عنوان مقاله [English]
Lifelines are essential for human life and economic development. Buried steel pipelines are the sort of lifelines that their strength under extreme events, such as earthquakes, is very essential. One of the causes of failure of buried pipelines is seismic wave propagation. Buried steel pipelines are vulnerable in extreme events such as earthquakes. In this study vulnerability of buried steel pipelines was evaluated using the results of incremental dynamic analysis (IDA). Several IDA analyses of three buried steel pipe models with a different diameter to thickness and burial depth to diameter ratios and different soil properties, were performed using far-field earthquake ground motion records. The models were designed based on American Lifeline Alliance (ALA) guidelines. The finite-element method was used in the analyses. The buried pipeline and the surrounding soil were modeled using beam, spring, and damper elements. The peak axial compression strain at the critical section of pipe was used as an engineering demand parameter of buried pipe and peak ground velocity (PGV) was considered as a ground motion intensity measure. Then, limit states for buried pipelines were proposed and fragility curves of pipes were developed based on IDA results for the limit states. In addition, a relation for damage ratio of buried pipelines in term of axial compression strain of pipe was proposed. The results of this study show that the maximum axial compressive strain of pipeline, due to seismic wave propagation, becomes 5.7 times with doubling the PGV. It was found that the predicted number of repairs increases by a factor of about 1.87 when PGV is double. The seismic damage probability of pipeline increases with increasing natural frequency of vibration of the pipe-soil system. It seems that the ALA guidelines are not enough for seismic design of some steel buried pipelines especially the soil-pipe systems with high natural frequency. This requires a more comprehensive study.