Influence of loading-rate on the failure mode of reinforced concrete members

The lack of simplified methods for accurately predicting the response mode of reinforced concrete structural members (predominantly beams and columns) to impulsive loads indicates a lack of fundamental understanding of the complicated response of members in this situation. This often leads to engineers using over-simplified analytical methods or developing complex finite-element models, the reliability of which has been questioned. This paper presents the development of a theoretical model for predicting the initial demand on a reinforced concrete member subjected to impulsive loads, which can be used to show whether a brittle shear failure results. The model treats the response as being dominated by a wave phenomenon and employing a time increment approach to solve the equation of motion. Under impact loading, the model is able to demonstrate why higher velocity impacts are more likely to cause brittle shear failures in reinforced concrete beams than slower ones for the same impact energy. The paper concludes by extending the proposed method to predict the shear and bending demands on a blast-loaded member. It is hoped that through this new analytical model, design guidelines for new structures can be improved and better assessments of the vulnerability of existing structures can be carried out.