Performance of ductile iron push-on joints rehabilitated with CIPP liner under repetitive and seismic loadings

The cured in place pipe (CIPP) liner technology is to install flexible polymeric liners with thermosetting resin inside existing pipelines. Compared with traditional methods of pipeline retrofits, CIPP provides an economic and environmentally friendly alternative for pipeline rehabilitation. However, the lack of proper constitutive models of the push-on joints and the CIPP-liner reinforced joints remains a critical deficiency in current numerical simulations of buried segmental pipelines. This paper presents new constitutive models of ductile iron (DI) push-on joints, before and after reinforced with one type of the CIPP liners, commonly used in pipeline retrofits. The proposed models were calibrated from the full-scale quasi-static tests performed on water-pressurized DI pipelines with push-on joints. These new joint models, considering strength degradation and energy dissipation of the joint, well characterizes the longitudinal behavior of the push-on joint and the liner-strengthened joints under repetitive axial loading, which primarily represents the expansion and contraction effects of the joints due to thermal effects or seismic waves traveling along the buried pipelines. Moreover, this paper also provides a rational procedure for evaluating the seismic performance of buried pipeline with different push-on joints. The proposed numerical procedure could be generally applied to quantify the seismic performance of buried straight pipelines incorporating the proposed joint models under seismic wave propagation. Numerical results indicate that the CIPP liner can significantly improve the seismic performance of the push-on joints subjected earthquake induced transient ground deformations.