Research On Fire Resistance Of Earthquake Damaged Reinforced Concrete Frames

Post-earthquake fire will seriously affect the local economy,causing casualties and collapse of buildings.Studies have shown that structural damage is caused by the fire after the earthquake rather than the earthquake itself in about 80% of the cases.In the field of structural engineering,there are few studies on the response of structural damage caused by fires following the earthquake and structural seismic design ignores the effect of post-earthquake fire on structure.As Reinforced concrete structure(RC structure)is the most widely used structure,finite element numerical simulation method in this paper is adopted to study the fire resistance of reinforced concrete structure after earthquake.The main work and results are as follows:(1)The thermal performance and mechanical properties of steel and concrete under high temperature are summarized.By comparing the four-sided fired reinforced concrete column finite element model calculation results of the temperature field and fire resistance endurance of the established by the finite element software ABAQUS with the existing test results,the reliability of the model is verified and a reasonable calculation model is selected for this paper;The temperature field influencing factors of reinforced concrete columns subjected to fire on four sides were studied,and the effects of reinforcement ratio,heating time,thickness of concrete cover,water content,section dimension and section geometry on temperature field of section were analyzed.The results show that the main factors affecting the temperature field of the section are heating time,thickness of the concrete cover and length of the section,while the heating time has the greatest influence on the temperature field of the column section.(2)The finite element simulation scheme of reinforced concrete structure under the action of earthquake fire is established,and the finite element calculation results of damage reinforced concrete column are compared with the existing test results to verify the rationality and applicability of the model;When subjected to fire on one,adjacent two,three and four sides,the temperature field distribution,failure mode,internal force variation and fire resistance of the damaged reinforced concrete column are studied,and Contrasting with reinforced concrete columns that only experience fire.the results show that the fire resistance of reinforced concrete columns is gradually reduced with the increase of the number of fire surfaces.The fire resistance of reinforced concrete columns subjected to seismic damage is lower than the fire resistance limit of columns only under fire.A method for evaluating the performance of RC components under earthquake-fire based on lateral displacement is proposed.(3)The finite element model of reinforced concrete single-layer frame structure with earthquake fire is established and the hysteresis curve analysis under earthquake and the temperature field analysis under fire are carried out to compare the finite element calculation results with the existing experimental research results;The internal force variation and deformation analysis of the reinforced concrete frame structure under the two different working conditions of fire effect and earthquake fire effect are compared;The fire resistance of reinforced concrete frame structures with different earthquake degrees is analyzed.The results show that internal force changes of seismic damage frame structures are more complicated under fire.As the temperature increases,the damaged frame moves from the position at the end of loading to the initial position,and the floor is the weaker structure in the fire.