Response of secondary systems to seismic excitation

In this dissertation the response of secondary systems to seismic excitation is investigated. A secondary system is a piece of equipment or a lighter appendage to a more massive primary structure which receives external excitations indirectly through its host structure. Assumption of linear behavior for both primary and secondary system is made in most parts in the analysis. Parametric excitations due to vertical ground motion and hysteretic behavior of the primary system under severe loading are treated in two separate chapters. A general procedure is first developed to formulate the system of equations for a combined primary-secondary linear system in which secondary systems are attached to a primary system at an arbitrary number of locations. Successive chapters are devoted to studying the effects of different factors on the behavior of a particular type of the combined system; namely, a multi-story primary structure supporting a secondary equipment, idealized as a single-degree-of-freedom linear oscillator. We list the following major findings of this study: (1) The two approximation procedures to calculate the response of a secondary system to seismic excitations developed in this dissertation are accurate and efficient, and can be applied to light or moderately heavy equipments. (2) Parametric studies suggest that greater amplification occurs as an equipment is tuned to lower building modes. (3) The equipment response is sensitive to the equipment mass, damping in the building, and the location of the equipment. (4) Soil compliancy can affect equipment response significantly. A greater number of modes should be employed when soil-structure interaction effects are important. (5) Protective devices between the equipment and the supporting floor of a building can reduce the equipment response by an order of magnitude. In this dissertation we consider cushioning devices constructed of linear, viscoelastic materials. (6) Vertical ground motion and gravity effect can both increase equipment response. (7) If a building is forced into the nonlinear regime due to intense seismic excitations, the equipment response can be quite sensitive to the parameters of the nonlinear model.