Research On Behaviors And Design Methods Of Elliptical Concrete Filled Steel Tube Under Torsion,Shear Force And Local Compression

The elliptical concrete-filled steel tube(ECFST)is a n ovel type of concrete-filled steel tube composed of oval steel hollow section and core concrete.The ECFST has advantages of high loading capacity,favorable plastic property and easy construction,etc.In addition,the ECFST could reduce the flow resistance along its major axis.The cross-section slenderness of the ECFST could be adjusted according to different force condition.The ECFST is favored by scholars and architets,owing to a special aesthetic effect.The ECFST is gradually applicated to engineering example such as airport building,railway station,bridge pier and so on.However,studies on E CFST mainly focused on the bending performance,axial and eccentric compressive behavior,the research on t he ECFST under torsion,shear force and local compression is scare.Therefore,in order to study the mechanical property of the ECFST systematically,it is necessary to study the mechanical properties and design methods of ECFST under torsion,shear force and local compression.Two types of ECFST including oval-shaped elliptical concrete filled steel tube(OSECFST)and plane-shaped elliptical concrete filled steel tube(PSECFST)had been studied in this paper.The concrete works of this paper are as follows:(1)The numerical analysis model of two types ECFST members subjected to torsional load was carried out by ABAQUS software respectively.Geometric features,material nonlinearity and steel-concrete contact relationship were considered.The systematically parameter analysis of ECFST members was carried out,including steel and concrete strength,steel ratio,sectional area and cross-section slenderness.The failure modes and force mechanism of ECFST under torsion was investigated.(2)The numerical analysis model of two types ECFST members subjected to shear force was established on the long and short axis respectively through ABAQUS software.This thesis reveals the force mechanism and failure modes of the ECFST members in shear state,and focus on the parameters analysis on the shear behavior of the ECFST members.The parameters influencing the shear strength of ECFST members were analyzed on the long and short axis respectively,including shear span ratio,steel and concrete strength,steel ratio,cross-section slenderness and sectional area.(3)The numerical analysis model of two types ECFST members subjected to local compression was carried out by ABAQUS software respectively.The systematically parameter analysis of ECFST members under local compression was carried out,including steel and concrete strength,steel ratio,sectional area and cross-section slenderness.The failure modes and force mechanism of ECFST under local compression were revealed.(4)According to the parameters analysis and force mechanism studied in this paper,the design method of ECFST was deeply discussed on the basis of unified theory and superposition principle.The simplified calculation formulas of OSECFST and PSECFST under torsion,shear force and local compression was derived.It would be used as reference for finding design methods of ECFST.