Three-dimensional modeling of concrete structures .1. Plain concrete

A triaxial constitutive model for finite-element (FE) analysis of pre-and postcracking behavior of concrete is presented. A five-parameter ultimate strength envelope is used in the stress space. For compression dominated loading leading to crushing, a modified version of a conceptually simple hypoelastic model is used and augmented to capture the postcrushing strain softening behavior approximately. Various test data on multiaxial loading of concrete are analyzed to verify the capabilities of the model. The postcracking strain softening formulation is based on the fracture energy concept with multiple nonorthogonal crack capability. To maintain the objectivity with respect to mesh refinement, a simple method is proposed to compute the crack band widths within 20-noded solid isoparametric elements. This model is verified by analyzing the postcracking response of a uniaxial tensile member, a test notched beam, and a beam subjected to torsion.