Stress analysis of steel fiber reinforced concrete encased tubular steel penstocks under internal water pressure

Reinforced concrete encased steel penstocks (RC-ESPs), which are usually laid on the downstream surfaces of dams, have been applied in many large hydraulic projects including the famous "The Three Gorge Project" of the Chinese mainland. Compared to conventional steel penstocks, which are usually embedded in dams, RC-ESPs are easier to construct, cost-effective and more safe and durable. However, a difficulty encountered in engineering practice for such a composite structure is in the crack control of the exterior reinforced concrete (RC) wall. To solve such a problem, steel fiber reinforced concrete (SFRC) can be used to replace the conventional concrete of the external RC wall to form a new type of structure: steel fiber reinforced concrete encased steel penstocks (SFRC-ESPs). The objective of this paper is to develop generic analytical models for analyzing the SFRC encased tubular steel penstocks (SFRC-ETSPs) under internal water pressure. A tri-linear curve is assumed in the models to describe the behavior of SFRC under tension. Based upon the developed models the strains and stresses of all the structural components, including the encased steel penstock and the steel reinforcement and SFRC in the exterior RC wall, can be predicted under different levels of internal water pressure. The analytical models provide a sound basis for designing the serviceability and safety of the SFRC-ETSPs.