Circular steel tubes filled with rubberised concrete under combined loading

The research on rubberised concrete (RuC) could promote the recycling of end-of-life tyres and reduce natural resource extraction. To mitigate the greatly reduced compressive strength and fully utilise the desirable characteristics such as improved ductility and energy absorption of RuC, confinement through a steel outer tube could be adopted. This paper investigated the effect of using circular steel tube as confinement of the RuC under axial, flexural and combined loading conditions. A total of 4 circular hollow tube sections with d/t (depth/thickness) ranging from 18 to 36 was used in this study. Three rubber replacement ratios (0%, 15%, 30%) by mass of the total aggregates were examined, along with 4 load eccentricities (0, 0.25d, 0.5d and bending) used to construct the interaction diagrams. As a result of the steel confinement, the difference in load capacity between RuC and normal concrete significantly reduced compared to the plain concretes. Additionally, RuC filled steel tube (RuCFST) members were more ductile than their normal concrete counterparts. The circular cross-section showed superior load carrying capacities compared to the square sections, due to a relatively uniform stress distribution in the cross-section. The interaction diagrams of RuCFST members could be reasonably predicted in terms of accuracy and safety of design. The tested moment capacity of RuCFST also greatly exceed the predicted values. This study has demonstrated the possibility of using RuCFST in applications where high energy absorption and ductility capacities were sought, for example, the structural members in seismic regions and flexible roadside barriers.