Steel reinforced concrete(SRC)cross-shaped column is one of the main forms of SRC special-shaped columns.Compared with ordinary reinforced concrete columns,it has the advantages of strong bearing capacity,high rigidity,and flexible layout.It has been widely used in high-rise and super high-rise building structures.After the fire,the mechanical properties of the SRC cross-shaped column changed.In order to evaluate the loss of its mechanical properties for subsequent reinforcement and repair,the post-fire behavior of the SRC cross-shaped column has been simulated and analyzed.The contents and results are as follows:(1)In order to explore the performance of the SRC cross-shaped column after the fire,ABAQUS software was used to establish the heat transfer analysis model and structural analysis model by the thermal coupling method.According to the cross-section temperature distribution,time-temperature curve,failure mode,and load-displacement relationship of the cross column after the fire,the simulation results of the cross-shaped column were compared with the existing test results.The results show that the simulation results and the test results were anastomotic.(2)Sensitivity analysis was carried out on the simulation of the SRC cross-shaped column,in order to select the most suitable modeling conditions and provide a reference for the future SRC structure modeling.Sensitivity analysis includes thermal parameters of steel and concrete,mechanical properties of steel(yield strength,ultimate tensile strength,and elastic modulus),mechanical properties of concrete(compressive strength and elastic modulus),the stress-strain relationship of concrete,initial geometric defects,thermal expansion coefficients,and member element types.The results show that the finite element simulation of the cross-shaped column after the fire has a strong sensitivity to the selection of thermal parameters,mechanical properties,and the stress-strain relationship of concrete.(3)The residual bearing capacity coefficient was introduced,and the influence of key parameters on the residual bearing capacity and residual bearing capacity coefficient of the SRC cross-shaped column after the fire was discussed.Key parameters include constant temperature duration,maximum temperature,compressive strength of concrete,yield strength of section steel,yield strength of reinforcing bars,section edge length,calculated column length,bar diameter,steel ratio,eccentric distance,and load angle.The results show that the increase in constant temperature duration,maximum temperature,concrete compressive strength,and calculated column length can adversely affect the residual bearing capacity coefficient of the cross-shaped column.The yield strength of section steel,section side length,bar diameter,and steel ratio increase have a favorable effect on the residual bearing capacity factor of the cross-shaped column.Which was most sensitive to maximum temperature and the compressive strength of the concrete.In addition,within the set range,yield strength of reinforcing bars,eccentric distance,and load angle have little effect on the residual bearing capacity coefficient of the cross-shaped column,so were ignored in the following formula derivation.(4)The temperature calculation method of cross section measuring point and the simplified calculation method of residual bearing capacity of the cross-shaped column under axial load after the fire are proposed.By comparing the time-temperature relationship between the calculation results and the simulation results and the ultimate bearing capacity of the cross-shaped column after the fire,it can be shown that the calculation method is accurate.This method can provide a reference for the subsequent performance of steel-concrete composite structures after the fire.Finally,according to the proposed calculation method,a set of cases are designed for further discussion. |