Shear strength of heavily reinforced concrete members with circular cross section

Reinforced concrete members with circular cross section are used frequently in practice. Despite this fact, only limited research on the shear behaviour of such structural members has been published. Further, code rules and guidelines for shear design of circular concrete members are almost non-existent. Most code rules are based on shear models for rectangular members. The shear behaviour of circular members is, however, quite different from that of rectangular members. The difference is especially pronounced for members containing high shear reinforcement percentages. This paper presents the results of a test series on heavily shear reinforced circular concrete members. The specimens had shear reinforcement percentages up to more than three times the maximum percentage found in existing tests. The test results indicate that it is possible to obtain shear strengths which exceed the upper limit usually imposed on rectangular members. The test results are compared with a recently developed plasticity-based shear model for circular members. Satisfactory agreement was found. Comparisons were also made with calculations using the AASHTO LRFD design code. It was found that the AASHTO LRFD design code gives reasonable results for members with small amounts of shear reinforcement while it underestimates the shear strength for heavily shear reinforced members.