Seismic performance of concentrically braced frame with hexagonal pattern of braces to mitigate soft story behavior

This paper aims to propose an innovative braced frame named hexa-braced frame for the improvement of the seismic response of conventional steel-braced frames. In the proposed system, vertical structural elements connect the V and inverted-V bracings over three stories to form the hexagonal bracing configuration, in which two stories are braced at the top and bottom. The objective is to distribute deformation demands along the height of the frame in order reduce the possibility of the soft-story mechanism, which is a concern in conventional steel-braced frames. To achieve this objective, the braced columns were designed to resist bending moments calculated by means of a simple analysis procedure. A set of 4-, 10-, and 20-story building models were used to evaluate the seismic response of the proposed bracing system through nonlinear static (monotonic and cyclic) and dynamic analyses. The results were compared with the responses of similar X-braced frame models as the benchmark. Analytical results reveal that the hexa-braced frame system has the desired structural behavior for the seismic resistant and can achieve the goal of uniform distribution of lateral deformation in order to reduce the soft-story failure.