Seismic Demands for Single- and Multi-Story Wood Buildings

This report provides quantitative data on the seismic demands imposed by ground motions on structural systems that are representative of woodframe structures. The emphasis in the presentation is on the use of story displacements and story strength as primary engineering demand parameters. The results of this study are based on extensive simulations, using a wide range of important structural system parameters and a set of forty ground motions to generate representative seismic demands through nonlinear time history analyses and statistical evaluation of response data. The demands assessment process consists of the following components:

· Development of representative sets of ground motions
· Consistent scaling of ground motions to specific hazard levels
· Evaluation of experimental results for the purpose of improving analytical models
· Development of analytical component models that closely simulate experimental results, including monotonic and cyclic strength deterioration
· Utilization of these models in incremental dynamic analyses (IDAs), and representation of the IDA results in a format useful for performance evaluation and for design.
· Utilization of these models to develop demand information in an alternative representation scheme, called the performance spectrum.
· Utilization of these models for assessing the collapse capacity of structural systems. Collapse capacity assessment implies (a) evaluation of the ground motion intensity that will cause collapse of a given system, (b) evaluation of the structure strength and deformation capacity needed to prevent collapse under a given set of ground motions, and (c) evaluation of the weight (mass) that will cause collapse of a structural system of given characteristics at a given hazard level.

Much of this study is concerned with single-story buildings that can be represented by SDOF systems. In the last chapter it is demonstrated that the comprehensive demand results developed for SDOF systems also can be applied with confidence to low-rise MDOF systems through the use of an equivalent SDOF system.