Research On Behavior Of Concrete Filled Steel Tube Reinforced Concrete Plane Frames Subjected To Fire

Concrete filled steel tube reinforced concrete column-reinforced concrete beams(SRC beams)structure has been widely used in practical engineering.The mechanical properties of the concrete filled steel tubule reinforced composite column frame structure under the combined action of standard fire and load are studied in depth,which has important reference for the fire resistance design of the frame structure.In this paper,the fire resistances of the concrete filled steel tube reinforced concrete plane frame structures are mainly studied,and the following aspects are mainly carried out:(1)The experimental study on the fire resistance of four single storey single span square cross section concrete filled steel tube reinforced concrete column-reinforced concrete beam plane frame structure were carried out.The temperatures distribution,axial deformation of columns,deflection-time relation of beam,the failure mode and fire resistance were thoroughly studied.The effect of column fire load ratio,beam fire load ratio and beam column line stiffness ratio on the fire resistance of concrete filled steel tube reinforced concrete column plane structure was analyzed.(2)Based on the ABAQUS finite element analysis platform,reasonable selection the thermal parameters of steel and concrete material,a finite element temperature field model of concrete filled steel tube reinforced concrete column-reinforced concrete beam and concrete filled steel tube reinforced concrete column-steel reinforced concrete beam frame structure was established,and the calculation results were verified with the results of the related temperature field test and the temperature field test of the concrete filled steel tube frame structure.Based on the temperature field model of concrete filled steel tubular composite column frame,the temperature distribution of the frame structure was analyzed,and the factors affecting the temperature distribution of the frame structure were analyzed.(3)The mechanics model of steel and concrete material was selected correctly,and the mechanical model of concrete filled steel tubular reinforced concrete column-reinforced concrete beam and concrete filled steel tubular reinforced concrete column-steel reinforced concrete beam frame structure were established.The finite element model was proved with the experimental research on the fire performance of the CFST frame structure and the test results of the fire performance of the CFSTRC frame structure.The failure modes,joint stiffness,internal force,displacement of columns,deflection of frame beam,stress and strain development of concrete filled steel tube reinforced concrete column frame structure under fire were detailed analysed.(4)Influences of important parameters,such as column fire load ratio,beam fire load ratio,beam-column linear stiffness ratio,beam-column moment ratio,column slenderness ratio,column section size,column section core area ratio,steel yield strength,compressive strength of core concrete and compressive strength of concrete outside the column,fire resistance,internal change,the displacement of top column frame and deflection of frame beam of concrete filled steel tube reinforced concrete column-reinforced concrete beam under fire were analysed.A simplified formula for calculating the fire resistance of a single story single span square section concrete filled steel tubular reinforced concrete column-reinforced concrete beam was fitted,which can provide a reference for the fire resistance design of such structures.