Experimental and numerical investigation on behavior of CFRP-strengthened circular hollow section gap K-joints

• An efficient FRP installation technique was proposed to strengthen tubular K-joints.
• Experiments demonstrated the promotion of K-joint performance using the technique.
• Finite element models were developed and validated for K-joints with and without CFRP.
• Increasing layers of CFRP is efficient to promote ultimate loading capacity of K-joints.
• Formulas were proposed to calculate ultimate loading capacity of K-joints with CFRP.

An efficient technique of Carbon Fiber Reinforced Polymer (CFRP) application was proposed to promote joint capacity of general tubular K-joints fabricated from Circular Hollow Section (CHS) members. Using this technique, in order to understand the static performance of CFRP-strengthened CHS joints, a systematic investigation was carried out by means of both experiments and finite element method. Three CHS gap K-joints strengthened with CFRP sheets were tested under static axial force in braces, whilst one additional joint was served as reference joint without CFRP. The results of failure modes, deformation, Mises stress, strain intensity and load-bearing capacity of the joints were presented and compared. A series of finite element models were developed and validated for the joints with and without CFRP reinforcement. A parametric study was conducted to evaluate the effect of variables (length, layers and mechanical properties of CFRP) on load-bearing capacity. The research results revealed that the proposed technique of CFRP installation was efficient to promote performance of in-service CHS gap K-joints. Moreover, the layer of CFRP sheets has significant effect on load-bearing capacity, but the effect was negligible for either length or mechanical properties of CFRP sheets. Finally, formulas were proposed for calculating ultimate load-bearing capacity of CHS gap K-joints with CFRP composites, and their calculation results matched well with the experimental and numerical results respectively.