Probabilistic Seismic Assessment of Floor Acceleration Demands in Multi-Story Buildings

The primary goal of seismic provisions in current buildings codes is to preserve life safety. Therefore, little attention has been devoted to the protection of building nonstructural components. However, they often represent a major portion of the total investment in building. In recent years the importance of nonstructural components has been recognized, especially in light of the observed performance of nonstructural components in recent earthquakes. The overall objective of this study is the improvement of our understanding the seismic demand of acceleration sensitive nonstructural components installed in the building structures.

In the first part of the study, acceleration demands in structures responding linearly to ground motions are investigated. A simplified method for quick estimation of floor acceleration demands is introduced. The method is based on rigorous structural dynamics but not using exact mode shapes but approximate mode shapes computed from a simplified continuous model consisting of a cantilever shear beam whose lateral deformations are coupled to a flexural beam. The effect of various structural parameters such as period of vibration, lateral stiffness ration on peak floor acceleration and floor response spectrum ordinates are studied by conduction response history analyses using a suit of ground motions recorded on firm soils are discussed. The study is extended to evaluate the effect of interaction between the primary structure and secondary system. A new response spectrum method is also presented for estimation of peak floor acceleration.

In the second part of the study, acceleration demands in structures responding nonlinearly to ground motions are investigated. Incremental dynamic analyses method are performed on generic nonlinear models by subjecting the models to ground motions scaled at increasing levels of intensities. The peak floor acceleration and floor response spectrum ordinates of structures with different number of stories and lateral resisting systems as the ground motion intensity increase are evaluated and discussed. Also the efficiency of different ground motion intensities for estimation of floor acceleration demands is investigated.