Experimental investigation on the seismic performance of GFRP-wrapped thin-walled steel tube confined RC columns

In order to eliminate buckling in thin-walled steel tube confined reinforced concrete (RC) columns, the external fiber-reinforced polymer (FRP) composite wraps may be applied. This paper reports the details and results of a series of seismic tests on FRP-wrapped thin-walled steel tube confined RC columns. A total of six full-scale circular cantilever columns were tested under combined constant axial load and lateral cyclic displacement excursions. The test specimens consisted of a control RC column, a carbon FRP (CFRP) confined RC column, a glass FRP (GFRP) confined RC column, a thin-walled steel tube confined RC column, and two GFRP-wrapped thin-walled steel tube (GST) confined RC columns of varying axial load levels. The diameter and height of the RC columns were 400 mm and 1600 mm, respectively, and the outer diameter to thickness ratio of the steel tubes was 135. The seismic responses of the test specimens were compared in terms of failure mode, hysteric behavior, ductility, stiffness degradation, energy dissipation capacity and equivalent viscous damping ratio. The effects of the GFRP wraps and the steel tube on the behavior of the GST confined column were revealed respectively. Test results showed that the steel tube confined column experienced local buckling and abrupt welding seam splitting resulting from high biaxial stresses, whereas such premature failure was prevented in the GST confined RC columns. For the specimens designed and tested in this study, both components in the GST contributed much to the seismic performance of the GST confined column, while the thin-walled steel tube was more effective than the GFRP wraps in improving the ultimate drift ratio. In addition, as the axial compression ratio was increased from 0.2 to 0.45, there was almost no decrease in displacement ductility for the GST confined columns.