Study On Fire Resistance Of Seismic Damaged Reinforced Concrete Frame Structure

Earthquake secondary fires have the characteristics of high probability of occurrence,strong damage of disasters,huge losses and complicated mechanisms.Reinforced concrete frame structure is one of the main structural forms of our country’s buildings,and the structural bearing capacity under fire is significantly reduced,which leads to the collapse of local and even the overall structure.Therefore,it is necessary to study the post-earthquake fire resistance of the frame structure under the action of secondary fire.In this paper,a combination of theoretical analysis,experimental research,and numerical simulation is used to take the reinforced concrete frame structure at the middle damage level of the 8-degree fortification zone as the research object,reveal the high-temperature damage mechanism of reinforced concrete materials and components,and establish the fire resistance and high temperature bearing capacity of seismically damaged reinforced concrete frame structure.The research results have important reference for improving the fire resistance design of concrete frame structure and improving the disaster resistance of concrete structure.The main contents of this article include:(1)Based on the analysis and summary the existing seismic damage data and seismic test records,the concrete peeling and residual deformation are taken as the main seismic damage forms of the concrete structure.The distribution range of the damage is determined by means of data statistics and regression analysis,and then,the model of seismic damage concrete frame is established.(2)The temperature field calculation model and mechanical analysis calculation model of seismic damaged concrete columns are established by ABAQUS finite element software,and compared with the results of full-scale seismic damaged reinforced concrete columns’ fire-resistant performance test,which verifies the correctness of modeling process and parameters.(3)In this paper,the fire-resistant performance of two-story two span reinforced concrete plane frame structure is studied,and the finite element model of earthquake damaged plane frame structure is established by using ABAQUS finite element software.The influence of fire location,axial compression ratio,inter story displacement angle and relative spalling length on the distribution of temperature field,failure mode,deformation law,internal force change and fire resistance limit of plane frame structure is analyzed.The results show that the axial compression ratio and the story displacement angle have significant influence on the fire resistance of the plane frame structure,and the fire resistance reduction rate of the frame structure under the medium failure level is 0.69%-47.87%.(4)The fire resistance of reinforced concrete space frame structure under the action of two-way horizontal lateral displacement is studied.Based on the analysis of the calculation results of temperature field distribution,deformation rule and fire resistance limit,it is found that when the axial compression ratio is 0.63,the fire resistance reduction rate of the space frame structure under the medium failure level is13.33%-57.31%.(5)Four typical damaged concrete column models are selected to study the fire resistance performance,and the temperature field distribution of the cross section and the temperature rise curve of the measuring point are obtained.Based on the results of temperature field calculation,the high temperature bearing capacity and the reduction coefficient of high temperature bearing capacity are calculated,and the effects of fire time and relative spalling length on the bearing capacity of earthquake damaged concrete columns are studied.The quantitative relationship between the reduction coefficient of section bearing capacity and the relative spalling length and the time of fire is proposed.