Disturbed stress field model for reinforced concrete: Implementation

The Disturbed Stress Field Model is a smeared delayed-rotating-crack model, proposed recently as an alternative to fully fixed or fully rotating crack models, for representing the behavior of cracked reinforced concrete. It is an extension of the modified compression field theory; advancements relate to the inclusion of crack shear slip in the element compatibility relations, the decoupling of principal stress and principal strain directions, and a revised look at compression softening and tension stiffening mechanisms. In this paper, a procedure is described for implementing the formulations of the Disturbed Stress Field Model into a nonlinear finite-element algorithm. The procedure is based on a total-load secant-stiffness approach, wherein the crack slip displacements are treated as offset strains. Computational aspects of the formulation are shown to be simple and numerically robust. The hybrid crack slip formulation used is found to accurately model the divergence of stress and strain directions, providing an improved representation of behavior. Predictions of shear strength and failure mode are significantly influenced in some cases.