Influence of global stiffness and equivalent model on prediction of impact response of RC beams

Abstract

A spring-mass model is commonly used to predict the impact response of a beam. This type of models usually assumes the beam response is governed by flexural and/or shear response mode in deriving the equivalent structural parameters, i.e. equivalent stiffness and mass. However, it is also well-known that under high-speed impact the response during the impact could be limited to a localized area around the impact point. For such cases, the equivalent stiffness and mass estimated from the global response of the beam do not necessarily give good predictions of beam responses. This study numerically and analytically investigates the effect of the stiffness on the impact behavior of reinforced concrete (RC) beams. The numerical results have shown that the stiffness estimated from the global response does not reflect the true behavior of the beam during the first impact impulse. However, the stiffness governs the behavior of the beams at the final loading and free-vibration phase as the global mode dominates the response. Interestingly, a free beam, which has no boundary constraint, and the reference beam with boundary constraint show an identical behavior during the first impact impulse, demonstrating the impact response of the beam in the initial stage is independent of the beam global stiffness. In addition, an analytical model is proposed to predict the impact response of RC beams with reasonable agreement.