Behaviour of GFRP-reinforced concrete circular columns under simulated seismic loading

Abstract

Columns in earthquake-resistant reinforced concrete (RC) structures need adequate confinement to exhibit stable seismic response with satisfactory level of deformability. Circular RC columns can be confined using spirals or discrete hoops. While the use of non-corroding fibre-reinforced polymer (FRP) reinforcement has been established as a viable substitute for conventional steel, the available code provisions for seismic design of FRP confinement reinforcement are overly conservative. This is due to the scarcity of the available research data, particularly those related to high-strength concrete (HSC) columns and those with different aspect ratios. That is, the linear-elastic behavior of FRP material could be of concern when combined with the brittle nature of HSC or implemented in short columns, which could be significantly influenced by shear stresses. A trailblazer research program was conducted to explore the seismic behaviour of glass FRP (GFRP)-RC circular columns, including experimental and numerical phases. The experimental work incorporated the construction and testing of fifteen full-scale GFRP-RC column-footing connections under concurrent axial loading and cyclic lateral drift reversals. The investigated parameters were the longitudinal reinforcement type, transverse reinforcement configuration, concrete compressive strength, axial load level and column aspect ratio. The numerical phase included the construction and validation of a three-dimensional nonlinear finite-element model (FEM) against results from the experimental phase. The validated FEM was, then, used to conduct a comprehensive parametric study investigating the effect of the practical range of concrete compressive strength, spiral pitch, axial load level and column aspect ratio on the behaviour of such columns. The results indicated the conservativeness of design provisions related to spiral pitch whereas the provisions of the Canadian Highway Bridge Design Code for lap splice length of discrete FRP hoops were found to be unsafe. Additionally, GFRP-reinforced HSC circular columns can exhibit stable seismic response with sufficient deformability when properly-confined. Unlike steel-RC columns, changing the aspect ratio insignificantly influenced the hysteretic response of GFRP-RC columns. Based on the results of this study, two new design models to predict the amount of FRP confinement reinforcement with remarkable accuracy were proposed.