VULNERABILITY EVALUATION OF BURIED STEEL PIPELINES UNDER SEISMIC WAVE PROPAGATION

Lifelines are essential for human life and economic de-velopment. Buried steel pipelines are the sort of life-lines that their strength under extreme events, suchas earthquakes, is very essential. One of the causesof failure of buried pipelines is seismic wave propaga-tion. Buried steel pipelines are vulnerable in extremeevents such as earthquakes. In this study vulnerability ofburied steel pipelines was evaluated using the results ofincremental dynamic analysis (IDA). Several IDA anal-yses of three buried steel pipe models with a di erentdiameter to thickness and burial depth to diameter ra-tios and di erent soil properties, were performed usingfar- eld earthquake ground motion records. The mod-els were designed based on American Lifeline Alliance(ALA) guidelines. The nite-element method was usedin the analyses. The buried pipeline and the surroundingsoil were modeled using beam, spring, and damper ele-ments. The peak axial compression strain at the criticalsection of pipe was used as an engineering demand pa-rameter of buried pipe and peak ground velocity (PGV)was considered as a ground motion intensity measure.Then, limit states for buried pipelines were proposedand fragility curves of pipes were developed based onIDA results for the limit states. In addition, a rela-tion for damage ratio of buried pipelines in term of axialcompression strain of pipe was proposed. The resultsof this study show that the maximum axial compressivestrain of pipeline, due to seismic wave propagation, be-comes 5.7 times with doubling the PGV. It was foundthat the predicted number of repairs increases by a fac-tor of about 1.87 when PGV is double. The seismicdamage probability of pipeline increases with increasingnatural frequency of vibration of the pipe-soil system.It seems that the ALA guidelines are not enough forseismic design of some steel buried pipelines especiallythe soil-pipe systems with high natural frequency. Thisrequires a more comprehensive study.