Development of Fragility Curves for Problems in Geotechnical Earthquake Engineering

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The objective of this research project is to develop fragility curves for a wide range of problems in geotechnical earthquake engineering; specifically, for foundations, slopes, and retaining walls.Fragility curves provide the probability of exceeding a prescribed damage level (e.g. minor, moderate, major, complete) for a certain type of structure, as a function of the severity of the seismic event. Fragility curves are extremely significant from the engineering applications point of view as practicing engineers can use them directly without having to perform any complex computations, and because they form the basis for all risk analysis/loss estimation/risk reduction of civil infrastructure systems. Although fragility curves have been established for structures such as buildings and bridges, there hasn't been any systematic effort to develop such curves for geotechnical structures (e.g. foundations, slopes, retaining walls). Such a task is particularly important, as damage to these structures is quite extensive during major earthquake events.Empirical fragility curves will be computed using available damage data from recent seismic events such as: the Loma Prieta, the Northridge, the Kobe, Japan, the Izmit, Turkey and the Chi-Chi, Taiwan earthquakes. In parallel with the task of establishing the empirical fragility curves, analytical fragility curves will be computed using Monte Carlo simulation techniques. One of the important tasks is to compare the "empirical" and "analytical" fragility curves so as to improve their accuracy and reliability. Several issues related to the establishment of fragility curves for such geotechnical structures will be addressed, including the definition of the different damage states for each type of structure and the measure of the intensity of the earthquake event. Different mechanisms will be considered to cause damage to the geotechnical structures considered. Particular emphasis will be given to soil liquefaction, to slope failure due to exceeding the shear strength, and to tilting of foundations and foundation systems.The establishment of fragility curves for a range of geotechnical structures will form the basis for the risk analysis/loss estimation/risk reduction of such structures, when subjected to earthquakes. These fragility curves will allow public and private organizations to make rational assessment of 1) the potential damage to civil infrastructure systems from earthquakes, 2) retrofitting strategies, 3) insurance premiums, and 4) guide emergency management teams to identify high-risk systems.This project involves a collaboration between researchers at Princeton University and the State University of New York at Buffalo.