Shear Mechanisms in Reinforced Concrete Beams under Impact Loading

Abstract

A well-instrumented drop-weight test program was developed to investigate shear failure modes of large-scale RC beams under impact loading. Test variables included beam span, transverse reinforcement ratio, impact mass, and impact velocity. The impact and reaction forces, and midspan deflection and accelerations at discrete locations along the beam were measured, and crack propagation was recorded using a high-speed video camera. Nonlinear finite element simulations also were carried out to study the feasibility of modern commercial software to reproduce observed behavior. Findings from the study indicate that as the impact velocity increases, specimens tend to fail in shear with diagonal cracks forming a shear plug near the loading point. These major diagonal cracks develop within a very short duration after impact when stress wave propagation has a significant influence on the impact responses, causing them to deviate from well-known behavior under static loading conditions. Providing additional transverse reinforcement was found to inhibit the development of shear cracks and the effect of stress wave propagation on impact response was more pronounced with increasing beam span.