Experimental study on the residual shear capacity of fire-damaged reinforced concrete frame beams and cantilevers

The mechanical properties of concrete and steel degrade after exposure to fire, thus the fire-damaged reinforced concrete (RC) members may not be able to satisfy the prescribed performance. Therefore, it is of great significance to identify the degree of fire damage for RC members or even the entire RC structure. For RC beams, comprehensive studies have been conducted on the residual flexural capacity after fire, but those related to the post-fire shear properties are barely found in the literature. In this paper, the shear tests of twenty-five beams--including frame beams and cantilevers--were carried out to investigate the difference in their shear behaviors before and after fire exposure. The parameters controlling shear capacity, such as shear span ratio, the concrete slab (i.e. the flange of the beam), and the stirrup spacing, were investigated. The experimental results indicated that both the shear capacity and the stiffness of the RC beams degraded after fire. The diagonal cracks of frame beams with fewer stirrups concentrated seriously, and their crack width increased considerably. Based on the test results, a simplified evaluation process was developed to evaluate the shear capacity of RC beams after fire, and the proposed formula was proven to be able to predict the residual shear capacity of fire-damaged RC beams with sufficient accuracy.