Evaluation of Seismic Damage to Non-structural Components in an Isolated Building During the 2022 Luding Earthquake

On September 5, 2022, a seismic event with a magnitude of 6.8 occurred in Luding, Sichuan, resulting in varying degrees of damage to non-structural components inside a seismic isolation-designed building located near the epicenter fault. Non-structural components constitute a substantial portion of the overall structural economic value, and their seismic damage is crucial for post-earthquake functional recovery. Consequently, this study presents the primary seismic damage to non-structural components within the building, employing a two-stage cascading analysis approach. In the first stage, nonlinear response history analyses of an 8-story frame-shear wall building's Etabs model were conducted, utilizing a set of ground motion records from nearby monitoring stations to simulate floor seismic response. In the second stage, employing common freestanding non-structural components, such as document cabinets inside the building as prototypes, nonlinear response history analyses of a zero-length rotation spring OpenSees model were performed. This analysis considered a suite of floor acceleration responses obtained from the previous stage to simulate rocking and overturning responses of non-structural components with varying sizes and slenderness throughout the building. Rocking and overturning responses of non-structural components subjected to both bidirectional and unidirectional inputs were examined, with a specific emphasis on the impact of the strong vertical component of the near-fault ground motion. The results indicate that the isolation system effectively reduces the horizontal floor acceleration response of the upper structure. However, the vertical peak floor acceleration is significantly amplified compared to the vertical peak ground acceleration. Furthermore, under bidirectional horizontal and vertical excitations, the rocking angles and the probability of overturning for freestanding non-structural components exceed those observed under horizontal unidirectional excitation. The influence of vertical excitation significantly increases the risk of damage to freestanding equipment. Therefore, in the seismic design of structures located near-fault sites, the substantial impact of intense vertical ground motion on internal non-structural components cannot be overlooked. © 2024 Sichuan University. All rights reserved.