Mechanical behavior and strength prediction of UHPC pipes under radial external loading

Ultra-high-performance concrete (UHPC), with its advantages of high strength, toughness, and durability, shows excellent applicability in drainage pipeline engineering. To investigate the radial compressive performance of UHPC pipes, four full-scale specimens were tested under radial external loading, taking steel fiber content and circumferential reinforcement ratio as key variables. Based on these experiments, numerical simulations were performed to analyze the effects of wall thickness, cover thickness, and the strengthening mechanism of UHPC. The results show that UHPC pipes exhibit high strength and good post-peak ductility, enabling the reinforcement to fully mobilize its load-bearing capacity. When the steel fiber content increased from 1.5% to 2.0%, the ultimate load increased by 22.6%; when the circumferential reinforcement ratio increased from 1.5% to 2.0%, the ultimate load increased by 15.8%. The crack load was mainly governed by the steel fiber content, while the ring stiffness was primarily determined by the reinforcement ratio. The stress softening rate at the bending-control section increased with higher steel fiber content and decreased with higher circumferential reinforcement ratio. The existing specification T/CBMF 185-2022 provided overly conservative predictions for the compressive capacity of UHPC pipes. After parameter modification, the average relative error of predicted radial compressive capacity was reduced to within 6%, significantly improving the calculation accuracy. This study provides a theoretical and practical basis for optimizing the structural design of UHPC pipes and promoting their application in pipeline engineering.