The plastic flow law for reinforced concrete beams under combined flexure and torsion

Synopsis The possible application of plastic analysis to reinforced concrete structures, the members of which are subjected to both bending and twisting moments, depends not only upon their ductility but also upon a knowledge of the associated plastic flow law. An experimental investigation to determine the flow law for rectangular reinforced concrete beams under combined flexure and torsion is described in this paper. Bending and twisting rotations measured during the pseudo-plastic stage occurring near maximum load are reported for 80 beams, which included both symmetrically and unsymmetrically placed reinforcement. Typical interaction curves with their associated incremental rotation vectors are presented and the corresponding flow law is stated. The complete interaction curve is considered and the implications of this and the plastic flow law are discussed in relation to the applicability of current methods of plastic analysis to concrete structures.