| Welding connections are extremely significant way to connect the steel structure.Not only welded steel structures are widely used in industry,aviation,spaceflight bridges,and so on,but it is widely utilized in the high-rise buildings as well because of its various advantages.However,it needs to be taken seriously that porosity,undercut and residual stress which stem from the welding process will directly affect the mechanical properties of the components and have an adverse effect on strength,deformation and whole stability.The welded beam-column connection in the high-rise steel structure under strong earthquakes is susceptible to brittle fracture and become the feeble part of whole structure,which may induce beam-column welded connection damage or entire structure collapse.Therefore,the fatigue properties of beam-column welded connection must be paid attention to.In this thesis,the topic of the fatigue deterioration mechanism and the fatigue life prediction methodology of beam-column welded connection in the high-rising steel structure were focused on and the following research has been performed by fatigue test,numerical simulation and theoretical analysis:In theory,the basic conception about the definition of fatigue,fatigue failure mechanisms and characteristics were expatiated in brief,research history and status quo,development trend were summarized in careful,and some factors affecting fatigue strength,some measures improving the fatigue strength,merits and demerits of the commonly used methods in estimating fatigue life were introduced in detail.On one hand,the low-cycle plastic-strain fatigue characteristics of standard welded seam specimen were carefully investigated by a serious of low-cycle fatigue test.On the base of test data,the cyclic stress-strain curve,hysteresis loop and the chief character of fatigue fracture was analyzed.The cyclic hardening rate decreased from 1.1 to 0.7 in the continuous and stable fatigue test.Subsequently,based on the fatigue test data and finite element analysis,a better formula for low cycle fatigue life prediction was derived by fitting the Manson-Coffin parameters.On the other hand,the elastoplastic dynamic response of high-rise steel structure under strong earthquakes was analyzed by SAP2000.The structural modal period ratio was 0.61 and the maximum elastic-plastic story drift ratios of structural X and Y direction was 1/110 and 1/125,which were considerably lower than standard limit of 1/50.Therefore,the strength,stiffness and stability of the high-rise steel structure conformed to the requirements of the steel structure design code.Then,most of the structural plastic hinges were found at the end of beams,which were in the LS(Life Safe)state.Next,beam-column welded connections that were prone to fatigue failure on the basis of the regularity of story drift ratios and structural damage were selected.Finally,the failure modes of beam-column welded connections were analyzed and some measures improving the fatigue performance were proposed.At last,the low cycle fatigue life prediction of beam-column welded connections selected was analyzed by ANSYS.Finite element analysis showed that the fatigue failure behavior of beam-column welded connections was consistent with the high-rise steel structure under actual earthquakes.By analyzing the stress nephogram and strain nephogram,the stress,strain regularity of welded connection were obtianed.Ultimately,the fatigue life of beam-column welded connections on the basis of steady local stress-strain method and the optimized fatigue life formula was predicted.The results obtained in this article give reference to the low cycle fatigue performance and fatigue life of beam-column welded connection of high-rise steel structures. |
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