Axial compression behavior of double-skin FRP-concrete-steel tubular columns: Experimental and analytical investigations

Abstract

Double-skin tubular columns (DSTCs) with fiber-reinforced polymer (FRP) confined concrete have shown promising load-bearing capacity and ductile behavior under axial loading. A new variation of DSTC with concrete sandwiched between an outer FRP tube and a stiffened inner steel tube can provide additional benefits than the traditional unstiffened column form. The first objective of this study was to experimentally investigate the behavior of square-square (SS) shaped stiffened DSTCs with concrete sandwiched between outer FRP-tube and an inner steel tube. Experimental results of 22-test specimens are discussed and then analysis-oriented stress-strain model is proposed for the FRP confined concrete, quantifying the influence of stiffened steel tubes, stiffener characteristics and unconfined concrete strength used in the tests. The proposed confined-concrete model was then used to perform the finite element (FE)-based calibration study against test results for stiffened DSTCs with square-square (SS) cross-sectional shape. The stiffener properties varied in both experimental and analytical studies include quantity, layout or configuration, and cross-sectional dimensions. Based on the proposed confined concrete model, the FE-based calibration demonstrated superior agreement with the experimental results (2 to 5% average difference at critical stages of loading, i.e. “elastic”, “peak” and “ultimate” axial loads). The experimental and numerical based results were finally used to propose a simple equation for accurately predicting the axial load capacity of stiffened SS-shaped DSTCs.