CONSTITUTIVE MODEL FOR ENGINEERED CEMENTITIOUS COMPOSITES UNDER BIAXIAL COMPRESSION

Based on the Darwin-Pecknold method considering the biaxial behavior of concrete, a two-dimensional constitutive model for engineered cementitious composites (ECC) is developed, taking into account the nonlinear mechanical behavior and the variation of compressive strength under biaxial compression. A nonlinear stress-equivalent uniaxial strain relationship is established after introducing the equivalent uniaxial strain in two orthotropic directions caused by biaxial loading to account for the biaxial nonlinear behavior of ECC. A biaxial strength envelope is used to determine the compressive strengths of the two directions. An explicit numerical algorithm of the model is derived, and user-defined material subroutine UMAT containing the numerical algorithm is coded and implemented in finite element procedure ABAQUS v6.14. The efficiency of the proposed model is validated through numerical simulations of two sets of ECC specimens with different mix proportions under biaxial compression loading at various biaxial stress ratios. The stress-strain curves and the compressive strengths in the major compressive stress direction obtained by numerical simulations are in a good agreement with the experimental results. It is shown that the proposed constitutive model can effectively predict the biaxial nonlinear mechanical behavior and the failure strengths of ECC under biaxial compression.