Study On Hysteretic Behavior Of T - Type Round Steel Pipe Joints After Fire

Circular steel tubular structures are attractive to architects due to their good mechanicalproperties, beautiful shapes and fast construction, and have been widely used in ocean platform, bigspanbridge,stadium,towerandsoon.Recently,moreandmorecircularsteeltubularstructureshavebeenthreatenedbyfirebecauseofthesensibilityofthesteelmaterialtohightemperature.Therefore,it isnecessary tostudy theperformanceof steel tubularstructures after exposure tofire. Meanwhile,it is also significant to study the aseismic performance of welding circular steel tubular structuresunder the loading of wave, earthquake and wind after exposure to fire. Based on the aboveintroduction, the experiment test and finite element analysis are carried out to investigate thehystereticbehaviorofcircularsteeltubularT-jointsafterexposuretofire.Theprincipalresearchcontentsarelistedasfollows,(1) Experiment tests are conducted to study the hysteretic performance of circular hollowsection (CHS) T-joints at ambient temperature and after post-fire respectively. The highesttemperaturethatCHST-jointsexperienceis500oC.Duringtheheatingenvironment,aconstantaxialloadingisappliedattheendofthebrace.ThetypicalfailuremodesoftheCHST-jointssubjectedtocyclic loadings under different conditions are observed. Compared the hysteretic curves, skeletoncurves, ductility curves, accumulative energy dissipation, strength and rigidity degradation of thespecimens, the effects of the high temperature on the hysteretic behavior of the CHS T-joints areanalyzed.(2)Thecorrespondingfiniteelement(FE)modelisbuiltbyusingtheFEsoftwareABAQUStoinvestigate the hysteretic behavior of the CHS T-joints at ambient temperature and after post-firerespectively. To make sure the accuracy of the FE model, many factors such as the dimension,boundaryconditionsandtheloadingprocessareassimilaraspossiblewiththeexperimentaltests.Inaddition,theeffectofweldingisalsotakenintoaccount.ItisfoundthattheresultsobtainedfromtheFEmodelsagree wellwith theexperimental results, which shows thereliability and accuracy oftheFEmodel.(3) Based on the verified model, parametric analysis is carried out to investigate the hystereticbehavior of the CHS T-joints after exposure to the fire. A bilinear kinematic hardening material model is adopted and the stress-strain relationship of steel after exposure to the fire is selectedaccordingtothedefinitioninrelativepublishedreference.Theeffectsofgeometricparametersα,β,γandthehistorytemperatureparametertonthehystereticbehavioroftheCHST-jointsafterexposureto the fire are discussed. The results show that the hysteretic behavior of the CHS T-joints afterexposure to the fire decreases slightly. With the increase of α and γ, the accumulative energydissipation ratio of the CHS T-joints decreases observably. While With the increase of β, theaccumulativeenergydissipationratiooftheCHST-jointsdecreasesfirstlyandthenincreases.