Quantification of the seismic performance factors of steel hexagrid structures

Abstract

In recent years, structural systems with innovative configuration have attracted the attention of engineering communities. This study aims to evaluate the response modification factor, R, of a hexagrid structural system under seismic loads. Hexagrid systems are composed of diagonal and vertical elements to form hexagonal grids constrained by mega columns. They behave like tube type structural systems. To evaluate the seismic performance factors of new lateral resisting systems, a standard methodology has been provided by FEMA P695. Regarding this methodology, a 3D group of 3-, 9- and 21-story archetypes with different diagonal angles of 33°, 45° and 53° were designed with an assumed R factor. The considered R factor was evaluated based on the acceptance criteria of FEMA P695 using nonlinear static (monotonic and cyclic) and incremental dynamic analyses. To this end, the collapse fragility curves were provided to investigate the safety margin of archetypes against collapse during the earthquakes. The results indicated that the R factor of 4 satisfied the acceptance criteria, so it is applicable for the design of hexagrid structural systems. Based on the analytical results, the hexagonal pattern with a diagonal angle between 30° and 40°provides a high structural efficiency for hexagrid systems.