Numerical Analysis On Fire Resistance Of The Composite Connections After Earthquake Damage

Fire refers to the disaster caused by the loss of control in time or space.It is also one of the most common and destructive secondary disasters in various disasters after the earthquake.Most areas in China are located in earthquake zone.Since ancient times,it has been a country with severe earthquake disasters.After the earthquake,the structure will produce different degrees of damage,such as structural plastic deformation,material performance degradation,etc.accompanied by a series of secondary disasters,and secondary fires pose the most serious threat to the structure,which will aggravate structural damage.The speed even causes the structure to collapse continuously;the node acts as the most critical part of the structure,connecting the vertical and horizontal force members and transmitting all the loads.In recent years,the extensive application of combined joints in practical engineering is inseparable from its superior mechanical properties.Many scholars have conducted in-depth research on concrete-filled steel tubular members and structures under seismic and fire-resistant performances.However,the research on the fire resistance performance of such joints after seismic damage is relatively lacking.In this paper,the numerical analysis method is mainly used to study the fire resistance of concrete-filled steel tubular joints after earthquake damage by using the finite element software ABAQUS,including the following contents:(1)Research on seismic performance of CFST composite jointsThe premise of considering the material damage under the action of reciprocating load,the constitutive relation of steel and concrete under the action of reciprocating load is reasonably selected.The finite element software ABAQUS is used to verify the existing composite component and node hysteresis test.The rationality and correctness of the modeling method.On this basis,the whole process of concrete-filled steel tubular joints under cyclic loading is studied by typical examples.The effects of parameters such as axial compression ratio and beam-to-column stiffness ratio on the mechanical properties of the joint under cyclic loading are analyzed.(2)Research on fire-resistance performance of CFST composite jointsBased on the reasonable consideration of the thermal parameters of steel and concrete and the model under high temperature,the sequential thermal coupling method is used,the finite element analysis software ABAQUS is used to build the existing concrete-filled steel tubular members in different section types,steel joints,steel-reinforced concrete joints,concrete-filled steel tubular joints were numerically simulated and compared with the test.Based on the rationality of the verification model,the temperature transfer of the CFST composite joints under two different fire conditions was carried out by typical examples.The mechanical properties and failure modes under fire were analyzed,and the factors affecting the fire endurance of such joints were further studied.(3)Research on CFST composite joints subjected to post-earthquake fireThe damage index is used as the basis for determining the seismic damage of concretefilled steel tubular joints.The low-cycle reciprocating loading method is used to simulate the seismic action.By selecting the seismic damage index reasonably,the finite element model of the joint under different conditions is established.In the actual project,the characteristics of the fire are mainly caused by the following two types of fire conditions.For steel beam nodes,the lower column of the one node of the working condition is exposed to fire,and the rest is not affected by fire;the lower column and steel of the two nodes of the working condition The lower flange and web of the beam are exposed to fire,and the rest are not affected by fire.For composite beam nodes,the working condition is also that the lower column of the node is individually fired: the second condition is that the bottom part of the concrete slab is exposed to fire.The damage accumulation,temperature transfer and damage index of the joint after the damage are analyzed,and the influence of the fire mode on the fire endurance and failure mode of the joint is analyzed.