Design of short CFRP-reinforced steel tubular columns

This paper presents the design and experimental evaluation of externally bonded carbon fibre-reinforced polymer (CFRP) sheets for strengthening circular steel tubular short columns. In addition to its ease of handling due to its light weight, the high-strength CFRP sheet can provide a degree of restraint to delay buckling of the thin steel wall. Ten short cold-formed steel circular hollow section (CHS) columns, with externally bonded orthogonal (hoop and longitudinal) CFRP sheets, were tested under axial compression. The experimental results indicate that enhancement of the axial section capacity is possible by fibre-reinforcing the steel tube. The design variables investigated to evaluate the strengthening efficiency include the steel yield strength, the modulus of elasticity of the hoop fibre, and the amount and configuration of the fibre reinforcement. Design curves predicting the section capacity of composite steel–CFRP tubular short columns are calculated based on current design guidelines for steel columns. The results highlight the ease of the use of such curves in the FRP strengthening or retrofitting design of tubular columns for section capacity enhancement.

Research highlights
► Combined hoop and longitudinal CFRP reaches the yield capacity of CHS tubes.
► Strengths are increased for tubes strengthened with higher amount of CFRP.
► Design strength curves for CFRP-reinforced steel columns have been presented.