CALCULATION OF THE ULTIMATE FLEXURAL CAPACITY OF NORMAL SECTION OF RC CIRCULAR COLUMNS

Numerical analysis is carried out to calculate the ultimate flexural capacity of normal section when a reinforced concrete (RC) circular column fails. The transverse reinforcement confinement and strength enhancement of longitudinal reinforcement are properly considered. It is found the calculated ultimate flexural strength is significantly larger than ideal flexural strength defined in the code, especially when the axial load ratio is high and the transverse reinforcement confinement is strong. The determination of the depth of compression zone is the key to calculate the flexural capacity of circular columns. The numerical analysis results show that the axial load ratio, transverse reinforcement characteristic value and longitudinal reinforcement characteristic value are the three main parameters which can influence the depth of compression zone. Based on the regression of the numerical analysis results, the computing formula of central angle, απ, corresponding to compression zone is established. Based on the test results of 95 larger scale columns, the formula to calculate the ultimate flexural strength is proposed, and the calculated results agree well with the test results. The results from parametric studies demonstrate that when the axial load ratio is 0.6, the ultimate flexural strength can be improved about 60% larger than that calculated from the formula provided in the code, which should be properly considered in structure design.