Equivalent viscous damping for non-structural building elements

Earthquakes that have struck densely built regions during the last decades in highly populated regions have demonstrated the need for reliable methodologies to perform the seismic design of non-structural building elements that are damaged due to inertia forces arising from horizontal floor accelerations. Performance-based seismic design of nonstructural elements, through a direct displacement-based design procedure, has been recently proposed to this end. This procedure is based on the concept of equivalent linearization of the response of nonlinear non-structural systems. An essential aspect of this process involves quantifying the amount of energy dissipated by a nonlinear non-structural element at its maximum expected displacement response. Energy dissipation in direct displacement-based design is usually represented through an equivalent viscous damping ratio. The first step in quantifying this parameter for some of the multitude of non-structural element typologies consists in gathering and processing experimental data that can describe the variation of the global equivalent non-structural viscous damping ratio with non-structural displacement amplitude relative to the supporting structure through an equal area approach. This first step gives not only a good estimate of the effective energy dissipated by nonlinear non-structural elements when subjected to floor acceleration time histories, but also reveals important hysteretic and mechanical properties of the same systems. In this work, some examples of test results performed on acceleration-sensitive non-structural elements available in the literature are processed in order to develop relationships between non-structural displacement relative to the supporting structure and equivalent non-structural viscous damping.