Expressions for moment of resistance of RC structural walls

IS 456:2000 and IS 13920:2008 do not prohibit failure of RC structural walls by concrete in compression reaching the limiting strains. But, IS 13920:2008 (Annex A), which follows guidelines set by IS 456:2000, does not discuss the failure of RC walls under pure or almost pure compression of concrete in the P-M interaction curve. But, designers need the entire P-M diagram to be able to better understand the designs being proposed by them. In the determination of the ultimate moment of resistance (Ma), even when steel reaches the limiting strain first, secondary compression failure (εc=0.0035) is used as a basis (as has been customarily done in shallow RC beams and slabs) for arriving at the expressions for Mu. This is inadmissible in deep RC members, like structural walls. Tins paper presents expressions for Mu of RC walls, (1) based on basic principles of mechanics, namely equilibrium of the section, compatibility of strains and constitutive laws, (2) for all possible positions of neutral axis, and (3) without assuming secondary compression failure of RC members. Also, effect of concrete confinement by transverse reinforcement on P-M curve is presented; comparisons are presented of current method (unconfined) and proposed methods (unconfined and confined) of arriving at Mu and MΩ of RC structural walls.