Design of CFRP-strengthened steel CHS tubular beams

External bonding of carbon fibre reinforced polymer (CFRP) sheets to the periphery of steel circular hollow sections (CHS) is a relatively new technique for structurally improving such sections. Design of CFRP sheets for strengthening tubular steel sections necessitates the prediction of the capacity of confined steel circular sections. This paper presents a design method for evaluating the capacity of CFRP-strengthened steel CHS subjected to bending. The hoop FRP reduces the effect of local buckling by restraining the tube wall. The influence of hoop CFRP is considered in the proposed method by taking its modulus of elasticity as a proportion of the elastic modulus of longitudinal CFRP. The excitation of the longitudinal CFRP minimises the effect of local buckling in the tube wall, which ultimately increases the local flexural stiffness and strength of the tube. The inclusion of the effects of strengthening parameters in current design rules, notably the Australian Standards AS/NZS 4600 (2005) and AS 4100 (1998) and the European Standard EC 3, is discussed. The strengthening effects considered here are those that arise from varying amount of CFRP, modulus of elasticity of the hoop fibre and steel yield strength. Strength curves for composite CFRP-steel CHS are provided to illustrate the extent of enhancement with the type of the parameter.

► We model the bending capacity of CFRP-strengthened steel CHS beams.
► We examine the effect of CFRP amount, CFRP modulus and steel yield stress.
► We simulate the design strength of CFRP-strengthened steel CHS beams.
► Increasing CFRP amount will increase design strength of strengthened CHS.