Displacement-based seismic design of non-structural building elements

Damage observed during past earthquakes, as well as recent loss estimation studies, have demonstrated the importance of the seismic design of non-structural elements. In a performance-based seismic design framework, the achievement of adequate performance objectives is not only related to the performance of the structure but also to the response of nonstructural elements. Because of lack of information on the seismic performance of non-structural elements, current seismic design provisions are either empirical in nature or based on judgement and lack clear definitions of performance objectives under specific seismic hazard levels. Current seismic design provisions are generally based on an empirical force-based seismic design approach. To address these shortcomings, this paper proposes a direct displacement-based methodology for the seismic design of non-structural elements in buildings. The proposed displacement-based design procedure applies mainly to acceleration-sensitive non-structural elements suspended or anchored at a single location (floor) in the supporting structure and for which damage is the result of excessive relative displacements. Examples of such acceleration-sensitive non-structural elements are suspended building utility systems, such as piping systems and cable trays, and anchored, free standing and vibration isolated building utility systems or contents. The design of the seismic restraints for a horizontal mechanical piping system suspended from the top floor of a generic case-study six-story steel moment-resisting frame building assumed to be located in high seismic site in the Western United States (US) was performed both according to the proposed direct displacement-based procedure and to the force-based design procedure of the ASCE 7-16 Standard in the US. Both design alternatives were evaluated through nonlinear time-history dynamic analyses in order to evaluate the effectiveness of the direct displacement-based design methodology as well as the influence of the design assumptions needed to perform the force-based design procedure.