Equivalent stress block to characterise force–displacement behaviour of circular RC column considering steel bond slip

The compressive zone of concrete with a circular cross-section is simplified to an equivalent rectangular stress block with a width, height and thickness of the peak concrete strength considering the confinement ratio. The shape factors of the equivalent stress block at any concrete strain level are modelled through selected equations of the ratios of the axial load and moment sustained by compressive concrete. The proposed equivalent stress block is used to predict the force–displacement behaviour of a circular, reinforced-concrete (RC) column considering steel bond slip. A comparison with the test results of column specimens indicates that the proposed equivalent stress block can predict the lateral responses with good accuracy; moreover, the variation in the strain of longitudinal rebar and the deformation ratios of flexure and steel bond slip can also be reasonably predicted. The proposed equivalent stress block can be applied widely to other concrete models; furthermore, the capacity curve of the circular RC column can be reasonably predicted by the proposed simplified piecewise model based on the equivalent stress block.