Impact performances of RC beams at/after elevated temperature: A meso-scale study

Abstract

Impact (or blast) and fire always take place concomitantly and threaten the service life of engineering structures. Combined effect of high temperature and strain rate on the mechanical behaviors of reinforced concrete (RC) structures has attracted much attention of researchers. In this work, a three-dimensional meso-scale simulation method was established to study the combined effects of high temperature and strain rate on the failures of RC beams. In the method, the nonlinear interaction between concrete and longitudinal rebar was taken into account by using a bond-slip relationship. A two-step analysis method (thermal transfer analysis followed by impact analysis) was adopted. Mechanical analysis was carried out to understand the failures of RC beams under impact loading after fire exposure. In addition, impact responses of RC beams under fire exposure and after cooling down were compared and analyzed under different fire durations. The effects of impact mass and velocity on the impact performances of RC beams after fire exposure were discussed. It is found that the proposed meso-scale numerical model can effectively simulate the failures of RC beams subjected to impact loadings. Under impact loadings, RC beams after fire exposure show more serious damage while have better deformation capacity compared to the RC beams at room temperature. Fire duration has a significant influence for the impact behaviors of RC beams no matter whether they are cooled down or not. Compared to RC beams which are under fire exposure for >60 min, specimens after cooling down are subjected to less damage at all the involved temperatures. The difference is widening along with the increase of fire duration. Besides, the response of the RC beam after fire exposure is affected remarkably by both impact mass and velocity.