Study On Performance Of Concrete-Filled Steel Tubular Columns Under Combined Actions Of Fire And Impact Loadings

Concrete filled steel tubular(CFST)is a kind of composite structure formed by filling concrete in steel tube.It is widely applied in high-rise buildings,super high-rise buildings,subway station and other important structures,due to its advantages of high load-bearing capacity,good plasticity and ductility,convenience of construction and good fire resistance.Generally,CFST members are usually employed as the vertical bearing members of the important structures.Therefore,the buildings may be damaged or even collapsed when CFST fails.In recent years,with the increasing fire accidents and terrorist attacks,the mechanical properties of structural members subjected to multiple hazards(fire,impact,blast,etc.)have gradually attracted the social attention.Therefore,finite element(FE)models of CFST columns subjected to single fire,impact,blast and combined actions of fire,lateral impact and blast are developed.The mechanical properties of CFST subjected to multiple hazards are emphatically analyzed.The contents of this research are as follows:(1)The FE models of CFST members subjected to single fire,lateral impact and blast were developed.Considering that the model needs coupled temperature-displacement element to conduct the combined calculation of temperature and dynamic load,fire resistance models under ISO 834 fire condition were developed by the method of fully coupled thermal-stress.The effect of strain rate on the mechanical properties of materials was considered in the FE models of impact and blast,and the combined calculation of axial force and impact load was carried out.Based on the existing test results,the reliability of finite element model of CFST subjected to single hazard was verified.(2)The FE models of CFST columns under combined actions of fire and lateral impact were developed by using the coupled temperaturedisplacement step.The multi-hazard coupled models were verified based on the existing test results.The full-range analysis was carried out to investigate the mechanical properties of CFST subjected to combined actions of high temperature and impact through typical-members.The temperature field,mechanical properties under high temperature,failure mode,load and deformation,stress and strain development,interaction between steel tube and concrete and energy distribution between components were analyzed.Based on full-range analysis,the main parameters affecting the impact resistance of CFST members under elevated temperature were analyzed,including the fire duration,strength of concrete and steel,steel tube thickness,impact speed and impactor mass.(3)The FE models of CFST columns under combined actions of fire and blast load were developed.Then the full-range analysis was carried out to investigate the mechanical properties of CFST subjected to combined actions of high temperature and blast through typical-members.The deformation characteristics,failure mode,load and deformation,stress and strain development,interaction between steel tube and concrete and energy distribution between components were analyzed.The main parameters affecting the blast resistance of CFST members under elevated temperature were analyzed,including the fire duration,strength of concrete and steel,steel tube thickness and proportional distance.