N-M-V interaction domains for box and I-shaped reinforced concrete members

This paper proposes an approximate physical model to evaluate the N-M-V interaction resistance domains for box and I-shaped concrete cross sections. The model subdivides the concrete beam in layers, with nearly constant stress fields, and determines the internal forces satisfying equilibrium of the cross section, applying the static theorem of plasticity (lower bound theorem). The resisting contribution of the web longitudinal reinforcements is also considered by including stress fields of variable inclination on the longitudinal element direction. The proposed model leads to a conservative evaluation of bearing capacity and permits to numerically obtain the N-M-V interaction resistance domains of the indicated cross sections. The obtained N-M-V failure surfaces are in good agreement with the experimental evidences of tests performed by P. Regan and H. Rezai-Jorabi and by J. R. Robinson and J. M. Demorieux.