Load bearing capacity of GFRP-strengthened tubular T-joints: Experimental and numerical study

Tubular joints are one of the most common connections in steel structures. Strengthening joints with Fiber Reinforced Polymer (FRP) material is rapidly gaining interest and has been the subject of extensive research due to its supreme characteristics as a reinforcing methodology. In order to investigate the behavior of such strengthened joints and the effects of joint geometry, a comparative experimental program together with relative parametric numerical analyses were carried out and the results were interpreted. The experimental program consisted of two full-scale tubular joints of different geometries (T1 and T2) which were reinforced by Glass/ Vinyl ester material (T1R and T2R). The specimens were subjected to a displacement control axial compression exerted by a 500 kN actuator. Based on the findings, as a result of GFRP application, a minimum increase of 42% in the ultimate static load-bearing capacity of the joints, and nearly 11% in the joint's initial stiffness was observed. Moreover, the potential debonding areas of the joints were found to be the intersection zone for both the saddle and crown lines. However, for the crown line, this area stretched up to the edge of GFRP strengthening on the steel substrate as well. Additionally, it was found that higher joint diameter ratios (beta) and chord thinness ratios (gamma) reduced the effectiveness of the GFRP reinforcement. Meanwhile, Joint thickness ratios (tau) had almost no effect on the reinforcement.

Automated summary

Strengthening tubular joints with GFRP can significantly increase their load-bearing capacity and stiffness. The potential debonding areas are at the intersection of the saddle and crown lines. The effectiveness of GFRP reinforcement is reduced by higher joint diameter ratios and chord thinness ratios, but the joint thickness ratio has little effect on the reinforcement.