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三門峽重力壩研究表明：溫度內(nèi)水壓力自重外水壓力三門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)量控制的重點和難點,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，形成溫度應力。措施：分層、分塊、分縫冷卻（冷水管、預冷水)2、塑性收縮引起的裂縫原因：澆筑數(shù)小時后，混凝土處于塑性狀態(tài)，初凝表面水份蒸發(fā)過快，內(nèi)部水分補充不上，形成表面干縮。特點：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)過快增大環(huán)境濕度3、混凝土干縮引起的裂縫原因：硬化過程中，混凝土干縮引起體積變化，形成表面干縮。特點：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：堿集料反應中生成的膨脹物導致混凝土開裂。特點：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油罐、混凝土煙囪、地下核反應堆特點：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)置預裂縫

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

溫度引起混凝土路面翹曲過程的數(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，有可能在房屋沉降曲線發(fā)生顯著變化處的相應墻體上形成斜向裂縫。7、鋼筋腐蝕引起的裂縫原因：？？？特點：先銹后裂、沿筋破壞措施：？？？環(huán)境濕度保護層厚度裂縫情況混凝土的密實性抗碳化性能氯離子的含量8、載荷引起的裂縫原因：外界拉應力>抗拉強度特點：與最大拉應力正交措施：加筋、施加預應力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（強度等級）Aggregatetypes（集料類型）Water-cementratioShrinkagecoefficientHowcanwedotopreventshrinkagecracks:expansionjointdistanceofthestructures;Setpost-pouringbelt（后澆帶）LocalreinforcedUseshrinkage-compensatingconcrete(收縮補償混凝土）6.2DeformationloadInfluencefactorofconcreteshrinkagecrack:ConcretestrengthgradeAggregatetypesWater-cementratioLargeshrinkagecoefficient:Highstrengthconcrete,ready-mixedconcrete,pumpingconcreteHowcanwedotopreventshrinkagecracks:Limittheexpansionjointdistanceofthestructures;Setpost-pouringbelt（后澆帶）LocalreinforcedUseshrinkage-compensatingconcrete(收縮補償混凝土）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).

動力作用下地下洞室圍巖動態(tài)破壞規(guī)律地應力大小:

初始地應力越大，對圍巖裂紋擴展長度、速度的抑制性更強烈較低的靜應力場中，動態(tài)應力波占主導地位pppp2p2p2p2p3p3p3p3p同一時刻不同地應力狀態(tài)下的裂紋擴展高頻應力波AA'BB'K=0K=1pppppp

動力作用下地下洞室圍巖動態(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1.3萬平方米的3個車間變成了一片廢墟58人死亡,100多人受傷6.4ExplosiveblastingloadIndustryworkshop,kitchen（泄爆保護）—: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)和無粘結(jié)有粘結(jié)：靠鋼筋與混凝土粘結(jié)而產(chǎn)生預拉力無粘結(jié)：靠錨具施加預拉力有粘結(jié)：先張后張無粘結(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