Doctor of Philosophy
School of Civil, Mining and Environmental Engineering
Khan, Qasim Shaukat, Axial and flexural behaviour of circular concrete filled FRP tube (CFFT) columns with and without FRP reinforcing bars, Doctor of Philosophy thesis, School of Civil, Mining and Environmental Engineering, University of Wollongong, 2016. https://ro.uow.edu.au/theses/4775
Fibre Reinforced Polymer (FRP) reinforcement (tube and bar) has emerged as a viable alternative of steel reinforcement due to the deterioration of steel reinforced concrete members under harsh and corrosive environments. The FRP reinforcement exhibits higher ultimate tensile strength to weight ratio and corrosion resistance than steel reinforcement. In the last two decades, applications of FRP reinforcement for new structures were investigated. Concrete Filled FRP Tube (CFFT) for new column construction is one such application. A number of studies investigated the axial and flexural behaviour of CFFT columns. However, a limited number of studies proposed unified stress-strain models of circular CFFT columns under concentric axial load. In this study unified stress-strain models using compiled large databases of circular CFFT columns under concentric axial load were developed. The predictions of the developed unified stress-strain models matched well with the experimental strength and strain enhancement ratios of circular CFFT columns.
In recent years, FRP bar was investigated as a practicable alternative of steel bar in reinforced concrete members. A number of studies investigated the axial and flexural behaviour of FRP bar reinforced concrete members. However, a limited number of studies investigated the behaviour of FRP bar reinforced CFFT columns under concentric axial load, although most of the columns are subjected to eccentric axial loads. This study investigates the experimental and analytical behaviour of circular CFFT columns with and without FRP reinforcing bars under eccentric axial loads and four point-loads.
In this research study, the experimental program was designed to investigate the influence of FRP reinforcement and different axial load eccentricities on the load and ductility of circular CFFT specimens. The main experimental program comprised four steel Reinforced Concrete (RC) specimens and 16 circular CFFT specimens of 203 - 205 mm diameter and 800 - 812 mm height. The specimens in the main experimental program were divided into five groups: steel RC, Concrete Filled Carbon FRP Tube (CFRP-CFFT), Concrete Filled Glass FRP Tube (GFRP-CFFT), Carbon FRP (CFRP) bar reinforced CFRP-CFFT and Glass FRP (GFRP) bar reinforced GFRP-CFFT specimens. From each group, one specimen was tested under concentric axial load, one specimen was tested under 25 mm eccentric axial load, one specimen was tested under 50 mm eccentric axial load and one specimen was tested under four-point loads. Also, analytical axial-flexural interactions of the tested specimens using the equivalent rectangular stress block and layer-by-layer numerical integration methods were developed.
The experimental results showed that FRP bar reinforced CFFT specimens exhibited higher axial loads, flexural loads and deformations at peak loads than unreinforced CFFT and steel RC specimens. The analytical axial load-deformation curves of CFFT specimens tested under concentric axial load matched well with the experimental results. The analytical axial-flexural interactions of CFFT specimens and steel RC specimens were in good agreement with the experimental results.