同济大学双语钢结构2-Structural-steel

BASICPRINCIPLESOFSTEELSTRUCTURESPhone:15800660849Preparedby:Dr.FengZHOURoom:Rui’anBuilding207A(welcometowalk-in)BASICPRINCIPLESOFSTEELSTRUCTURESTopic2StructuralsteelReviewoflastcoursemetallurgySteelfabricationMember+connectionstructuralsystemLoadsStrength,stability,rigidityForce,deformationS≤RPerformance:Safety,serviceability,durabilityMainfeatures:ApplicationsDesignconcept&rationaleStructuralsteelOutlinesrequirementsonmaterialpropertiesforstructuralsteelstateofstressandstressconcentrationductile,brittleandfatiguefailurefactorsaffectingsteelpropertiessteelgrade,steelselection&steelproductsrecentadvancesofstructuralsteelRequirementsonmaterialpropertiesHighstrength－highcapacitytoresistanyactingforcesEnoughdeformationability－ductility,toughnessGoodfabricationability－cold-formingability,weldabilityDurabilityinvariousenvironments－lowtemperaturecorrosivenessenvironmentrepeatloadReferto§2.1─§2.5Requirements:strengthandductilityuniaxialtensilecoupontest-preparationandtestingCouponspecimenSamplelocation:transverseorlongitudinalCouponspecimen:shapeanddimensionAsmallcouponofmaterialtakenfromthesteelispulledinatestingmachineuntilitfractures.NNNNReferto§2.1fyfufefpoTensilestrengthYieldstressProportionallimitsatga=E=2.06×10MPaYoung’sModulus5ElasticlimitsOAE－elasticrangeECF－plasticrangeFB－strainhardeningBD－neckingandfailureRequirements:strengthandductilitytensilecoupontestcurveStress-straindiagramfortypicalmildsteelPlasticrangeECFNonlinear,,obvioushorizontalyieldplateauLoweryieldpointistakenasyieldstress,fyElasticplastic,permanentstrainremainsaftertheloadisremovedElasticrangeOAELinearelasticandhook’slawworksσ=Ee,noresiduestrainremainsaftertheloadisremovedSmalldeformationsuperpositionprinciplecanbeused.oRequirements:strengthandductilitytensilecoupontestcurveNeckingandfailureBDThespecimenbeginsto“neckdown”asthestressesdecreasewithstainincreaseStrainhardeningFBAdditionalloadisrequiredtocauseadditionalelongationThemaximumstressiscalledtensilestrength,fufuRequirements:strengthandductilitytensilecoupontestcurve1.Yieldstress(fy)isusedinsteeldesign：（1）Elasticlimit(fe),proportionallimit(fp)andyieldpoint(fy)arecloseandcanbeassumedonlyonepointbetweenelasticandplastic（2）strainatdifferentrange?（3）yieldstrength,fu/fy,1.2….?2.Elastic-plasticmodelcanbeadoptedinsteeldesign.Elastic-plasticmodelPlastic,E＝0Elastic,E=206GPaofyfefpfuStress-straindiagramRequirements:strengthandductilityKeypointsonstrengthsest=10~15eyformildsteelorlow-alloysteel.Howabouttheultimatestraine5?Strain-hardeningstrainis10to15timesyieldstrainformildsteelorlow-alloysteel.Howabouttheultimatestrain?Nominalstress=conventionalstress=engineeringstressTruestressRequirements:ductilityelongation&reductionofareaductility:anextenttowhichamaterialcansustainplasticdeformationwithoutrupturepercentageelongationatfailure,d5(forl0/d0=5)percentagereductionofareatrueassessmentcriteriabutdifficulttomeasurethrough-thicknesspropertyRequirements:ductilityelongation&reductionofareaFunctionsofgoodductility:•toredistributethestress•toavoidbrittlefailureYieldstress(fy),yield-strengthratio(fu/fy)andelongation(d5)arethebasicmechanicpropertiesandmustbesatisfiedwiththerequirementsbythesteeldesignspecifications.Requirements:toughnessstatic&impactloadimpacttoughness(ak):anextendtowhichasteelabsorbsenergywithoutfracture.Expressedasenergyabsorbedbynotchedspecimeninanimpacttestak=Ak/An(Unit:J/cm2)Ak－workbyimpactloadAn－netareaatthenotch（a）CharpyVNotchImpacttest(CVN)VnotchImpactspecimenImpactloadRequirements:toughnessCharpyV-notchimpacttestToughnessisrelatedtoductilitybutdifferentfromductilityToughnessiscomprehensivereflectionofstrengthandductilityToughnesscouldbemeasuredusingtheareacoveredbystress-straindiagramToughnessistemperature-dependentRequirements:toughnessRequirements:cold-formingabilityCold-formingability:abilitytodeformplasticallywithoutfractureinaformingprocessunderroomtemperaturecomprehensivereflectionofsteelductility,qualityofsteelcrystalstructuremeasuredbycold-benttestCold-benttestBent180°nocrackordelaminationRequirements:WeldabilityWeldabilityreferstothecapacityofasteeltobeweldedintoasatisfactory,crack-free,soundjointunderfabricationconditionswithoutdifficulty.•Construction:nocrackinweldsundernormalweldingprocess•Usage:mechanicalpropertiesofweldsarenotlessthanthatofthebasemetalItisbasicallydeterminedbythechemicalcompositionofthesteelandvarieswithtypesofsteelandtheweldingprocessesused.The‘‘StructuralWelding’’providesweldingprocessesforshieldedmetalarcwelding(SMAW),gasmetalarcwelding(GMAW),fluxcoredarcwelding(FCAW),andsubmergedarcwelding(SAW).Requirements:durabilitycorrosionresistance30-40%demolishedCoating,paintingCorrosion-resiststeel:Cu-P-Ti-Re,e.g.09CuPCrNi,SAM400AWStainlesssteelfatigueresistance•Fatiguestrengthisimportantforsteelstructuralmemberssubjectedtovibratory,cyclical,orrepeatedloads.•ThebasicfatiguepropertyisthefatiguelimitobtainedfromtheS–Ndiagram(SbeingthemaximumstressandNbeingthenumberofcyclestofailure)whichisestablishedbytests.•Wewillta