FRP-concrete-steel tubular columns with a large inner void under lateral impact loading: Experimental study and finite-element modelling

By combining two concentrically placed tubes (i.e., an FRP tube as the external sheath and a steel tube as the inner reinforcement) and a sandwiched concrete layer, FRP-concrete-steel double-skin tubular columns (DSTCs for short) are an attractive type of hollow-core columns suitable for bridge piers working in humid and corrosive environments. The very limited experimental studies on DSTCs under impact loading had one or two of the following limitations: (1) the void ratio phi was far smaller than the size with practical engineering value; (2) the column diameter Dc was too small compared with the section size used in real engineering. To supplement the existing research, DSTCs with a large inner void and a practical large column diameter (i.e., phi = 0.73 and 0.82; Dc = 300 mm) were experimentally investigated subjected to lateral impact loading, with particular research attentions on parameters including the impact velocity, the boundary conditions, as well as the void ratio of the DSTC specimen. Test results indicated that: (1) the failure mechanism was primarily controlled by the boundary condition; a bending-dominant failure mode was observed for the DSTC specimen with the top end free and the bottom end fixed; in contrast, a small global lateral displacement and severe localized dent deformation was observed for the DSTC specimen with the top end simply-supported and the bottom end fixed; (2) the peak impact force, the impact duration as well as the residual lateral displacement had a positive correlation trend with the impact velocity; (3) a DSTC specimen with a larger void ratio had a lower peak impact force and a smaller global lateral displacement. Finite element model based on ANSYS/LS-DYNA was employed to simulate DSTCs subjected to lateral impact loading, which could yield results with reasonable accuracy.