You are hereDirect probabilistic seismic analysis: Implementing non-linear dynamic assessments

Direct probabilistic seismic analysis: Implementing non-linear dynamic assessments


Author: 
Fatemeh Jalayer
Principal Advisor: 
C. Allin Cornell
Year Published: 
Wed, 01/01/2003 (All day)
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A formal probabilistic framework for seismic assessment of a structural system can be built around the expression for the probability of exceeding a limit state capacity, a measure of the reliability of system under seismic excitations. Common probabilistic tools are implemented in order to derive a simplified closed-form expression for the probability of exceeding a limit state capacity. This closed-from expression is particularly useful for seismic assessment and design of structures, taking into account the uncertainty in the generic variables, structural "demand" and "capacity" as well as the uncertainty in seismic excitations.

This framework implements non linear dynamic analysis procedures in order to estimate variability in the response of the structure ("demand") to seismic excitations. Alternative methods for designing a program of nonlinear analyses and for applying the results of dynamic analysis, particularly as it relates to displacement-based "demand" and "capacity" estimation, are discussed. These alternative methods are presented through a comprehensive case study of an existing 7-story moment-resisting frame structure in Los Angeles. This structure represents an older reinforced concrete structure with degrading behavior in nonlinear range.

The onset of global dynamic instability in the structure is used to define the system "capacity" in this study. The probabilistic model describing the structural demand in the vicinity of system capacity is modified in order to explicitly account for the large displacement demands particular to a system close to the onset of global instability. This leads to an alternative presentation of the probabilistic framework in the range of global instability in the structure.

Ground motion record selection is potentially significant in implementing a program of nonlinear dynamic analyses. However, it is demonstrated that even under the most extreme cases, namely structures with very short and very long first-mode periods, the structural response is conditionally statistically independent of the ground motion characteristics such as magnitude and source to site distance for a given seismic intensity level. This conclusion may justify "random" record selection taking into consideration the site's soil condition and its position with respect to the major faults around it.