Post fire blast-resistances of RPC-FST columns using improved Grigorian model

Grigorian model is a popular and robust elasto-plastic model in describing the behaviors of rock-like material under intensive loading, but it neglects the dilations of fractural medium after wave front and the relaxation characteristics of crushed medium. This paper is devoted to enrich the original Grigorian model, and the user specified subroutines of improved Grigorian model are implemented in LS-DYNA codes. In new model, the relaxation equations are introduced to characterize the current yield surface migrating between original and residual yield surface, and the equations of states are also proposed based on Mie-Grüneisen equations. The blast-resistances of Reactive Powder Concrete-Filled Steel Tubular (RPC-FST) columns after exposure to ISO-834 standard fire are predicted by using improved Grigorian model, in which the thermal effects are involved to consider the heat conduction. It is indicated that fire exposures cause significant degradations of material properties, and have remarkable effects on the blast-resistant capacities of RPC-FST columns. The dynamic behaviors of RPC-FST columns under blast loading can be well simulated, and the numerical results are in good agreement with the data in blast-resistant test. Results show that the deformations of RPC-FST column are transferred from bending types to bending-shear types as scale standoff distances decrease. Evident plastic deformations can be observed at mid-span section of RPC-FST column as fire durations increase and typical bending failures are induced. In addition, the blast-resistant capacities of RPC-FST columns are more sensitive to fire durations than to scale standoff distances. Numerical simulations illustrate that the improved Grigorian model is better than original Grigorian model, and well-suited for describing the behavior of confined concrete subjected to blast load.