Hybrid double skin FRP – Steel column with rubberised concrete infill under axial loading

The use of scrap tyre rubber in concrete is an effective sustainable solution that lessens the accumulation of tyres in the landfill and related environmental hazards. Extensive research on the behaviour of rubberised concrete over the past few years has outlined some excellent mechanical properties of this material such as enhanced ductility, energy dissipation, and impact resistance but also an associated weakness of having reduced strength. In this paper, a hybrid double-skin tubular column with rubberised concrete infill is proposed to provide effective lateral confinement and longitudinal reinforcement to minimize the reduced strength of rubberised concrete. This double-skin tubular column called “hybrid RuDSTC” comprises an outer filament wound CFRP or GFRP tube, inner steel tube with rubberised concrete infill. An experimental investigation on the behaviour of the proposed column under axial compressive loading is carried out. The parameters of the investigation are the type and thickness of the FRP tube and the percentage of rubber aggregates such as 0%, 15%, and 30% by weight. Axial stress, axial strain, lateral strain, and failure shapes of the columns are determined and discussed. Results show that both the filament wound CFRP or GFRP tube and steel provide effective confinement to increase the compressive strength and the peak and ultimate strain capacities of the hybrid RuDSTC columns. An increase in the amount of rubber aggregates results in lower values of brittleness index which indicates better ductility of the columns. Performance of CFRP and GFRP enclosed columns based on their diameter to thickness ratio and the steel confined double-skin tubular columns are compared. The proposed novel hybrid column provides a sustainable solution with applications in seismic-prone regions and mining infrastructure.