172 / 2022-04-30 13:57:30

Experimental study on seismic performance of elliptical concrete-filled FRP tubes with longitudinal steel rebars

FRP,Concrete-filled FRP tube,Elliptical column,Seismic behavior,Hysteretic curve,Numerical simulation

Fiber-Reinforced Polymer (FRP) composites possess many advantages, such as light weight, high strength, good corrosion resistance, easy fabrication and good insulation performance. The rational applications of FRP composites in civil engineering structures help to improve the corrosion resistance and to reduce the life-cycle resource consumption of the whole structure. Concrete-Filled FRP Tubes (CFFTs), which consist of a FRP tube filled with plain concrete and optional longitudinal steel rebars, are a novel type of structural member particularly attractive for new structures. When CFFTs are used as columns, the infill concrete is under axial compression and also subjected to lateral confinement from the FRP tube. This lateral confinement from the FRP tube can significantly increase both the strength and the ductility of the infill concrete. Existing studies on CFFTs are mainly focused on specimens with a circular cross-section, or a square cross-section, while studies on CFFTs with an elliptical cross-section are rather limited. Similar to circular CFFTs, elliptical CFFTs have a cross-section with a continuous curved circumference, leading to effective confinement to the internal concrete. Elliptical columns are attractive for engineering applications due to their excellent aesthetic appearance. Elliptical columns have different bending stiffness around the two axes of symmetry, which could be designed optimally according to engineering needs.



This paper conducted an experimental study on Elliptical CFFTs reinforced with longitudinal steel rebars (ER-CFFTs) under combined cyclic lateral loading and constant axial compression. The effects of elliptical aspect ratio and FRP tube thickness were investigated experimentally. For the elliptical cross-section, all specimens had the same major axis 2a (i.e., 300 mm), but with different minor axes 2b (i.e., 300 mm, 200 mm, 150 mm and 120 mm, respectively), leading to four different elliptical aspect ratios ρA=2a/2b (i.e., 1.0, 1.5, 2.0 and 2.5). For each specimen, a filament-wound glass FRP tube (GFRP) was adopted, which was fabricated in a professional factory using the filament-wound process with the fibers oriented ±80° with respect to the longitudinal direction of the FRP tube. Each ER-CFFT, which had a total height of 2150 mm, consisted of an elliptical column portion with a height of 1200 mm, a column footing with sufficient steel reinforcement (470 mm in height, 800 mm in width and 800 mm in length) and a column head with sufficient steel reinforcement (480 mm in height, 2a in length and 2b in width). The height from the lateral loading point to the top surface of the column footing was 1430 mm. Test results indicated that, ER-CFFTs had excellent seismic behavior even for the specimen with a large elliptical aspect ratio, and a thicker FRP tube could lead to better ductility. A numerical column model was established and implemented into OpenSees (Open System for Earthquake Engineering Simulation) to simulate the hysteretic behavior of ER-CFFTs, which was capable of providing reasonably accurate predictions.