Long-term ring stiffness of fiberglass-reinforced plastic mortar pipes

Fiberglass-reinforced plastic mortar (FRPM) pipes are lightweight, high-strength, and corrosion resistant. Owing to several additional advantages including the ability to convey large flows, convenient installation, and low overall costs, FRPM pipes are well-suited to various pipeline systems in the chemical, water, and drainage industries. As a polymer matrix composite material, the mechanical properties of FRPM pipes are time-dependent. Ring stiffness measures the ability of a pipe to resist deformation under an external load and decreases with increasing service time. Reduced ring stiffness can lead to excessive deformation, which can affect the long-term durability of the pipeline, eventually resulting in failure. At present, only few studies have been conducted on long-term ring stiffness of FRPM pipelines, which has hindered their application. In this study, long-term ring stiffness of 500 mm diameter pipes comprised of FRPM was tested under two different loading conditions: constant load and constant displacement. Variation of ring stiffness with time under constant load and constant displacement conditions was obtained and the predicted attenuation of ring stiffness after 50 years was found to be 11.62 % and 15.48 %, respectively, which further confirms the reliability of long-term ring stiffness predictions based on short-term test data. And the results will contribute to further studies on the long-term ring stiffness of FRPM pipes.