Abstract:

In this work a concurrent multiscale analysis of concrete is presented, which two distinct scales are considered: the mesoscale, where the concrete is modeled as a heterogeneous material and the macroscale that treats the concrete as a homogeneous material. The mesostructure heterogeneities are idealized as three phase materials composed by the course aggregates and the mortar matrix, which are considered homogeneous materials, and the interfacial transition zone (ITZ) which is treated as the weakest phase. The course aggregates are generated from a grading curve and placed into the mortar matrix randomly. Their behavior is described by an elastic-linear constitutive model due to significant higher damage strength when compared with the other two phases of the concrete. Special continuum finite elements with high aspect ratio (ratio by the largest to the smallest dimension) with a damage constitutive model are used to describe the complex nonlinear behavior due to propagation of cracks, which is conducted by crack initiation in the ITZ and propagation to the mortar matrix until macro-crack formation. These interface elements with high aspect ratio are inserted in between all regular finite elements of the mortar matrix and in between the mortar matrix and aggregates elements representing the ITZ (see figure 1). In the limit case, when the thickness of interface elements tends to zero and consequently the aspect ratio tends to infinite, these elements present the same kinematics as the Continuous Strong Discontinuity Approach (CSDA), being suitable to represent the formation of discontinuities associated to cracks, similar to cohesive models. A tensile damage model is proposed to model nonlinear mechanical behavior of the interfaces associated to the crack formation and also to the possible crack closure. A variety of tests are performed to show the ability of the proposed method to predict the behavior of cracks initiation and propagation in the tensile region of the concrete. The numerical results are compared with the experimental ones.