Reliability-based seismic evaluation of buried pipelines subjected to earthquake-induced transient ground motions

In this research the effect of diameter to thickness of pipe ratio (D/t), depth of burial to diameter (H/D) ratio, conditions of surrounding soil and different grades of steel on the seismic answer of straight buried steel pipelines is investigated within a probabilistic context. The results of incremental dynamic analysis of 15 pipeline models are used to evaluate the capacities of performance limit, the mean annual frequency (MAF) of exceeding structural limit states and levels of confidence of achieving seismic performance goals. It is obtained that for the pipes with the ratios of D/t over 39.9, increasing the ratio of D/t decreases the IM capacity, increases MAF of exceeding the performance objectives and reduces the confidence level of the pipes for meeting the performance objectives. It is found that increasing H/D ratio, increases MAF of exceeding the performance objectives by about 2.4 times. It is concluded that the D/t ratio of the pipelines has the most influence on the probabilistic seismic response assessment of the structures. The results show that using pipes with small D/t, soils with low Gs values, pipes with high steel grade, and reducing the burial depth of the pipelines, enhances their seismic performance.