Flexural rigidity, curvature and rotation and their significance in reinforced concrete design

Some of the more fundamental and possibly less familiar aspects of current ultimate load theory are discussed, the behaviour of the simply supported under-reinforced concrete beam being used for illustration. The generalized relations between bending moment and curvature, and bending moment and rotation are given. The value of the mean flexural rigidity of the member is derived and compared with other possible values. The concept of the plastic hinge and the significance of elastic and inelastic contributions to the over-all deformation of the member are discussed.