A SIMPLIFIED METHOD FOR NEAR-SOURCE PROBABILISTIC SEISMIC DEMAND ANALYSIS

Abstract eng:
Simplified computational tools for the seismic analysis of structures are often used within the framework of performance-based earthquake engineering. Substitution of a complex structural model with an equivalent single-degree of freedom (ESDoF) system is particularly popular in this context; rigorous probabilistic seismic demand analysis (PSDA) can become computationally very intensive and thus such ESDoF-based simplifications (e.g., nonlinear static procedures) that offer a first approximation reference point are more than welcome. In recent years, there has been increased interest in improving the accuracy of PSDA at sites situated in the immediate vicinity of seismic sources, also said to be under near-source (NS) conditions. One of the chief reasons behind this is the occasional emergence of NS ground motions that carry coherent impulsive waveforms, most noticeable in the velocity time-history. Such pulse-like ground motions have been shown to exhibit peculiar inelastic demands, which often supersede those of ordinary, non-impulsive motions. The methodology employed in the present study uses a recently proposed, pulse-like seismic demand model that comes in the form of analytical equations for incremental dynamic analysis fractile curves that take pulse period into account. This model is applicable for SDoF systems with multi-linear backbone curves (including a softening branch) exhibiting moderately pinching hysteretic behavior. Disaggregation of NS probabilistic seismic hazard analysis is used to provide the probabilistic distribution of pulse period at each level of seismic intensity; this site-specific information can be combined with the aforementioned pulse-like seismic demand model to perform simplified NS-PSDA at the SDoF level.

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