An improved 2DOF model for dynamic behaviors of RC members under lateral low-velocity impact

Abstract

Under lateral low-velocity impact, the RC slender members, i.e., beams and columns, commonly exhibit the local punching-shear as well as the global shear, flexural, flexure-shear and instability failure modes. However, the existing theoretical models are incapable of simultaneously predicting the above failure modes and the corresponding dynamic responses of RC members. This study aims to develop a two-degree-of freedom model (2DOF) model to predict the dynamic behaviors of RC members exhibiting the above-mentioned failure modes under the lateral low-velocity impact. Firstly, the combined dynamic flexural and shear resistance function of RC members is established and verified by rapidly concentrated loading tests on RC beams. Secondly, an improved 2DOF model is proposed by incorporating the combined dynamic resistance function, P-δ effect and the shear wave propagation effect for the local and global response stages of members. Then, the improved 2DOF model is comprehensively validated by eight series of existing drop hammer tests (165 scenarios), in terms of the failure modes, impact forces and mid-span deflections of RC members. It is further found that, under impact loadings, the failure mode of the static flexure-critical RC beams would transit to the punching-/flexure-shear failure, which is more sensitive to the impact velocity than the impactor mass, and can be effectively inhibited by increasing sectional shear capacity. Finally, aiming to assist the impact-resistant design and evaluation of RC members, the corresponding flowchart is given.