Analysis of internal explosion load characteristics and dynamic behavior in RC box structures

In a reinforced concrete (RC) box structure, the dissipation of blast waves is restricted, and damage to the structure can be intensified due to multiple reflections. To thoroughly investigate the load characteristics and dynamic behavior of internal explosions in an RC box structure, the applicability of the finite element method was verified by replicating internal explosion tests on fully enclosed and semi-enclosed (with venting openings) RC box structures. Based on this, numerical simulations of internal explosions were conducted for the prototypical RC box structure and the type of terrorist bombing attacks specified by the Federal Emergency Management Agency under three explosion scenarios and four venting areas. The influence of venting area on the load characteristics at the inner surfaces and corners, the load distribution on the inner surfaces, and the time histories of displacement and velocity at the centers of the inner surfaces under internal explosion loads were explored. Additionally, a formula for calculating the total impulse of the structure’s inner surface was proposed, considering both the venting area and the spatial distribution of the impulse. The results show that the venting area has a negligible effect on the overpressure, while the impulse decreases exponentially with increasing venting area. The load distribution characteristics on the structure’s inner surface are significantly influenced by the structural dimensions, exhibiting an indented or W pattern. The maximum displacement at the centers of walls and slabs is reduced by about 50% as the venting coefficient changes from 0.457 to 1.220. Finally, based on the total impulse and maximum displacement response of each component under free-field explosion loads, a calculation method for the impulse and damage enhancement coefficient was proposed based on the venting area, effectively predicting the internal explosion load and the structure’s dynamic behavior at various venting coefficients.