Study on the Effect of the Position of X-bracing Arrangement in the Steel Structures with a Triangular Plan

In buildings with triangular plan, the center of mass and rigidity cannot geometrically match all possible directions of the earthquake. This will result in torsional moments in the stories causing the building to rotate around the center of rigidity. In this paper, via response spectrum analysis (RSA) and nonlinear static analysis, the seismic behavior of 5-, 10- and 15-story steel structures with a triangular plan is investigated by proposing 7 types of bracing arrangements in the plan. According to the analysis results, the most appropriate bracing arrangements in these seven proposed models in the triangular planes is the arrangement of braces in the middle of the triangle sides and continuous. This causes the center of mass to get closer to the center of rigidity, as a result of which, torsional moments and additional rotational displacements at the stories are decreased. The continuous braces reduces the lateral displacement of the structure about 38% and increases the displacement ductility ratio about 12%. Also, in structures whose braces cross each other at one point, the torsional strength of the system has been zeroed and in accordance with the ASCE7-16, they are considered to possess extreme torsional irregularity and the structures are therefore unstable.