Experimental Study to Validate an Improved Approach to Design Acceleration-Sensitive Nonstructural Components

Nonstructural components in buildings can be subjected to very large acceleration and deformation demands during earthquakes. This is particularly true for flexible components that are tuned or nearly tuned to one of the modal frequencies of the supporting structure. To control the seismic demands in these situations, the authors have proposed a new design approach in which the connections between the structure and the nonstructural element are designed and detailed to experience nonlinearities to limit force and deformation demands. This paper summarizes an experimental campaign sponsored by the Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe (SERA) aimed at validating the proposed design approach. The research project involved subjecting 14 different specimens representing nonstructural elements, with masses ranging from approximately 200 kg to 800 kg, to severe floor motions recorded during the 1989 Loma Prieta and the 1994 Northridge earthquakes in three instrumented buildings in California. A total of 45 individual tests were carried out. The tests were conducted at the EQUALS laboratory shake table at the University of Bristol. Mass and stiffness were carefully selected in each specimen to have vibration periods that resulted in both non-tuned and tuned components to modal frequencies of the supporting structure. Furthermore, some of the tuned tests involved components tuned to the fundamental mode while others were tuned to the second mode of vibration of the supporting structure to examine possible differences. Lateral strength and primary energy dissipation were provided by two steel plates with rotations restrained at both ends and loaded out-of-plane. The tests demonstrated how the proposed approach greatly reduces force and acceleration demands while also reducing lateral displacement demands. Furthermore, tests also demonstrated that the proposed approach reduces the response sensitivity to the period ratio of the nonstructural element to that of the supporting structure leading to a reduction in seismic demands uncertainty.