Dynamic Response And Damage Assessment Of CFST Columns Subjected To Blast Loading

With the change of terrorist target and the increase of gas explosion accidents, it becomes very essential to consider the blast load in the design of civil construction. The uses of materials or structures with superior antiknock performance are the most effective and economic way to resist blast load. Aiming at the concrete-filled steel tube(CFST) columns, which have high bearing capacity, outstanding plasticity and good durability, this dissertation studied the performance of CFST columns subjected to blast loading mainly from the following aspects: the generation and propagation of explosion shock wave, the dynamic behavior of materials, the dynamic response and damage evaluation of CFST columns. The main research contents and results are as follows:(1) The generation and propagation of the blast wave was simulated by numerical method. The effects of mesh sizes on the peak of blast wave、the applicability of the explosion similarity law and the influence of the rigid ground to the blast wave propagation were analyzed. The results can provide some basises for the simulation: the influence of the mesh size to simulation results decreases with the increase of distance; the explosion similarity law is not suitable when the reduced scale and the distance are small; the peak of the blast wave greatly increases when considering the reflection of the rigid ground, but the enhancement effect can be ignored when the distance of the explosive to the ground increases to a certain value.(2) The dynamic behaviors of concrete, steel and CFST were studied by the numerical models of Split Hopkinson Pressure Bar(SHPB), and the influences of parameter values(HJC model) to the numerical simulation results were analyzed. The results can provide some basises for the simulation: the behaviors of concrete、steel and CFST are sensitive to the strain rate, the strength of them are improved with the increase of strain rate; HJC model is suitable for the simulation of the dynamic mechanical of concrete under different stress state and the numerical model can be corrected according to it; the bond-slip between steel and concrete has little influence on the dynamic behaviors of CFST.(3) The maximum dynamic displacements of the CFST columns subjected to blast loading were solved by using the method of equivalent single-degree-of-freedom system, it shows that the simplified theoretical method has a good agreement with the test results; the blast resistant performance of the circular cross section CFST column is better than rectangular cross section CFST column when the dosage of materials is the same.(4) The numerical models of CFST columns subjected to blast loading were established, and the models were corrected according to the experimental date. The dynamic response and the failure modes of them were analyzed, the influences factors to the blast resistant performance of CFST columns were studied, and the pressure-impulse diagram(P-I curve) was established based on the new damage criteria that defined based on the residual axial bearing capacity of CFST columns. The results show: the blast resistant performance of CFST columns is good, CFST columns tend to occur local damage when the explosive is near the columns, and it tend to occur overall damage when the explosive is far from the columns, the failure modes under overall damage condition are associated with the peak of the pressure and impulse. The strength grade level of the materials, the steel ratio and the cross section form have a certain influence on the blast resistant performance of CFST columns, and the axial compression ratio, the height of the column and the proportion distance have a great influence on it. The new damage criteria is independent to the failure modes of CFST columns, it can effectively reflect the damage extent of CFST columns.