The role of locking segments on an earthquake-resistant segmented ductile iron water pipeline joint behavior under tension and bending

Abstract

Ground displacements by fault movements or landslides can cause significant damage and failure of buried water pipelines. This is particularly concerning for urban water distribution networks with segmented water pipelines connected by vulnerable joints. The objective of this study is to assess the deformation and failure mechanism of a ‘restrained’ axial joint integrated into a segmented ductile iron pipeline to enable it to tolerate significant ground movements. This joint type employs locking segments to restrain the relative axial movements of the two pipe sections after some free movement. The hypothesis of this study is that the joint structure and locking segment orientation influence the joint’s performance. A series of full-scale axial and bending tests were conducted on an 8-inch (203-mm) diameter jointed ductile iron pipeline with various orientations of the locking segments at the joint. Distributed fiber optic sensor (DFOS) was utilized to capture the development of spatially continuous strain profiles of the joint section and the pipes with increasing loads. Three-dimensional (3D) finite element (FE) models of the jointed pipeline are developed and validated against the DFOS measurements. Combined results from the laboratory tests and FE analyses show that the behavior of joint opening under increasing tension has three stages, depending on the interaction between the spigot and the locking segments. In particular, the axial force builds up significantly when the weld bead starts to engage with the locking segments until it breaks. A crack initiates at the interface between the locking segment and single slot. The joint behavior observed by the four-point bending tests can be also divided into three distinctive stages, and each of them influenced by the orientations of the locking segments in terms of deflection flexibility, capacity, and the initiation deflection points for potential joint failure and water leakage. The effect of the initial positioning of the bell-spigot joint on the joint’s overall bending stiffness is investigated. In addition, a novel joint bushing connector model is proposed as a surrogate model of the continuum contact model of the bell-spigot joint. This bushing connector model is capable of capturing the essential characteristics of the joint while simultaneously mitigating computational time for future modelling of pipeline system in system level.