Proposal of a complete seismic shear strength model for circular concrete columns

• Proposed a complete seismic shear strength versus drift ratio relation for circular concrete columns.
• Correlated seismic shear strength with drift ratio, a direct indicator of damage.
• Improved the understanding of shear strength degradation mechanism.
• Enhanced accuracy of the evaluation of seismic shear strength.
• Provided a concise and design-oriented shear strength model.

A complete shear strength model is proposed to define the relationship between seismic shear strength and lateral drift ratio of circular concrete columns. The proposed bi-linear model comprises the initial shear strength branch and the shear strength degradation branch, and it can trace the degradation of shear strength along with lateral deformation. The formula to assess the initial shear strength is derived from the equilibrium of the forces acting on the primary shear failure plane and Mohr–Coulomb failure criteria for concrete, while the degradation slope of shear strength is associated with a factor indirectly representing the contribution by the so-called dowel action of longitudinal reinforcements. Another feature of the proposed model is that it can be used to directly calculate the seismic shear strength of circular columns without transforming circular section into an equivalent rectangular or square section. In order to calibrate the proposed model and verify its reliability and accuracy, eighty-eight relatively large scale circular concrete columns that many researchers have reported failing in shear are collected. These previous tests cover a wide range of structural factors such as concrete strength, axial load ratio, yield strength and amount of transverse as well as longitudinal reinforcements, and shear span ratio. Comparisons between the experimental results and the calculated ones indicate that the proposed model can predict the seismic shear strength and trace the shear strength degradation till large deformation more accurately than previous models.