lèi)型）Water-cementratioShrinkagecoefficientHowcanwedotopreventshrinkagecracks:expansionjointdistanceofthestructures;Setpost-pouringbelt（后澆帶）LocalreinforcedUseshrinkage-compensatingconcrete(收縮補(bǔ)償混凝土）6.2DeformationloadInfluencefactorofconcreteshrinkagecrack:ConcretestrengthgradeAggregatetypesWater-cementratioLargeshrinkagecoefficient:Highstrengthconcrete,ready-mixedconcrete,pumpingconcreteHowcanwedotopreventshrinkagecracks:Limittheexpansionjointdistanceofthestructures;Setpost-pouringbelt（后澆帶）LocalreinforcedUseshrinkage-compensatingconcrete(收縮補(bǔ)償混凝土）6.2DeformationloadConcretecreep:Definition:Concretedeformationincreaseswithtimewhenappliedconstantload.MainReasons:Smallload:Stressredistributioninun-crystallizedcementgel.Largeload:cracksinducedbystress.InfluenceofconcretecreepInstaticallydeterminatestructure,stressredistributionbetweenconcreteandreinforcingsteelwilleliminatestressconcentration.Instaticallyindeterminatestructure,theadditionalinternalforceinthemembersshouldberecalculated.6.2DeformationloadConcretecreep:CreepcoefficientRatioofultimatecreepstraintoinitialelasticstrainInfluencefactorsConcretestresslevelConcreteagewhenloadedWater-cementratio;Maincauses:Whenenvironmentaltemperaturedropstothefreezingtemperatureofsoilthatcontainswater,porewaterinthesoilfreezesintoice,andtheloosesoilparticlescementstogethertoformfrozensoil.Seasonalfrozensoilfoundationintheprocessoffreezingandmelting,tendstoproducefrozenheavingandmelting,excessivedeformationoffreezingleadtostructuredamageanddestruction.6.3Frozen-heaveloadFrozensoiltypes:permanentlyfrozensoilseasonalfrozensoil

instantaneousfrozensoilInfluencingfactor:FreezedegreeWatercontentSoiltypes（gravel<coarsesandsoil<finesandsoil<cohesivesoil\silt）Externalstresscondition(unfrozensoildeformation,loadsonfrozensoil)水平凍脹力切向和法向凍脹力Frozen-heaveloadtypes:Horizontalfrozen-heaveloadVerticalfrozen-heaveloadTangentialfrozen-heaveload6.3Frozen-heaveloadSlightfrozenMediumfrozenStrongfrozenSuperstrongfrozenClayandsilt30~6060~8080~120120~150Sand,gravel<1020~3040~8090~200Tangentialfrozen-heaveload（kPa/m2)Tangentialfrozen-heaveloadClaySandGravelsoilCoarsesandMeanload30412913458Maxload43037128178Horizontalfrozen-heaveload（kPa/m2)6.3Frozen-heaveload6.4ExplosiveblastingloadExplosionblastingload:InaveryshorttimesuddenlyAlargeamountofenergyreleasePhysicalorchemicalprocessApplyinghighpressureonthesurroundingsinwaveform

Accordingtothenatureofthemechanismandeffectofexplosion/blasting,theycanbedividedintothreemaintypes:physicalexplosion(boilerexplosion)chemicalexplosion(explosiveorgas)nuclearexplosion(nuclearfission-atomicandnuclearfusion-hydrogenbomb).

動(dòng)力作用下地下洞室圍巖動(dòng)態(tài)破壞規(guī)律地應(yīng)力大小:

初始地應(yīng)力越大，對(duì)圍巖裂紋擴(kuò)展長(zhǎng)度、速度的抑制性更強(qiáng)烈較低的靜應(yīng)力場(chǎng)中，動(dòng)態(tài)應(yīng)力波占主導(dǎo)地位pppp2p2p2p2p3p3p3p3p同一時(shí)刻不同地應(yīng)力狀態(tài)下的裂紋擴(kuò)展高頻應(yīng)力波AA'BB'K=0K=1pppppp

動(dòng)力作用下地下洞室圍巖動(dòng)態(tài)破壞規(guī)律6.4ExplosiveblastingloadRapidpressureboosting,andnegativepressurePressureboostingtimeNuclearexplosion：<10msChemicalexplosion：1~100msGasexplosion：100~300msNuclearexplosionChemicalexplosionGasexplosion6.4ExplosiveblastingloadShockWave(沖擊波）

Pressurebooststoreachitspeakvalueinashorttime,thesurroundinggasisrapidlycompressedtomoveinhigh-speed.

wavefrontier:

shockwavesurface（波陣面）-overpressure（超壓）,staticpressure

Afterwavefrontier:

dynamicpressure(relatedtoobjectshapeandorientation)Nuclearexplosion\chemicalexplosion:overpressure+dynamicpressureGasexplosion:overpressure1987年3月，哈爾濱亞麻廠粉塵爆炸亞洲最大的亞麻生產(chǎn)中心1.3萬(wàn)平方米的3個(gè)車(chē)間變成了一片廢墟58人死亡,100多人受傷6.4ExplosiveblastingloadIndustryworkshop,kitchen（泄爆保護(hù)）—:Roofisblownoffandwindowglassiscrushed.

Explosionventing(泄爆):reducetheexplosioneffectDragosavictheoryofgasexplosionpressurecurvemodel6.4Pre-stressPrestressedconcretestructuresTensilezoneCompressivezoneImproveconcreteanti-crackingperformance,stiffnessandstrength.ImprovestructuredurabilityReducestructureweightSavematerialsHighprice.Needspecialequipment,techniquesandmaterials.6.4Pre-stressPrestressedmethod:先張法(Pre-tensioningmethod)先張拉鋼筋后澆筑混凝土后張法(Post-tensioningmethod)先澆筑混凝土留孔道，后張拉鋼筋有粘結(jié)和無(wú)粘結(jié)有粘結(jié)：靠鋼筋與混凝土粘結(jié)而產(chǎn)生預(yù)拉力無(wú)粘結(jié)：靠錨具施加預(yù)拉力有粘結(jié)：先張后張無(wú)粘結(jié)：后張6.4Pre-stressPrestressedmethod:先張法(Pre-tensioningmethod)6.4Pre-stressPrestressedmethod:Post-tensioningmethod6.4Pre-stressExternalpre-stressing6.5BrakingloadVehiclebrakingforce:

Slidingfrictionbetweenwheelsandroadtoovercometheinertiaforce《公路橋涵設(shè)計(jì)通用規(guī)范》

Generalspecificationforhighwaybridgedesign(JTJ021—1989)Oneortwolanes:totalvehicleweightofonelane×10%

(notlessthan30%ofonevehicle)Fourlanes:

totalvehicleweightofonelane×20%Loadpoint:abovebridge/road1.2monthegravitydirection.6.5BrakingloadVehiclebraking force:

SlidingfrictionbetweenwheelsandroadtoovercometheinertiaforceVehiclebrakingforce(X):

Vehiclebrakingforce(Y):

10%ofthem