Seismic response and sensitivity of primary-secondary systems

Seismic performance of light secondary systems anchored or attached to primary structures is crucial to their integrity and serviceability under severe earthquakes. Damage to secondary systems could be just as disastrous as damage to the primary structure itself. The goals of this study are to better understand the dynamic characteristics of secondary systems mounted on the elastic and inelastic primary structure in a seismic environment, and to provide practical considerations of secondary system seismic design based on the selection of optimum structural parameters.; Sensitivity analysis is one of the important tools which provides engineers with methods for investigating or minimizing the effects of parameter deviations. This investigation starts with introduction of a stochastic response sensitivity measure to primary-secondary systems in the time domain, and decoupling methods are proposed to deal with the high dimensionality associated with moment equations by partitioning them into several sub-equations. It is shown that this sensitivity measure can be used for a quantitative assessment of secondary system response in the elastic and inelastic primary structure.; Under severe earthquakes, most structures are designed to yield, while many secondary systems are designed to remain essentially linear to ensure functionality during earthquakes. Based on this consideration, the stochastic response and reliability of a single-degree-of-freedom secondary system attached to single- or multi-degree-of-freedom yielding primary structures are considered by using equivalent linearization and digital simulation. A detailed analysis which includes mean-square response, coefficient of excess, reliability, response probability density and nonlinear modes of the secondary system is carried out under white and filtered white noise excitations. Some useful results are presented, and application of these results to design is commented upon.