Nonlinear model for reinforced concrete slabs and discs

Four main finite element models have been developed for reinforced concrete slabs: 1. Modified stiffness method models that include the nonlinear variation of material properties through the depth of the slab. 2. Layered models, made up of a series of plain stress layers. 3. Space element modelling in which a certain number of Gauss points are used for integration through the thickness. 4. Models based on slab analysis in which the cracks are treated as lines of discontinuity of rotation angles. Effect of such cracks is transmitted to the nodes. An intermediate approach between the first two methods is proposed. It is attempted to model nonlinear concrete behaviour (including cracking), steel reinforcement deformation in elastic-plastic range as well as coupling between extension and flexure. By virtue of using certain cracking modes the approach implies a division of a slab into a few layers and leads to a simple form of constitutive matrix of the slab. (orig./HP)