Performance and design of RAC-filled steel RHS beams

Abstract

Research on steel hollow sections filled with recycled aggregate concrete (RAC) has been recently gained attention across the world. This is because the RAC-filled steel hollow section reuse the waste concrete, while, still achieving good structural performance. This paper studies the static performance of RAC-filled steel rectangular hollow section (RHS) beams. Ten beams with various recycled coarse aggregate (RCA) replacement ratio (r), depth-to-width ratio (β) and width-to-thickness ratio (B/t) were tested. The results show that, after the mid-span deflection exceeds 6% of effective span, the top flange of the tube and part of the adjacent side walls of the tube buckled in the pure bending zone for all tests, whilst cracking was observed at the bottom flange of the tube within pure bending zone of some beams. Accordingly, for the concrete core, both crushing at the tube buckling position and cracks extended towards the compression zone are observed. The moment-deflection (strain) relationship of the specimens can be divided into three key stages, namely, elastic, elastic-plastic and hardening. In general, moment capacity and flexural stiffness of the specimens reduce with the augment of B/t and the decrease of β under the same width. A finite element (FE) model that can efficiently reproduce the failure process and moment-deformation curves of RAC-filled steel RHS beams is also developed, and the FE is further used to discover the influence of r and β on working mechanism of such composite beams. Finally, based on the parametric analysis, the design equations for moment capacity of RAC-filled steel RHS beams are developed, and the accuracy of the simplified equations is verified by the experimental results. Meanwhile, the test results also proved that the approach in ACI 318 code is the more suitable method for the flexural stiffness prediction of RAC-filled steel RHS beams.