Comparative study of different strengthening methods for circular hollow section K-joints

Various factors, such as building function improvement and loading increases, may necessitate the reinforcement of circular hollow section (CHS) truss joints. This study proposed an innovative method for strengthening CHS joints by partially filling the chord with grout (PFG) and suggested three additional effective methods, namely welding tubes (W-T), welding stiffeners (W-S) and pasting Carbon Fiber Reinforced Polymer (CFRP) sheets. To comprehensively investigate these methods, three CHS K-joints were designed, each exhibiting different failure modes. Subsequently, a comparative analysis of the failure modes and structural performance for these joints was conducted though finite element analysis, considering a shear modified GTN model. Finally, an evaluation of various strengthening methods was performed using a multi-criteria decision-making (MCDM) method, based on the Analytic Hierarchy Process (AHP) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method. The analysis results demonstrated that the W-T and W-S methods exhibited the significant improvement in the structural perfomrance in most cases. The former effectively migrated the buckling of compressive brace, while the latter prevented punching shear. The CFRP method had the advantage of simultaneously reducing the Mises stress on both the chord and brace. The PFG method proved effective in preventing plasticity deformation of the chord and increasing the structural performance of compressive brace. In the AHP-TOPSIS method, the W-T, W-S, and PFG methods were recommended for three designed CHS K-joints respectively. The analysis in this study can help engineers in making more informed decisions when designing reinforcement methods.