Mechanical response of FRP liner-reinforced ductile iron pipe joints under normal faulting

• A 3D FE model of FRP-reinforced DI pipe with push-on joints is established. • The model is evaluated by test results. • The impact of some variables on the results is analyzed. • The failure mechanism of FRP liner-reinforced ductile iron pipe joints is obtained. The push-on joint of ductile iron (DI) pipes represents a critical vulnerability in water supply networks traversing active faults. To evaluate the structural synergy of utilizing Fiber Reinforced Polymer (FRP) liners for pipeline rehabilitation, this study developed a three-dimensional nonlinear finite element model to systematically investigate the complex pipe-soil-liner interactions under normal fault displacements. The results reveal a highly asymmetric failure pattern where longitudinal tensile rupture at the pipe crown of the joint on the up-thrown side constitutes the governing failure mode, fundamentally contrasting with the compressive load-transfer state on the down-thrown side. Furthermore, while deep burial and high soil density effectively restrict joint rotation, they induce severe internal stress accumulation through a forced constraint mechanism. Notably, parametric analyses demonstrate that increasing the liner elastic modulus from 10 GPa to 30 GPa triggers a substantial 76% amplification in peak tensile stress, thereby exacerbating the risk of brittle fracture. Conversely, increasing the liner wall thickness from 3 mm to 7 mm strategically leverages the geometric advantage of the section modulus, achieving the dual benefit of restricting joint deformation and reducing the cross-sectional peak stress by 32.1%.