Axial compressive behaviour of CFST column externally reinforced by CFRP strips – A design of experiments approach

The purpose of this research is to investigate the influence of CFRP strips wrapping scheme (partial wrapping) in strengthening of CFST column subjected to axial compression. To complete the experimental investigation in an economical way, the central composite design (CCD) of the response surface methodology (RSM) was used to design the experiments. Based on the CCD experimental model, 9 unique tests were performed and the failure mode of the specimens, load–deformation behaviour, ultimate strength and ductility behaviour were studied. The test results showed that externally bonding CFRP strips is an effective approach to restraining axial deformation and enhancing the ultimate capacity of the column under compression. By bonding three layers of CFRP strips, the deformation of the columns was restricted to a maximum of 55.78% and 50.27% compared to the column bonded with one layer, when set at spacings of 20 mm and 30 mm, respectively. The ANOVA, Pareto chart and contour plot of RSM revealed that the layers of the CFRP wrapping scheme was more significant than the strips spacing in increasing the strength capacity of the CFST column. The suitability of design models proposed in various literatures for predicting the strength capacities of CFST columns strengthened with CFRP wrapping scheme was also examined. A simple design model, derived considering the column geometry and material strength of column and CFRP composites, was proposed to predict the axial strength capacities of CFST short columns confined by CFRP strips by using regression analysis. The proposed design model provides a more accurate and reasonably stable prediction compared with other existing design models.