Fragility Study of Buried Pipeline Networks Based on Copula Function

The seismic fragility of water supply networks is an important research component for lifeline engineering in earthquake-prone regions. An accurate computational model was established to rapidly and efficiently assess pipeline damage under seismic excitation. In this study, the fragility of the pipeline network is deduced based on Copula function technology and the series-parallel model. This solves the low accuracy problem caused by simplifying elbow, tee, and other nodes and ignores the correlation between connected components in the fragility calculation of the buried pipeline network. Then, the shaking table tests of the elbow pipe, tee pipe, and scale pipeline network are performed, and the prototype pipeline network’s finite element comparative calculation model is also established. Then, the optimal Copula function for the pipeline network, the Gumbel Copula function, is obtained by calculating the correlation between each component’s seismic demand. It was found that the seismic demand of pipe and elbow components in the sand is higher than that in the clay, while the opposite is valid for the tee component. After that, a two-parameter log-normal distribution is employed to obtain the seismic fragility of three types of components in different soil properties. It was also found that the maximum failure probability can be obtained from the elbow leakage. The fragility of the elbow pipe is greater than that of the tee pipe. The fragility of components is then applied to the fragility calculation of the scale pipeline network by a series-parallel model, and the obtained results are compared with numerical simulations. It is demonstrated that the series-parallel combination calculation-based results have a high safety reserve for the pipeline design.

At present, urban municipal pipeline networks face many challenges in earthquake-prone regions, such as old pipeline infrastructure and poor seismic performance, which make their nodes and push-on joints vulnerable to damage. Based on the above social needs, this paper focuses on the accurate calculation theory of the seismic fragility of the buried water supply network. A more reasonable calculation method of the reliability of the pipeline network is established by considering the influence of the fragility of connected pipe components. This method employs the failure probability of various components to accurately calculate the fragility of the large and complex pipeline network. This study can provide basic theories for the seismic fragility of pipeline networks, the calculation of seismic connectivity, and the construction of resilient pipeline networks. In addition, the conclusions proposed in the study, such as the fragility comparison of tees and elbows and the design concept of “strong nodes”, can guide the design of pipeline network nodes, which has great practical significance and social benefits.