Method and experimental study of strengthening circular hollow section T-joints by partial filling with cementitious materials

Abstract

Circular hollow section truss joints may need to be strengthened for various reasons. This study evaluated a new method for strengthening such joints by partially filling the chords with cementitious materials, including grout and mortar. Taking T-joints as an example, the proposed strengthening process was described and experiments were conducted on six joints (four strengthened and two unstrengthened) under axial compression or tension applied to the braces. The failure modes and structural behaviors of the joints before and after strengthening were compared, and the effects of the strengthened length, filling material, direction of brace loading, and presence of temporary openings in the chord on the performance of the T-joints were investigated. The results demonstrated that: the strengthening method was viable and effective, the T-joint filled with 1d0 grout (mortar) exhibited a 70% (33%) improvement in initial stiffness and a 50% (36%) improvement in ultimate loading capacity; the use of grout was more efficient and convenient for construction than mortar; the initial stiffness and ultimate loading capacity of the strengthened T-joint was also improved when the brace were under tension; the temporary openings cut in the chord during the strengthening process had a little effect on the performance of the T-joint, with reductions of 11% and 9% in initial stiffness and ultimate loading capacity, respectively. Thus, the performance and safety of the joints can be ensured if reasonable design and protection measures are implemented.