Seismic performance of asymmetric isolated steel structures with different bracing systems

One of the effective methods to reduce the impact of earthquakes on structures and improve the seismic performance of structures is the use of seismic isolation system. In this paper, the seismic performance of asymmetric isolated structures with different bracing systems under near-fault strong ground motions is investigated. Nonlinear dynamic analysis are performed under the simultaneous application of horizontal and vertical components of seismic acceleration. For this purpose, three types of chevron, cross and zipper bracing systems in 5 and 10-story structures with 0%, 10% and 20% mass eccentricity have been studied. Nonlinear time history analysis is performed by seven selected accelerogram. First, the symmetrical structure was analyzed in fixed and isolated base states. Then, the asymmetric effect on two eccentricity cases 10% and 20% in the target structures was compared. The average of shear force, drift and rotation of floors and input energy to the structure are the parameters studied in this paper. With an increasing eccentricity of the structure, the energy absorption by the isolator is reduced and the base shear is increased. Among the different bracing systems, the energy absorbed by the isolation system in the structure with zipper bracing increased by 53% and the base shear rate decreased by 80%.Based on the analysis results, base-isolation in the structure with cross-bracing in symmetrical, and asymmetric has caused a reduction of more than 70% of the floor rotation compared to other bracing systems.