Rapid Damage Assessment Of Reinforced Concrete Columns After Explosion

Reinforced concrete columns are the key load-bearing elements of concrete structure.The damage and failure of reinforced concrete column under blast loads may further cause the progressive failure of the structure and aggravate the degree of disaster.Therefore,the damage assessment of reinforced concrete columns after explosion is of great significance for the performance evaluation of structures after disaster.As the determination of post disaster blast load is a difficult problem,the Pressure-Impulse(PI)diagrams method of damage assessment of reinforced concrete columns under blast loads is difficult to be applied to the post explosion damage assessment of reinforced concrete.In this paper,the damage identification method of structural members based on frequency change in the field of health monitoring is used for reference.The change rule of the first-order frequency of reinforced concrete columns before and after explosion is studied.The damage assessment index of reinforced concrete columns is established.A fast assessment method of reinforced concrete columns’ explosion damage based on the change of frequency measured in the field is proposed.The research work and achievements are as follows:(1)A numerical method for modal test of reinforced concrete columns is proposed.By applying impulse load instead of hammer force and directly extracting multi-point acceleration time history curve instead of acceleration sensor,the extracted force signal and acceleration signal are analyzed by frequency response function,and then the frequency and mode of reinforced concrete columns are obtained.(2)The change rule of the first-order frequency of reinforced concrete columns under blast loads is studied.The results show that the damage caused by the blast load will reduce the first-order frequency of reinforced concrete columns;the first-order frequency is not sensitive to the minor damage,but the first-order frequency changes obviously with the increase of the damage.(3)The damage index of reinforced concrete column based on the first-order frequency change is established.Through parameter studies,the influence rules of transverse reinforcement ratio,longitudinal reinforcement ratio and column aspect ratio on the frequency change of reinforced concrete column before and after blast loads are studied.The results show that with the change of physical parameters of reinforced concrete columns,the proposed damage index based on frequency change has a good correlation with the damage index based on vertical residual bearing capacity.(4)On the basis of parameter studies,the least square curve fitting method is used to get the suggested formula for rapid assessment of damage degree of reinforced concrete columns,so as to realize the rapid assessment of damage degree of reinforced concrete columns in the explosion site.