Behaviour Of Concrete-filled Double-skin Steel Tubular Members Subjected To Impact After Exposure To Fire

Concrete-filled double-skin steel tube(CFDST)is a new kind of composite structural member which is formed by filling concrete between inner and outer steel tubes.It shows good performance in mechanical capacity and ductility and has a great prospect when applied in building,bridge and underground engineering.Fire is one of the main disasters of engineering structure.Mechanical properties of structures after fire provide an important basis for post-fire structural repair and reinforcement.This paper conducts the study of the behaviour of CFDST member under lateral impact load after exposure to fire.The main contents are listed as follows:1)The temperature field experiment and subsequent impact test are carried out for 15 CFDST members and 13 Concrete-filled steel tubular(CFST)members.The timehistory curves of temperature are recorded in the temperature field experiment.The failure modes of specimens,as well as the time-history curves of impact force,deformation,axial load and longitudinal strain are obtained in the impact test.The influence of different parameters on the impact resistance of CFDST and CFST members is also analyzed.2)The finite element(FE)model of the CFDST member is established.The constitutive model at different stages of fire,strain rate effect and interface contact relationship of steel and concrete are considered in the model.The coupled tempdisplacement elements are used to calculate the stress and temperature fields of specimen under fire.The accuracy of the FE model is verified by the test results.3)The verified FE model is used to analyze the post-fire failure mechanism of the typical CFDST member,which is designed based on common parameters in practical engineering.The stress distribution,impact failure mode,relationship of impact force and deformation,energy consumption,contact stress of interface and bending moment are discussed.In addition,the impact responses of specimens experiencing different timetemperature-load paths and specimen under room temperature are compared.4)The main parameters affecting the lateral impact resistance of CFDST member after fire are analyzed,including the impact energy,impact momentum,axial load level,fire duration,diameter to thickness ratio of the outer tube,hollow section ratio,yield strength of inner and outer tubes and compressive strength of concrete.