Time-Variation of Shear Forces Affecting the Impact Resistance of Reinforced Concrete Beams

One of the most hazardous scenarios for reinforced concrete (RC) members is due to the actuation of impact loads. Such impacts may be either accidental or induced events. Experimental research has demonstrated that the failure mode of RC beams is strongly governed by shear, due either to the formation of a shear plug close to the impact point or to the full development of inclined shear-bending cracks along the shear span. In order to analyze the shear strength under impact conditions, it is essential to understand how the development of inertia forces leads to a time-dependent distribution of shear forces and bending moments which differs significantly to those produced by quasi-static loads. In the paper, an experimentally-based determination of shear forces and follow-up of crack pattern is presented for RC beams tested under impact loads. Sectional forces' distributions are determined experimentally by measuring all the necessary terms involved in the dynamic equilibrium of forces: support reactions, impact force and inertia forces. While dynamic load cells have been employed to capture reactions and impact force, a Digital Image Correlation (DIC) technique supported by a high -speed camera has been used to obtain inertia forces from the accelerations derived from the displacement field in dynamic regime. Thereby, the evolution of shear forces at critical sections can be understood and the ultimate shear strength can be discussed with the help of M -V interaction diagrams..