Experimental and numerical analyses of flexural behaviour of hybrid LRS FRP-concrete-steel double-skin tubular beams with eccentric encased steel tube

This study presents the results of the flexural behaviour of hybrid large-rupture-strain (LRS) FRP-concrete-steel double-skin tubular (DST) beams with eccentric encased steel tube. The unique design of these beams demonstrates excellent ductile potential, with a flexural ductility index greater than eight. The variation in eccentricity of the encased tube is found to be the key factor controlling the ductility index parameter. The hybrid beams were found to exhibit ductile flexural failures, with the fracture of the FRP laminate at the bottom being considered the precursor to ultimate failure. Non-linear finite element models and a simplified theoretical approach are developed, and good agreements are achieved when compared to the experimental data. The calibrated numerical model is used to perform parametric studies on the variation in the size of the inner tubes. The results revealed that the flexural resistance, in terms of load and moment, increases at a near-linear trend with the increase in tube diameters. However, an opposite trend was observed for the ductility of the beams.