Numerical analysis of axially loaded RC columns subjected to the combination of impact and blast loads

Abstract

This paper presents a theoretical study on effects of combined impact and blast loadings on the failure behaviors and dynamic responses of a typical reinforced concrete (RC) column commonly used in medium-rise buildings. In the view of absence in current testing facility for simulating the combined loading, this investigation is carried out using numerical simulations in LS-DYNA. The vulnerability of the RC column to several loading-related parameters including the loading sequence, the time lag (tL) between the onsets of the applied loads, the axial load ratio (ALR), the loading location, and the impact velocity (Vimpact) is ideally assessed using a damage index (DI) on the basis of the column residual axial load carrying capacity. In order to calculate the DI, a multi-step loading methodology is proposed based on the combinations of static axial, and transient dynamic loadings. This paper is an ideally numerical exercise to evaluate different loading scenarios on RC columns varying in terms of some new parameters including ALR and the loading location compared to those studied for beams in the previous studies. From the FE simulations, it is obtained that the combination of a middle-rate impact loading and a close-in explosion provides more intensive loading conditions when they apply at the same elevation on the column. However, the combination of an identical impact loading with a far-field detonation leads to more severe failures when they are applied at different elevations. In addition, the priority of impact loading rather than explosion provides more intensive combined loading scenarios and causes more severe spallation and global failures in the column. By evaluating the effects of the time lag parameter, it is found that the column experiences greater shear forces and more severe global damages when the sequent detonation is applied at the time of the initial peak impact force. Furthermore, for the combined loading scenarios in which the loads applied to the column mid-height, the sensitivity thresholds of the damage index to ALR and Vimpact parameters are different from those calculated under sole impact and explosion loadings.