Structural behaviour of prestressed concrete beams with high-strength stirrups

Many studies related to high-strength concrete material have been conducted, but relatively few studies have considered high-strength steel reinforcement. Four current design codes - ACI 318-14, Eurocode 2, CSA A23.3-04, and JSCE-07 - limit the yield strength of transverse reinforcement to control diagonal crack width, and to ensure yielding of transverse reinforcement prior to brittle failure mode. ACI, Eurocode 2 and CSA A23.3-04 limit the yield strength of transverse reinforcement to 420, 600, and 500MPa, respectively; while JSCE-07 limits the yield strength to 800MPa, when the compressive strength of concrete is higher than 60MPa. The implementation of high-strength transverse reinforcement in prestressed concrete (PSC) and reinforced concrete (RC) beams has been determined in this study. A total of 16 beams were strengthened using higher yield strength stirrups than the code limitations, and were monotonically loaded to failure. All the beams were designed to experience shear failure prior to flexural failure. Most of the test results showed yielding of the stirrups, and narrower crack width than the code limitations even though the specimens were strengthened with higher than 420MPa stirrups. The test results imply the feasibility of using high-strength stirrups for PSC beams with regard to serviceability.