Rotation capacity of structural concrete members

A plastic rotation capacity expression based on a realistic non-linear analysis model is derived for structural concrete members. Effects of section shape, compression reinforcement and bending moment distribution are considered. A set of diagrams enables the plastic rotation capacity of rectangular, T and I structural concrete members under linear, sagging, and hogging bending moments to be determined. Use of these diagrams enables the compatibility requirement of critical sections of structural concrete continuous beams under either concentrated or distributed loads to be checked. Comparison with available plastic rotation formulations shows that neglecting the influences of the loading distribution and of ratios between contraflexure point distance and the section depth may lead to non-conservative results. It is found that for lightly reinforced sections (steel failure) plastic rotation capacities increase, while for highly reinforced sections (concrete failure) plastic rotation capacities decrease, with increasing reinforcement index values.