Research On Related Problems Of Fire-Resistant Steel-concrete Composite Beams And Concrete Filled Steel Tubular Columns

Domestic and foreign scholars have conducted a large number of experimental and theoretical research on the fire resistance of steel-concrete composite beams(SCCB)since the 1990s,while the steel was usually conventional structural steel.Some scholars also analyzed the fire resistance behavior of fire-resistant(FR)steel members and steel-concrete filled steel tubular columns.Fire resistance of FR-SCCB has been little studied.This paper analyzed the fire performance of FR-SCCB and the main works and results are as follows:Fire-resistant tests were carried out to study the fire performance of FR-SCCB under standard fire.Two types of specimens were tested.One was conventional structural steel-concrete composite beam(CSSCCB),and the other was FR-SCCB with different thickness of fireproof coating.The test results show that the simply supported FR-SCCB reaches its fire limit state when the mid-span deflection reaches 1/30 of the span.FR-steel can be used to improve the fire resistance performance of steel-concrete composite beams and to decrease the thickness of fire-proof coating.The fire-resistance of fire-resistant steel-concrete composite beams(FR-SCCB)with fireproof coating and fire-proof board under standard fire were studied by using the finite element software ABAQUS.The effects of the load-ratio,fire-insulation of the steel beam,the strength of materials,the section size,and the diameter of longitudinal reinforcements in the concrete slab on the fire performance of FRSCCB were investigated.It is shown that load-ratio and fire-insulation thickness of the steel beam are the two most important factors that affect the fire resistance of FRSCCB.It has been found that the fire-resistance limitation will increase by over 35%when FRSCCB is used,and the fire-insulation thickness could be decrease by 30%.Also,the simplified calculation method according to Chinese code(CECS200:2006)for predicting the fire resistance limit is found to be conservative when the load ratio is small.Based on the high-temperature mechanical properties of the Q345 FR-steel,produced by the Wuyang Iron and Steel Co.Ltd,the fire performance of FR-SCCB is analyzed.The simulation results include both steady state and transient state.And the fire resistance time and the bending bearing capacity of FR-SCCB were acquired.The effects of the section size,the load-ratio,the fire-insulation thickness of the steel beam on both the fire resistance time and the bending bearing capacity were investigated.The simplified calculation formulas for predicting the bending bearing capacity and the fire resistance time were deduced,which are in good agreement with the FEM results.The bending bearing capacity results of the FEM methods were compared with the results of Chinese code CECS200:2006.The code method is found to be over conservative when the fire duration time was long.An improved computational method of the bending bearing capacity of FR-SCCB in fire was presented.Fire resistance of FR-SCCB exposed to fire on one face is analyzed,and the parameter analysis of the related factors was performed.The results show that the effects of the influencing factors on the fire performance of FR-SCCB exposed to fire on one face were similar to that of FR-SCCB exposed to fire on three faces.Also the fire resistance of FR-SCCB exposed to fire on one face was compared with that exposed to fire on three faces,and it indicated that the fire resistance limit time could be doubled.Fire resistance of FR-SCCB is the main research content in this paper.The other content is about some fundamental research on the performance of rectangular concrete filled steel tubular members.The details are as follows:Tests of four groups of rectangular concrete filled steel tubular members were carried out.The effect of width-to-thickness ratio on the post buckling bearing capacity of the CFRST column under axial compression was studied based on the experimental results.Parameter analysis was performed by using the verified finite element method.The results show that the width-to-thickness ratio has a great impact on the residual bearing capacity of the CFRST column under axial compression.When the width-to-thickness ratio is 60?,the residual bearing capacity of the CFRST short column might be down to 65%of the ultimate bearing capacity.For those concrete filled steel tubular columns,whose seismic capacity are govern by axial bearing capacity(such as the chord column of vertical bracing),the width-to-thickness ratio limit values should be stricter to 50?.Meanwhile,the confinement coefficient should not be less than a certain limit.