The nonlinear mechanical behaviour of pipeline joints influences the seismic response of water supply pipelines. This study presents an experimental investigation of the tensile behaviour of push-on joints of ductile iron (DI) pipelines, subjected to axial tensile forces and internal water pressure. The axial performance and damage states of joints are determined for push-on joints with different diameters. A statistical analysis is then conducted to determine the correlation between tensile strength and joint opening. An empirical equation for estimating the tensile strength of pipeline joints is proposed, along with a normalized failure criterion for joint opening considering water leakage. Moreover, a numerical model for buried pipelines considering nonlinear soil-pipe interaction is developed. Incremental dynamic analysis (IDA) is performed on DI pipelines with explicit consideration of the uncertainty of joint mechanical properties. Seismic fragility curves are developed based on the IDA results. The effect of mechanical parameter uncertainty of pipeline joints on seismic risk assessment of segmented pipelines is quantitatively evaluated. The numerical results indicated that the failure probability of the pipeline considering the uncertainty of joint mechanical properties is approximately 1.5 to 2 times larger than that predicted by a deterministic model.

Safety assessment of ductile iron (DI) pipelines under fault rupture is a crucial aspect for underground pipeline design. Previous studies delved into the response of DI pipelines to strike-slip faults, but all existing theoretical methods for DI pipelines under strike-slip faults are not suitable for normal fault conditions due to the difference in soil resistance distribution. In this study, analytical solutions considering asymmetric soil resistance and pipe deflection are developed to analyze the behavior of DI pipelines under normal faulting. Results indicate that DI pipelines with a longer segment length are more vulnerable to pipe bending damage, while exhibiting a lower sensitivity to joint rotation failure. For the conditions of pipe segment length L = 1.5 m at all burial depths and L = 3 m at a shallow burial depth, when the fault-pipe crossing position shifts from a joint to a quarter of the segment length (rp = 0 similar to 0.25), DI pipelines are more prone to joint rotation failure. However, in the cases of L = 3 m at a moderate to deep burial depth and L = 6 m at all burial depths, the most unfavorable position is rp = 0.75, dominated by the mode of pipe bending failure.