Fire Performance Of Concrete Filled Steel Tubular Column-wall Structures

Concrete-filled steel tubular column-wall(CFST column-wall)is a new type of concrete-steel composite structure.It’s an assembly of several single U-shaped steel tube welded together,with concrete poured inside.It functions as both load-bearing column and shear wall in a structure.Existing design codes do not cover any specific provisions on the fire design of CFST column-wall structure.Therefore,it is of essential importance to investigate the fire performance of this kind of structure.This dissertation carried out a series of studies on typical CFST column-wall both experimentally and theoretically.Investigations were made on its thermal and structural mechanism in the combined full-range loading and fire process,as well as the fire design of CFST column-wall.The research work includes:1.Full-scale tests were conducted on CFST column-wall subjected to combined loading and fire.The test parameters include load ratio,insulation materials and thicknesses.Investigation focused on temperature to time relations,axial deformation,and fire resistance as well as failure modes of CFST column-wall under both loading and ISO-834 standard fire.2.A finite element analysis(FEA)model was established in order to simulate the thermal and structural behavior of CFST column-wall under both loading and fire.Based on relative existing models of conventional CFST columns,modifications were made in terms of thermal property models,constitutive relationship and interface behavior.Sensitivity studies were carried out to evaluate the influence of some factors such as water vaporization,interface gap,spalling of the insulation layer,initial imperfection and so on.The FEA model was verified against test data and turned out to be reasonably accurate in predicting the fire behavior of CFST column-walls.3.The verified FEA model was used to investigate the full-range analytical behavior of CFST column-wall.Heat transfer mechanism was analysed by comparing the temperature distributions of CFST column-wall sections with different fire exposures,and by investigating the insulation behavior of CFST column-wall with various wall thicknesses.Structural analysis,such as axial and lateral deformation,internal force distribution,strain and stress of different components,interface behavior between steel and concrete was given to describe the deformation behavior and failure mechanism of CFST column-wall.The influences of geometric nonlinearity and material nonlinearity on t he failure of CFST column-wall were discussed.4.On the basis of the FEA model and the full-range analysis,parametric analysis was carried out to investigate the influences of various parameters on the fire performance of CFST column-wall.The parameters include section perimeter,slenderness ratio,load ratio,aspect ratio,steel ratio,material strength,as well as the material type and thickness of the insulation layer.Based on the analytical results,a simplified calculation method was proposed to estimate the fire resistance of CFST column-wall structure,as well as the thickness of insulation layers.