Nonlinear finite element analysis of circular stiffened FRP-concrete-steel double-skin tubular columns (DSTCs) and experimental compressive behavior of multiple DSTC shapes

Abstract

A new variation of hybrid double-skin tubular column (DSTC) consisting of concrete sandwiched between outer fibre-reinforced polymer (FRP) and inner stiffened-steel tube shows better structural performance than its unstiffened conventional form. Vertical steel stiffeners placed on the outer surface of the steel tube can potentially reduce inner tubes’ local buckling and enhance composite interactions between column components, thus resulting in improved confined concrete behavior. The present study proposes an analysis-oriented confined concrete stress–strain model for nonlinear finite element (FE) simulation of circular stiffened DSTCs. Detailed FE analyses were performed using the proposed confined concrete model for validation against documented test results of circular DSTCs with parametric stiffener geometry variations. An excellent agreement was shown between numerical and test results (at most 5% errors at critical elastic, peak and ultimate axial loads). The numerical models captured well both the elastic and post-elastic behavior of stiffened DSTCs. Finally, 14-stiffened DSTC specimens of different cross-sectional shapes, i.e., circle-circle (CC), square-circle (SC) and square-square (SS) cross-sections were tested for investigating their behavior under axial compression. Stiffened DSTCs showed significantly increased axial load capacity (up to about 32% in this study) with enhanced ductility than unstiffened specimens. The SS-shape DSTCs provided with steel stiffeners at mid-flat sides of the inner steel tube manifested relatively better performance benefits than CC and SC shapes.