Numerical Analysis Of Fire Resistance Performance Of Reinforced Concrete Columns After Earthquake

Fire is one of the most common and most harmful secondary disasters after an earthquake.As the earthquake will damage the building structure and its fire resistance performance will decrease at the same time,the casualties and property losses caused by the fire after the earthquake are often greater than the losses caused by the earthquake itself.Reinforced concrete column is an important supporting member in building frame structure.Scholars at home and abroad have studied more on its seismic performance and fire resistance,but relatively few studies on its fire resistance after earthquake.Accordingly,this paper takes the different degrees of damage of reinforced concrete columns after earthquakes as the "initial conditions",and uses the finite element software ABAQUS to study the fire resistance of reinforced concrete columns after earthquake damage.The main research contents and results are:(1)Firstly,the constitutive relationship between concrete and steel bar at room temperature under reciprocating load is selected,and the reliability of the material constitutive relationship,model parameters and finite element model is verified by comparing with the test results.Then a hysteretic model of reinforced concrete columns was established,and the hysteretic performance of reinforced concrete columns under various parameters such as axial compression ratio,reinforcement ratio,concrete strength,and strength grade of longitudinal reinforcement was analyzed.The results show that three factors such as axial compression ratio,reinforcement ratio and strength grade of longitudinal bars have a greater impact on the change of column hysteresis curve and ductility.As the axial compression ratio increases,the hysteresis area of the column becomes smaller and energy consumption The effect becomes worse.With the increase of the reinforcement ratio and the strength of the longitudinal reinforcement in the column,the hysteresis curve area of the column increases,and the ability to dissipate seismic energy increases;the reinforcement ratio of the column and the strength grade of the longitudinal reinforcement have an effect on the skeleton curve.The bearing capacity and ductility of reinforced concrete columns are directly proportional to the reinforcement ratio and the strength grade of the longitudinal reinforcement,but the higher the reinforcement ratio,the better;the axial compression ratio and the reinforcement ratio have an effect on the stiffness of the column The speed of degradation has a greater impact.Although the initial stiffness of a column with a relatively large axial compression is higher,as the loading progresses,its stiffness degradation rate is much greater than that of a column with a relatively small axial compression;increasing the reinforcement ratio of the column can be effective Improve the initial stiffness of the column and the rate of stiffness degradation,but the reinforcement ratio is not as large as possible.(2)The calculation methods of thermal properties and mechanical properties of concrete and steel bars at high temperature at home and abroad are summarized and analyzed,and the calculation methods of thermal properties and mechanical properties of concrete and steel bars in this article are reasonably selected.Through comparison with the test results,the selection of concrete and steel related parameters and the accuracy of the finite element model were verified,and then the temperature field and fire resistance limit analysis model of the reinforced concrete column was established,and the fire conditions and cross-section of the reinforced concrete column were analyzed.Temperature field under different parameters such as size and fire time,and fire resistance under different parameters such as axial compression ratio,reinforcement ratio,concrete strength,section size,load ratio,etc.The results show that:the fire conditions and fire time have a greater impact on the temperature field of the reinforced concrete column.When one side is exposed to fire and all four sides are exposed to fire,the temperature difference at the center of the concrete column at 180 minutes at high temperature is about 280℃,when all four sides are exposed to fire,the temperature difference of measuring point 1 and measuring point 2 inside the column is about 160℃ when the fire time is 140 min and 200 min respectively;the axial compression ratio,concrete strength and load ratio are compared with the steel bar The fire resistance limit of concrete columns has a greater influence.As the axial compression ratio and load ratio increase,the fire resistance limit of the column decreases.When the axial compression ratio is 0.2 and 0.8,the fire resistance limit of the column differs by about 100 minutes.When the load ratio is 0.15 and0.6,the fire resistance limit of the column differs by about 130 min.As the strength of the column concrete increases,the fire resistance limit of the column is extended.When the concrete strength is taken as C30 and C60,the fire resistance limit of the column differs by about 100 min.(3)Summarize and analyze the existing seismic damage model calculation formulas for reinforced concrete columns,reasonably select the seismic damage model calculation formulas in this paper,and then establish the fire resistance limit model of reinforced concrete seismic damaged columns,and analyze the damage degree,axial compression ratio,load ratio and The fire resistance limit of the seismically damaged column under various parameters such as fire time.The results show that the degree of damage,axial compression ratio and load ratio are the main factors affecting the fire resistance of seismically damaged columns.With the increase of the damage degree,axial compression ratio and load ratio,the column fire resistance limit gradually shortens.Compared with the undamaged column,when the damage degree is more serious,the column fire resistance limit differs by about 100 minutes.When the axial compression ratio is 0.2 and 0.8,the fire resistance limit of the column differs by about 55 min,when the load ratio is 0.15 and 0.6,the fire resistance limit of the column differs by about 95 min.