Seismic Performance of Rectangular Hollow Section X-Joints Subjected to In-Plane Bending Moment

This paper presents a study on the seismic performance of rectangular hollow section (RHS) X-joints subjected to in-plane bending moment (IPBM). The study began by testing two RHS joint specimens with varying brace-to-chord width ratios (β) under quasi-static cyclic IPBM loading. The results showed that the final failure mode of the specimen with the large β value (β = 1.0) is the tearing of the weld near the brace root, while the specimen with the medium β value (β = 0.83) failed due to the tearing of both the weld and the adjacent chord face. The seismic performance of the X-joints depended considerably on the β value. The increase in β remarkably improved the strength of the X-joints but at the cost of energy dissipation capability, deformability and ductility. Our experimental results also demonstrated that the current code equations remarkably underestimate the flexural strength of RHS X-joints, while the modified equations that take the weld size into account can predict it well. In addition, the reason behind the experimental observation can be further explained by FE analysis and the proposed elastic-support plate analytical model.

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