Energy Dissipation Platforms Based on Wire Rope Isolators for the Seismic Protection of Equipment

Abstract eng:
This paper summarizes the developments of experimental studies to assess the seismic performance of energy dissipation platforms based on wire rope isolators for the mitigation of the seismic effects on equipment located in different floors of different buildings. Two types of platforms supporting simulated equipment were tested: (1) platforms consisted of steel plates sandwiched by wire rope isolators in different configurations, and (2) a platform consisted of two steel plates sandwiched by a set of wire rope isolators and a set of rolling balls. Simulated equipment comprised non-slender rigid blocks and slender frames. Platform-simulated equipment settings were subjected to earthquake shaking of different intensities from measured accelerations records on multistory instrumented buildings, from past experimental testing, and from numerical simulations. These studies are aimed: (1) to experimentally evaluate the three-dimensional seismic performance of several platforms based on different configurations of wire rope isolators; (2) to assess the seismic energy-absorbing capacity of the platforms and their effects on the seismic response of slender frames holding equipment; (3) to characterize the seismic performance of new configurations of wire rope isolators to reduce/eliminate rocking responses; and (4) to study the effectiveness of a hybrid frictional energy dissipation platform based on wire rope isolators and rolling balls. The experimental responses demonstrated that the energy absorbing capacity of platforms based on wire rope isolators can control deformations of slender rigid frames. This outcome suggests that to secure the effectiveness of the platforms controlling deformations on slender frames, the frames that the platforms support must be relatively rigid. As expected and because of the slenderness of the frames supported by platforms that provide three-directional coupled flexibility, seismic responses of slender frames were controlled by rocking on the platforms based on wire rope isolators configured in shear/roll, and in compression/shear/roll. Proof of concept studies demonstrated that rocking may be controlled when adjusting the distance between the equipment’s center of mass and the center of stiffness of the platform by rotating the isolators. Asymmetrical arrangements of isolators in shear and in roll lead to different effective fundamental periods in the horizontal directions of the platforms. The asymmetric lateral stiffness provided by the wire ropes configuration on the platforms may be favorable when defining the dynamic properties of the platforms to protect equipment at different floors and in buildings with asymmetric plan configurations. The rolling balls increased significantly the effective damping ratio of the hybrid frictional isolation platform. The first mode equivalent damping ratio was up to 29%, and the restoring stiffness of the system is controlled by the effective stiffness of the wire rope isolators on the arrangement.

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