SEISMIC FRAGILITY STUDY OF THREE-DIMENSIONAL ISOLATED STEEL FRAME STRUCTURE AND NON-STRUCTURAL COMPONENTS

Quantitative indices to evaluate the seismic performances of the superstructure, isolator and three types of non-structural components, i.e., sliding and overturning type equipment and suspended ceilings, are proposed for a three-dimensional (3D) isolated steel frame structure. Based on incremental dynamic analysis (IDA), the seismic fragility of the 3D isolated structure is studied by considering the structural and nonstructural behaviors. Based on a case study, the results show that the fragility of the 3D isolated structure is similar to that of the horizontally isolated structure. Their fragility is lower than that of fixed-base structure under far-fault ground motions but may become higher under high-strength near-fault ground motions due to excessive isolator displacement. For example, when a 9-degree rare earthquake occurs, the exceedance probability of immediate service state of the three-dimensional isolated structure and the fixed-base structure is 90% and 80%, respectively. The fragility of the sliding type equipment in the 3D isolated structure is lower than that in the fixed-base structure, and slightly higher than that in the horizontally isolated structure. The 3D isolated structure and horizontally isolated structure can effectively reduce the overturning probability of the overturning type equipment; when the PGA is 0.8 g, the overturning probability is only 7%, and the 3D isolated structure can significantly reduce the rocking angle of overturning equipment compared with the horizontally isolated structure. The fragility of ceiling is high for the fixed-base and the horizontally isolated structures, while it is effectively mitigated in the 3D isolated structure. The exceeding probability of ceiling corresponding to full operation under a near-fault 8-degree rare earthquake is only 1%.