Shear truss analogy for concrete members of solid and hollow circular cross section

Solid circular columns are very popular for bridge pier design, due to simplicity of construction and because its strength characteristics under wind and seismic loads are similar in any direction. Circular elements are also used extensively as columns in buildings or as piles for foundations. Hollow core circular concrete members are much less structurally used than solid circular cross sections. However, these can be found in concrete chimneys, concrete pipes and elevated water tanks, as well as in large bridge columns and offshore platforms. Codes do not usually propose specific formulations for evaluating the shear strength of such structural types or if they do, they do so in a very simplified manner. an analytical model for evaluating the contribution of the transverse reinforcement in concrete members of solid and hollow circular cross section is presented in this paper. After a thorough bibliographic research on the previous studies on the matter, the shortage of work accomplished on the topic has been assessed and the unsolved problems identified. As far as the authors are aware, an accurate formula for evaluating the shear transferred by spiral reinforcement in solid members is presented for the first time. An accurate formula for the calculation of hollow core circular columns with both vertical and spiral reinforcement is also deduced for the first time, leading to innovative results. Assumptions made for the calculation of this formulation have been deduced theoretically, and then checked empirically. Hence, shear tests on circular hollow core specimens are also presented. A practical efficiency factor of circular and spiral shear reinforcement for solid and hollow core circular concrete members to be used for design purposes is also presented.