Research On Fire Resistance Performance Of Fabricated Concrete-filled Steel Tube Frames

Because of its advantages in environmental protection,quality and safety control and optimization of building scheme,the fabricated structure has been widely used in the field of architecture in recent years.The assembled frame of concrete filled steel tubular column connected by single side Bolt has not only the advantages of high bearing capacity,good earthquake resistance and fire resistance of concrete filled steel tubular column,but also the characteristics of simple joint construction and quick construction.At present,there are some researches on the seismic behavior of concrete filled steel tubular(CFST)column singleside bolted joints and frames,but there are few reports on their mechanical behavior and failure mechanism at high temperature.In this paper,the fire resistance performance of four single-side bolt-connected concrete-filled circular steel tubular frames under ISO834 standard temperature condition is tested,and the main parameters affecting the fire resistance performance of the frames are analyzed:(1)taking steel ratio,load ratio and fire-retardant coating thickness as test parameters,the fire-resistant performance tests of two pieces of concrete-filled steel tubular(CFST)with unprotected and two pieces of extended end-plate connections with protected unilateral bolts were carried out.The temperature field,deformation curve,fire resistance limit and failure process of the frame are obtained.(2)the failure modes of the fabricated concrete filled circular steel tubular frame under fire are: end-plate yield joint,bending failure of steel beam and bending failure of concrete filled circular steel tubular column.The concrete filled circular steel tubular frame column without protection reaches the fire-resistant limit first,and the concrete filled circular steel tubular frame beam with protection reaches the fire-resistant limit first.The frame column experienced thermal expansion stage,steel pipe independent stress stage,material softening and common stress stage,specimen failure stage.(3)when the load ratio is constant and the steel ratio of column section is increased,the fire resistance of concrete filled circular steel tubular frame increases correspondingly.With the increase of the beam load ratio,the fire resistance of CFST frame decreases.The fire resistance of concrete filled circular steel tubular frame with protective layer is higher than that of the frame without protective layer.(4)the finite element analysis software ABAQUS is used to establish the fire performance analysis model of concrete filled circular steel tubular frame.Furthermore,the stress distribution and Development Law of the joint,as well as the failure mechanism of the frame are analyzed.(5)using the validated model,the influence of load ratio,steel ratio,end plate thickness,protective layer thickness and other parameters is analyzed.The results show that the fire resistance of the frame increases with the increase of load ratio,steel ratio and the thickness of protective layer.With the increase of end-plate thickness,the fire resistance of frame increases,but the increase is small.