Experimental study on CFST members strengthened by CFRP composites under compression

The concrete filled steel tubular (CFST) members become very popular in the construction industry and, at the same time, aging of structures and member deterioration are often reported. The actions like implementation of new materials and strengthening techniques become essential to combat this problem. This research work aimed to investigate the structural improvements of CFST sections with normal strength concrete externally bonded with fibre reinforced polymer (FRP) composites. For this study, compact mild steel tubes were used with the main variable being FRP characteristics. Carbon fibre reinforced polymer (CFRP) fabrics were used as horizontal strips (lateral ties) with several other parameters such as the number of layers, width and spacing of strips. Among thirty specimens, twenty seven were externally bonded with 50 mm width of CFRP strips with a spacing of 20 mm, 30 mm and 40 mm and the remaining three specimens were unbonded. Experiments were undertaken until column failure to fully understand the influence of FRP characteristics on the compressive behaviour of square CFST sections including their failure modes, axial stress–strain behaviour, and load carrying capapcity. From the test results, it was found that the external bonding of CFRP strips provides external confinement pressure effectively and delays the local buckling of steel tube and also improves the load carrying capacity further. Finally, an analytical model was proposed herein for predicting the axial load carrying capacity of strengthened CFST sections under compression.

► This research work aimed to develop optimum wrapping schemes for CFST members.
► The CFRP strengthening significantly increases the load carrying capacity.
► Data are used to develop design guidelines for FRP strengthened CFST members.