Transverse impact performance and design of rectangular reinforced concrete-filled steel tubular members

Impact is one of the accidental and potentially catastrophic actions that threaten structural safety, and therefore has gained increasing attention in recent decades. Investigations into the impact performance of concrete-filled steel tubular (CFST) members have been extensively reported. However, for their major derived structural members, reinforced-concrete filled steel tubular (RCFST) members with reinforcement required for fire safety concerns, limited studies have been conducted, especially with rectangular cross-sections. Thus, the dynamic performance and design of rectangular RCFSTs subjected to transverse impact loading were determined as the main focus of this work. Nine RCFST specimens were fabricated and then tested using a drop-weight testing system. The instantaneous force and deformation responses were recorded at high frequencies. A finite element model with the strain rate effect of materials well-considered was developed, and then used to identify the parameter sensitivities. A sequential equivalent transformation strategy, from rectangular RCFST to rectangular thick-wall CFST and then equivalent to square CFST stepwise, was employed to simplify and integrate the impact design of rectangular RCFSTs and CFSTs. Based on the results of a random database consisting of 200 groups of RCFST and CFST finite element models, design equations for predicting the maximum impact deformation of RCFSTs (and equivalent square CFSTs) were proposed, which are anticipated to facilitate relevant impact-resistant design of both rectangular RCFST and CFST members.