Extended cracked membrane model for the analysis of RC panels

A new model considering fixed and interlocked cracks for the analysis of reinforced concrete (RC) cracked membrane elements is presented. The model can be regarded as an extension of the cracked membrane model proposed by Kaufmann and Marti. Its value lies in eliminating the need to resort to empirical averaged stress–strain relations for the reinforced concrete material, while being sufficiently simple for implementation in a robust finite element formulation. Equilibrium is formulated in terms of stresses at the cracks, enabling the use of fundamental theoretical models for the individual mechanical phenomena governing shear behaviour, such as concrete compression softening, aggregate interlock (including crack dilatancy effects) and tensile bridging stresses. Reinforcement stresses at the cracks are obtained from the average strains assuming a stepped rigid plastic bond shear stress–slip law according to the tension chord model. This allows for a consistent treatment of the tension stiffening effects and a proper evaluation of steel deformation capacity in the post-yielding stage. A rational and quantitative description of the stress/strain fields both at the cracks and in between the cracks is derived, which allows a deeper understanding of the complex mechanics involved in shear behaviour of cracked membrane elements. A validation campaign was undertaken using a database with the experimental results of 54 RC panels subjected to in-plane shear and axial stresses. The failure modes, failure loads and stress–strain curves are, in general, accurately predicted.