Elliptical FRP-Concrete-Steel Double-Skin Tubular Columns under Monotonic Axial Compression

Abstract

Hybrid FRP-concrete-steel double-skin tubular columns (hybrid DSTCs) are a novel form of hollow columns consisting of an outer FRP tube, an inner steel tube, and an annular layer of concrete between the two tubes. Due to the effective confinement of the two tubes, the concrete in hybrid DSTCs is well confined, leading to excellent ductility and strength enhancement. Hybrid DSTCs also have excellent corrosion resistence due to the effective protection of the outer FRP tube. However, existing studies mainly focused on hybrid DSTCs with a circular cross-section. When subjecting to different loads in the two horizontal directions, elliptical columns are preferred as they can provide different bending stiffness and moment capacity around two axes of symmetry without significantly reducing the confining effect of the FRP tube. This paper extends the existing work on circular DSTCs to elliptical DSTCs with a particular focus on four issues: the effect of elliptical aspect ratio (i.e., the ratio of the major axis to the minor axis of the outer elliptical cross-section), the effect of the FRP tube thickness, the effect of void area ratio (i.e., the ratio of the area of concrete void to the area of the outer elliptical section), and the effect of the cross-section of the inner steel tube (i.e., both rectangular and elliptical steel tubes were used). Experimental results show that, the averaged peak stress of the confined concrete in elliptical DSTCs increases with the increase in the elliptical aspect ratio, whereas the elliptical aspect ratio has no obvious effect on the ultimate axial strain; the cross-section shape of the inner steel tube has significant effect on the axial stress-strain behavior of the confined concrete in elliptical DSTCs; elliptical DSTCs with an elliptical steel tube exhibit much better ductility and strength enhancement than those specimens with a rectangular steel tube. A simple stress-strain model of confined concrete was proposed for elliptical DSTCs to account for the effects of the elliptical aspect ratio, the inner void, and the shape of the inner steel tube, which can provide reasonably accurate but conservative predictions.

A State-of-the-Art Review of FRP-Confined Steel-Reinforced Concrete (FCSRC) Structural Members

“…Therefore, it is generally not an economic option to construct pure FRP structures in practical applications. To this end, the combined usage of FRP composites and traditional construction materials (including steel and concrete) has attracted more and more attention in the research community [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31], with the aim to establish cost-effective and novel forms of structures with excellent structural performance.…”

“…Subsequently, capitalizing advantages of the FRP-confined concrete, steel reinforcement has been proposed to be used in FRP-confined concrete structural members to further enhance their deformation capacity and strength. Among these hybrid structural members, double-skin tubular members (DSTMs; see Figure 2a) [16][17][18][19][20] are popular. However, the DSTMs-which consist of an FRP tube as an external confining device and protective skin against environmental attacks, a steel tube as internal reinforcement, and concrete sandwiched between the two tubes-may experience the inward buckling of the steel tube under compression.…”

Compressive Behavior of Circular Sawdust-Reinforced Ice-Filled Flax FRP Tubular Short Columns

“…More recently, fiber-reinforced polymer (FRP) composites have been increasingly used in civil engineering because of their high strength-to-weight ratios, good design flexibility, and excellent corrosion resistance even under harsh environment [10][11][12][13][14][15][16][17][18][19][20][21][22]. In the 1990s, Mirmiran and Shahawy [23] proposed concrete-filled FRP tubular (CFFT) columns.…”

Effect of Cross-Sectional Aspect Ratio on Rectangular FRP-Concrete-Steel Double-Skin Tubular Columns under Axial Compression

“…Although circular columns and square columns are attractive as bridge piers, rectangular columns are preferred if such columns are subjected to different load levels in the two horizontal directions (Figure 1). Rectangular DSTCs could be designed to provide different bending stiffness and moment capacity around the two axes of symmetry according to the engineering requirements [23]. Rectangular FRP-confined concrete columns have received extensive research attention in the last decade [24][25][26][27][28][29][30], but experimental research on rectangular DSTCs is rather rare.…”