Experimental behaviour of hybrid FRP-concrete-steel double-skin tubular arches

Hybrid FRP-concrete-steel double-skin tubular members (DSTMs) are a recent development that exploits the advantages of FRP composites (e.g., corrosion resistance, high strength-to-weight ratios and tailorability of material properties) to achieve high-performance and durable structures. Hybrid DSTMs consist of an annular layer of concrete sandwiched between an outer FRP tube and an inner steel tube. This paper presents a preliminary experimental study designed to investigate the feasibility of using the DSTM cross-section in arches for use in bridge construction (i.e. double-skin tubular arches or DSTAs). The fibres of the outer FRP tube are oriented close to the hoop direction to provide confinement to the concrete annulus. The inner steel tube, while also providing confinement to the concrete annulus, is mainly used to provide the steel tensile reinforcement for the section to resist bending. The inner steel tube also acts as propping during the construction process while the outer FRP tube serves as the formwork during concrete casting, thus considerably simplifying the construction process and reducing the labour cost. The experimental programme presented in this paper consisted of three tests on hybrid DSTAs subjected to two closely-spaced point loads near the mid-span covering two different FRP tube thicknesses and two steel tube locations (i.e., concentric and eccentric steel tube positions). The experimental results are presented and interpreted to understand the behaviour of hybrid DSTAs, particularly how the FRP tube thickness and inner steel tube eccentricity affect the behaviour of hybrid DSTAs.