Fiber reinforced polymer (FRP) has been increasingly used in combination with concrete, steel, and other materials to form novel composite structural members owing to its excellent durability and high strength-to-weight ratio. Recently, a novel type of FRP-steel-concrete composite member (FSCM) including a truncated elliptical FRP tube and a concrete-encased steel I-section, was developed at The Hong Kong Polytechnic University. FSCMs can serve as ductile coupling beams in coupled shear wall systems, or as columns when lateral loading in one principal direction is considerably larger than in the other. An experimental study on compressive behaviour of such FSCM based on tests of 18 specimens (including 13 FSCMs and five corresponding concrete-filled FRP tubes) are presented in this paper. The test parameters include the thickness of FRP tubes and the cross-sectional dimensions of the embedded steel I-sections. It is shown that FSCMs with properly designed FRP tubes and steel I-sections can provide effective lateral confinement to the concrete infill, enabling the specimens to achieve satisfactory load-carrying capacity and ductility. The additional confinement provided by the steel I-section can increase the axial strength of the confined concrete in the post-yielding stage. Within the range investigated, variations in the steel I-section dimensions have limited influence on the overall structural performance of the FSCMs, whereas the FRP tube thickness exerts a more significant effect.
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