Mechanics of damage in reinforced concrete member under post-blast fire scenario

Abstract

Recent terrorist activities in the form of blast and its cascading effects in the form of fire have had devastating impacts in structures, posing serious safety issues in structural members. In this context, a numerical study is conducted here to investigate the mechanics of damage in a reinforced concrete (RC) wall panel exposed to post-blast fire. The study involves developing a three-dimensional (3-D) nonlinear finite element (FE) model considering material nonlinearity as well as geometric nonlinearity. The developed FE model of the RC wall panel is first exposed to blast scenario, where the dynamic effect of blast loading is incorporated using strain-rate-dependent models of concrete and steel. The subsequent transient thermo-mechanical analysis, considering pre-damaging effects of the RC wall panel, is carried out by duly incorporating the temperature variation in thermal and mechanical properties of concrete and steel reinforcing bars. Responses are compared in terms of out-of-plane deflection, variation in stresses and strains at exposed and unexposed faces, damage pattern, and nodal temperatures of the wall panel. It is concluded that the responses obtained under the cascaded extreme loading scenario demonstrate significant damage caused to the RC wall panel as compared to the damage induced when it is exposed to either of the particular hazards. Moreover, fire resistance rating of the wall panel decreases considerably under the extreme cascading effects. Hence, current design standards may be required to incorporate the pre-damaging effects of cascading hazard to safeguard civil infrastructures from such extreme accidental/ manmade threats.