Development of fragility functions for natural gas transmission pipelines at anchor block interface

In this paper, fragility functions are developed for natural gas transmission pipelines at anchor block interface under the effect of seismic wave propagation. The fragility functions are developed for three typical pipelines in two types of soils. Seismic response of the pipeline at anchor block interface is evaluated by conducting non-linear dynamic response analysis of the pipeline system. The pipeline system consisting of the pipe, the anchor block, and the surrounding soil is subjected to ground shakings associated with a set of 36 earthquake records to develop the fragility function. The results of analyses indicate that the critical pipeline section is at pipe-anchor block interface where the pipe is susceptible to local buckling failure. The fragility functions are developed using strain limit state associated with local buckling of the pipe. The results of this study indicate that the vulnerability of pipelines to the local buckling failure at pipe-anchor block interface increases with increasing pipe diameter. Also because of the relatively large anchor blocks in soft soils, pipelines are more vulnerable to the local buckling failure in soft soils than in hard soils.