Residual strength of reinforced concrete beams under sequential small impact loads

Abstract

Sequential small impact loads may not collapse structures directly but could weaken the strength of structures. This study aimed to investigate the impact of these sequential small impact loads on the strength of the reinforced concrete beams. First, six sequential impact loads were applied to the test specimens. Then, the residual static capacity of the impacted specimens was determined by the ultimate static load test, compared with those of undamaged specimens. The experiment was composed of 12 specimens having identical dimensions. The variable parameters were the magnitude of the axial load and shear reinforcement. Under the sequential small impacts, the axial load improves the impact performance. It reduces the tensile strain of the longitudinal reinforcement. Hence, the flexural tensile crack propagation is limited. In addition, the local damage at the impact location is minimized and the shear plug induced diagonal shear crack is prevented. The axial force is also able to diminish the adverse effect of the large spacing stirrups. Large impact load could alter the failure of a designed flexural critical reinforced concrete beam without axial load to the shear failure. Although the axial load improves the impact response, the Residual Resistance Index (RRI) decreases with axial load. For the damaged specimens with axial load, the ultimate static load is lower than the calculated concrete shear capacity and more severe diagonal shear cracks were found. It can be obviously said that the prior impact damage decreases the concrete shear capacity.