| Elliptical concrete-filled steel tube(ECFST)is a new type of composite members,which can be divided into oval-shaped elliptical concrete-filled steel tube(OECFST)and round-ended elliptical concrete-filled steel tube(RECFST)according to sections.It not only has great architectural aesthetics in external appearance,but also can satisfy special stress state by distributing lateral stiffness of primary and secondary axes of structures reasonably,with flow resistance small as well.Therefore,they are gradually applied into factory buildings,public structures,bridges,airport terminals and other actual projects.However,researches on ECFST mainly focus on static properties at home and abroad at present,investigations on seismic performance of ECFST columns are mostly about circular,ectangular(square)and special-shaped CFST columns.Scarcely any studies on the seismic properties of ECFST have been reported,which limited the application of ECFST in actual projects severely.Accordingly,in order to study mechanical properties of ECFST systematically,it is necessary to conduct seismic performance experiments and discuss calculation methods towards oval-shaped and round-ended elliptical concrete-filled steel tube.This paper conducts horizontal low-cycle repetitive loading test on oval-shaped and round-ended ECFST columns by means of quasi-static experiments and numerical analysis methods.By analyzing test results under different parameters,doing relevant finite element analysis and calculating parameter,seismic property indexes are analyzed and the effects of various parameters on seismic properties and failure modes of ECFST columns are discussed.The main research work in this paper is as follows:(1)Oval-shaped and round-ended ECFST specimens were designed and made.By examining failure modes of specimens under horizontal low-cycle repetitive loads,load-displacement hysteresis curves,skeleton curves,ductility performance,strength degradation,stiffness degradation and energy dissipation of every specimen were analyzed.The effects of different axial compression ratio and concrete strength on the seismic performance of oval-shaped and round-ended ECFST were discussed at the same time.(2)Using finite element(FE)ABAQUS software,numerical analysis models of oval-shaped and round-ended elliptical concrete-filled steel tube columns were established applying equivalent stress-strain relationship for the core concrete.The accuracy of numerical analysis models was verified by comparing failure modes,hysteresis curves and skeleton curves of experiments and FE models.Nonlinear fullprocess analysis was also conducted towards typical oval-shaped and round-ended elliptical concrete-filled steel tube specimens.(3)The seismic properties of oval-shaped and round-ended ECFST columns offering different parameters were discussed systematically,including steel strength,concrete strength,axial compression ratio,slenderness ratio,diameter-thickness ratio,scale effect and loading direction etc,to research the influences of different parameters on the seismic properties of oval-shaped and round-ended elliptical concrete-filled steel tube.(4)On the basics of investigating seismic calculation method of oval-shaped and round-ended elliptical concrete-filled steel tube deeply,the simplified calculation method of hysteresis model and practical calculation formula of displacement ductility coefficient for the oval-shaped and round-ended ECFST were proposed on the basis of experiments and numerical analysis combining parametric analysis and force mechanism,which can be referred in practical projects. |
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