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Probabilistic seismic demand analysis

Paolo Bazzurro
Principal Advisor: 
C. Allin Cornell
Year Published: 
Thu, 01/01/1998 (All day)
Bazzurro_Paolo1.pdf2.58 MB

This dissertation encompasses a number of issues in earthquake engineering which may appear quite diverse in nature. Several methodological aspects of both conventional and novel approaches to probabilistic seismic hazard assessment are discussed here along with subjects more strictly pertinent to structural and geotechnical engineering. This work, however, has a unique, ultimate goal: to provide procedures for an effective and practical probabilistic estimation of structural displacements due to seismic ground shaking. In modern multi-level design and rehabilitation procedures, structural performance is in fact quantified by deformation demand levels exceeded with a specified frequency per annum of structural life. We refer to this as Probabilistic Seismic Demand Analysis (PSDA).

Necessarily, this ambitious task requires one to address the problem from multiple perspectives which range from the characterization of the seismicity in the region around the site, through the evaluation of the level of ground shaking at the surface of the local soil deposit, to the computation of the resulting response of the structure subject to such a ground motion.

A unifying factor in this study is that the probability tool is consistently applied throughout all the steps. Because of the inherent randomness of earthquakes and because of the many uncertainties involved, a realistic estimation of structural behavior due to ground motions can only be attempted in a probabilistic sense. A rational approach needs to consider both the range and the relative likelihood of possible ground motion levels and the variability in soil and structural responses.

The aspects related to ground-motion characterization at the site which are investigated here include: (a) hazard disaggregation techniques, (b) a novel representation of the seismicity based on hazard contours, (c) the evaluation of ground hazard at the surface of nonlinear soil deposits with uncertain soil properties, and (d) a methodology for estimating the joint hazard for a site in terms of multiple response parameters (e.g., spectral accelerations at different oscillator frequencies). The use of these techniques is carried out in several case studies. Examples are also given on how these methodologies can be utilized towards the goal of probabilistically estimating the performance of structures located at a given site.