Unbalanced moment resistance in slab-column joints: Analytical assessment

ACI 318-05 considers that unbalanced moment, M-u, transferred between column and slab is resisted in part (gamma M-v(u)) by shear and the remaining part, [(1-gamma(v))M-u] by flexure. The code specifies the fraction gamma(v) and permits, in Section 13.5.3.3, that the fraction can be decreased when two requirements for the shearing force, V-u, and for the flexural reinforcement ratio, rho(flex), are satisfied. Nonlinear finite-element analyses for interior, edge, and corner connections are employed to calculate the value of gamma(v) at all load stages up to failure, indicating that the gamma(v) reduction as permitted by 13.5.3.3 is not justified. This statement is supported by experimental interaction graph.