四川交通職業(yè)技術(shù)學(xué)院SichuanVocational&TechnicalCollegeofCommunications土木工程英語四川交通職業(yè)技術(shù)學(xué)院教學(xué)課件(The2ndTalent-CompetitionforTeachersofSVTCC)國家示范性高等職業(yè)技術(shù)學(xué)院教師：黃蜀云公共課教學(xué)nit6Stress&Deformation

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Stressisthephysicalpressureorotherforcesexertedonanobject.Deformationinanydirectionisthetotalchangeinthedimensionofamemberinthatdirection.DeformationForce

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pre-stressingoperatingWorkplatformAnchorboltsrebarconcrete

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A:Sincemanypre-stressingreinforcedconcretecomponentsareadoptedinproject,itisnecessarytohavealookatthepre-stressingoperating.fixingformworkexertingtension

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B:Therebarispre-stressedfirstbyacertaintensionforceandfixedonbothends.Thenwefixtheformworkandnon-prestressedrebar,andthenpourconcrete.Aftertheconcretereachesthedesignedstrength,thepre-stressedrebarare

released.pouringconcretereleasingrebar

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B:Therebarispre-stressedfirstbyacertaintensionforceandfixedonbothends.Thenwefixtheformworkandnon-prestressedrebar,andthenpourconcrete.Aftertheconcretereachesthedesignedstrength,thepre-stressedrebarare

released.releasingrebarpouringconcrete

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A:Thestrengthfromthepre-stressingmembersistransferredtotheconcrete,isn’tit?B:Yes.Thepre-stressedconcretewilloffsetsomeorallthetensionforcewhenitisunderthesituationoftensionstrength.rebaroffsetthetensionforce

Pressure

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A:Arethereanydifferencesbetweenthepre-stressedconcreteandnon-prestressedconcreteinconcretepouring?B:Inordertoreducetheconcreteshrinkageunderthepre-stressing,thepre-stressedconcreteshouldbepouredcontinuouslyinonetimewithoutconstructionjoints.theratioofwaterandcementshouldbelowandtheaggregateshouldbeselectedinbetterquality.constructionjoints

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A:Whencanthefixturesofthepre–stressedrebarberemoved?B:Itdependsonwhethertheconcretestrengthreachesthedesignedvalueornot.Atleastthetestshouldshowthattheresultisuptothestandard.ifthefixturearereleasedtooearly,itwillcauselotsofstrengthlossandevenseriousqualityproblem.

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TechnicalTermsoftheDialogue1.模板2.水泥3.骨料4.鋼筋混凝土5.預(yù)應(yīng)力6.預(yù)應(yīng)力鋼筋

7.施工縫8.拉(張)力

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GroupWorkTrytoexplaininyourownwordsthetechnicaltermslearnedinthedialogueandthentalkabouttheprocessofpre-stressingoperation.

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Whendesigningastructure,thedesignermustestimatealltheforcesactingonthestructureanditscomponentparts.Theeffectsoftheforcesarethenconsideredinrelationtothestabilityofabuildingasawholeandcomponentpartsaremadestrongenoughtocarrytheirparticularfunction.

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Theforcestobeconsidereddependonthetypeandpurposeofthestructure.Inbuildings,forexample,theforceswillbe

duetotheweightofthestructureanditsoccupantsaswellastothepressureexertedbywind.

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Theloadsofabuilding

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Inthewallforretainingearth,theforceswillbeduetotheweightofthewall,thepressureexertedonthewallbytheearthbehindit,andthepressureduetoanybuildingsorroadwaysnearthetopofthewall.擋土墻受力

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Theinternalfibersorparticlesofthevariouspartsofastructureareputintoastateofstressbytheforcestheyareneededtoresist,thebasicformsofstressbeingtension,compression,shearandtorsion.batensioncompression

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Intension,thematerialispulledapartorstretchedlikearubberband.

Incompression,thematerialispressedorpushedtogether.

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Whatistorsion?Itmakesthestructurerotateorturn.torsion

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Theshearingforcecausesshearingstress.Itisdefinedasthefractureofthematerialsalongthestressroute.shearFF

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Sincethestructuredesignedbycivilengineersisintendedtobestable,theseforcesmustbekeptinbalance.Theverticalforces,forexample,mustbeequaltoeachother.ifabeamsupportsaloadabove,thebeamitselfmusthavesufficientstrengthtocounterbalancethatweight.F1F2F1F2=

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Thehorizontalforcesmustalsobeequaltoeachothersothatthereisnottoomuchthrusteithertotherightortotheleft.theforcesthatmightpullthestructurearoundmustbecounterbalancedwithforcesthatpullintheoppositedirection.F1F2=F2F1

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ifamancarriesaheavyload,hisbodyisdistressedasa

resultoftheeffortshehastomaketobeartheload.Inordertograsptheideaofstress,itishelpfultocomparefibersofamaterialsubjectedtoforcetothebonesandmusclesofaman.

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Amaterialissuretodeformtoagreaterorlesserextentwhenitissubjectedtostress,althoughthedimensionalvariationsinstructuralmaterialsareusuallyveryslight.thedeformationproducedisoftencalledstrain.amemberstressedincompressionbecomesshorterandfatter.

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QuestionsWhatshouldadesignerestimateindesigningastructureWhatarethefourbasicformsofstress?Howcantheforcesofthestructurebekeptinbalance?Inwhatconditiondoesamaterialdeform?Takeanexample

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