| Elliptical concrete-filled steel tube(ECFST)is a new type of composite member with the advantages of both circular and rectangular composite sections.Because of its high bearing capacity,good seismic performance,small flow resistance and good aesthetic characteristics,it has been favored and concerned by the scientists and engineers and has been widely used in large bridge engineering,high-rise public buildings,long-span structure and large airport terminal building and other modern important livelihood projects.However,due to the construction technology,material characteristics and working environment and other factors,the interface between steel tube and concrete is separated,which seriously affects the bearing capacity,deformation capacity and ductility of members.Especially as the main stressed structures of public buildings,it may even cause great losses to national property and people’s personal health and property safety.At present,domestic and foreign scholars have conducted many studies on the initial defect between steel tube and core concrete,mainly focusing on the compressive performance of circular CFST columns,but the effects on compressive performance of ECFST columns has not been reported.Therefore,in order to popularize the application of elliptical CFST in practical engineering and clarify the influence of the gap imperfections on its mechanical performance,it is necessary to study the mechanical properties and the calculation method of bearing capacity of ECFST columns with gaps.In this paper,the eccentric compressive test was carried out for ECFST columns with a gap imperfection.Based on the actual engineering requirements,the eccentric compressive performance of ECFST short columns with different gap types was deeply studied.The specific research contents are as follows:(1)The eccentric compressive performance tests of 12 ECFST short columns with spherical-cap gaps were designed and conducted.The load-displacement curves,the longitudinal and transverse strain responses of the middle section,the strain distribution at characteristic points,the ductility and strength responses of the specimens were analyzed,and the typical failure modes and the mechanical properties of the ECFST short columns with spherical-cap gap were revealed.(2)Based on the experimental study,the core concrete constitutive of the ECFST with spherical-cap gap was modified,and the finite element analysis model of the ECFST short column with spherical-cap gap was established.The accuracy of the finite element model was verified by typical failure modes and load-displacement curves,and the effects of various parameters,such as gap ratio,eccentricity,steel strength,concrete strength,diameter-thickness ratio and long-short axial ratio on the specimen’s eccentric compression performance were investigated.(3)15 ECFST short columns with circumferential gap were tested.The load-displacement curve,the ultimate bearing capacity of the specimens,oval cross section in the longitudinal strain of steel tube and link to the strain development was analyzed.The performance of ductility and strength of the specimens were analyzed and explored the different loading direction,eccentricity,gap ratio and steel strength on ECFST short columns,especially for the eccentric compression performance and the influence of failure mode.(4)A finite element analysis model of an ECFST column with circumferential gap was established based on the response of steel-concrete interface with tests.The accuracy of the model was verified according to the test results and failure modes.A variety of dimensional and material parameters were analyzed.Combined with the contact stress,axial stress of the core concrete and axial stress of the outer steel tube,the whole process response of the specimen with long axial bias and short axial bias of the elliptical concrete filled steel tube with the circumferential gap was revealed.(5)Based on the experimental study of ECFST column with gaps,the finite element analysis and the two different gap types of ECFST short column of eccentric compression theory analysis,combined with the existing specifications and design methods of research,puts forward the calculation method of two types of ECFST short columns under the eccentric compression.The applicable scope of the formula is proposed,which can be used for reference in practical engineering. |
