Characterization of Strong Ground Motions for Performance Based Seismic Engineering

Abstract

Given the uncertainty in the timing, location and magnitude of future earthquakes, for most engineering purposes it is most meaningful to use a probabilistic approach to characterizing the ground motion that a given site will experience in the future. A probabilistic seismic hazard analysis takes into account the ground motions from the full range of earthquake magnitudes that can occur on each fault or source zone that can affect the site. The probabilistic approach is very compatible with current trends in earthquake engineering and the development of building codes, which have embraced the concept of performance based design. In contrast to the traditional building code approach, performance-based design requires an explicit prediction of the structure's performance at each of several ground motion levels corresponding to a set of performance objectives. Each performance objective is associated with an annual probability of occurrence, with increasingly undesirable performance characteristics caused by increasing levels of strong ground motion having decreasing annual probability of occurrence. Performance based design requires a more comprehensive representation of ground motions than has conventionally been used. For example, ground motions estimates are needed at multiple annual probability levels, and may need to be specified not only by response spectra but also by suites of strong motion time histories for input into time-domain non-linear analyses of structures, because response spectrum analysis is based on a linear elastic model and therefore does not address the non-linear response that is the essence of building damage and failure.