A composite plasticity model for concrete

composite yield function is used to describe the behavior of plain and reinforced concrete in biaxial stress under monotonic loading conditions. A Rankine yield criterion is used to monitor the in-plane tensile stresses and a Drucker-Prager yield function controls the compressive stresses. A good agreement with experimental data for biaxial stress conditions in concrete can thus be obtained. The approach is particularly powerful for the numerical analysis of concrete structures, either plain or reinforced, which are predominantly in tension-compression biaxial stress states. Initiation of cracking in such areas frequently leads to brittle, uncontrollable failure (splitting cracks), which can often not be handled by existing approaches. The proposed Euler backward algorithm basecl on the composite yield function and enhanced by a consistent linearization of the integrated stress-strain relation for use within a Newton-Raphson method at the structural level, is extremely robust for this particular class of problems