Time-dependent Seismic Fragility Analysis of Buried Steel Pipes in Alkaline and Near-Neutral Soil Environments

Abstract

In alkaline and near-neutral soil environments, the mechanical and seismic performance of buried steel pipes degrades with deepening corrosion over time. To study the seismic fragility of buried steel pipes of different service ages in these environments, an incremental dynamic time history analysis of typical pipes was carried out with the time-varying constitutive model of steel. A probabilistic seismic demand model for buried steel pipes of different service ages in alkaline and near-neutral soil environments was then established, which can characterize the probability relationship between the ground motion intensity and structural response. Furthermore, on the basis of the tristate criteria, the limits of each ultimate failure state were determined. Time-varying seismic analytical fragility models of the pipes, including pipe units in two different soil environments and four service ages, were then established, which can characterize the probability of different failure states of structures under different earthquakes. The corresponding seismic fragility curves were then drawn. Seismic fragility curves were also obtained under three different diameter ranges based on seismic damage statistics. Results showed that, under the same ground motion, with increasing service time and decreasing pipe diameter, the probabilities of three failure states, namely, basically intact, moderately damaged, and severely damaged, all increased.