Probabilistic Simulation-Based Evaluation of the Effect of Near-Field Spatially Varying Ground Motions on Distributed Infrastructure Systems
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Authors
Taslimi, Arsam
Issue Date
2024
Type
Dissertation
Language
Keywords
Corrosion Effect , Fully Probabilistic Seismic Assessment , Long-span Bridge , Material Uncertainty , Physics-based Simulated Ground Motion , Spatially Variable Vertical Ground Motions
Alternative Title
Abstract
This research has developed a probabilistic simulation-based framework integrating hazard-consistent ground motion aleatory variability and uncertainties associated with material properties and aging. The goal is to enable the estimate of the impact of site-specific, spatially variable ground motions on the nonlinear seismic response of long-span transportation systems as opposed to records from worldwide catalogs when following code-compliant approaches for structural design. A bridge representative of the pre-retrofit San Francisco-Oakland West Bay Bridge and a suite of validated realizations of an M7 Hayward fault strike-slip earthquake in the San Francisco Bay Area are utilized as a case study. Findings indicate that the median and variability of the demands posed by the simulated motions and the real records scaled to the same site-specific spectra are markedly different. Assessments performed on the single bridge components under different loading scenarios highlight the sensitivity of complex structures to multiple characteristics of the ground motions that might be biased by current scaling methods, thus providing the basis to inform current ground-motion selection and scaling procedures. It was also found that the incorporation of material uncertainties, including the effect of aging and corrosion, meaningfully affects median responses, yet leaving the dispersion primarily controlled by the aleatory variability associated with the selected set of motions. The least effects of material uncertainty and aging are seen for those elements in which there is a competing effect of change in the dynamic characteristics and concordant variation in the ground-motion intensities (spectral shapes). By leveraging the availability of suites of three-component, site-specific ground motions, the impact of spatial variability was isolated and quantified. It was demonstrated that ground-motion site-to-site variability has the largest influence on the response of the bridge decks in the vertical direction. Analyses in the time and frequency domain determined that this derives from the excitation of higher modes and changes in the modal contribution caused by the out-of-phase deformations of the bridge components and the phase lag of the input motions deriving from even limited spatial variability. This research has provided the computational and methodological framework for conducting site-specific probabilistic assessments of distributed infrastructure that can be utilized with different systems and updated as more ground motions from new scenarios become available.