Experimental and nonlinear FE simulation-based compressive behavior of stiffened FRP-concrete-steel double-skin tubular columns with square outer and circular inner tubes

Abstract

Double-skin tubular columns (DSTCs) confined with outer fibre-reinforced polymer (FRP) and stiffened inner-steel tube shows more promising axial stress-strain behavior for sandwiched concrete than its traditional unstiffened form. This study experimentally investigated the compressive behavior of stub-type stiffened DSTCs consisting of square-shaped, filament-wound outer glass FRP and circular inner steel tubes. The first-ever finite element (FE) simulations were performed to validate the test results of 12 square-circle (SC) shaped DSTCs (about 2 to 6% average errors at critical elastic, peak and ultimate axial loads) for various parametric variations in stiffener properties on inner steel tube, such as quantity, configuration for the similar total stiffener area, effective placement, and stiffener cross-section dimensions and shape. An analysis-oriented axial stress-strain model is proposed for confined concrete in stiffened DSTCs of SC shape using the experimental and FE-based results. An enhancement of about 43% was observed in the axial load capacity of the stiffened DSTCs compared to the unstiffened counterparts. Finally, this study proposes a simplified axial load-bearing equation for estimating the peak axial load capacity of stiffened DSTCs. On comparing proposed model predictions and an existing formulation from the literature with actual axial load capacity values, the proposed axial load-bearing equation showed higher accuracy (about 8% maximum disparity) on an extended dataset of 49-stiffened DSTCs.