Mesomechanical analysis of concrete under loading that generates rotation of cracking XIII International Conference on Computational Plasticity. Fundamentals and Applications COMPLAS XIII E. Oñate, D.R.J. Owen, D. Peric and M. Chiumenti (Eds) MESOMECHANICAL ANALYSIS OF CONCRETE UNDER LOADING THAT GENERATES ROTATION OF CRACKING L. PUIGGRÓS * , C.M. LÓPEZ * M. RODRÍGUEZ * AND I. CAROL * * Department of Geotechnical Engineering and Geo-Sciences Universidad Politécnica de Cataluña Jordi Girona 1, Edif. D2, E-08034 Barcelona, Spain e-mail: luispuiggros@gmail.com, carlos.maria.lopez@upc.edu, mariana.rodriguez@upc.edu,ignacio.carol@upc.edu Key words: Fracture in concrete, Mesomechanical analysis, Interface elements. Abstract. Willam´s test has been often used to compare constitutive models which take into account induced anisotropy due to damage and cracking. This numerical test emulates the continuous rotation of the principal stress and deformation directions, with secondary cracks forming at inclined directions while original primary cracks aligned with the axes tend to close. However, a realistic verification of this type of behavior is limited by the absence of experimental results in the literature of concrete and other quasi brittle materials, which can be explained in part due to the complexity of practical difficulties in this kind of lab test. As a first way to cover this gap, this paper presents numerical results of a concrete meso-structural model under imposed deformations at the boundary similar to the Willam’s test. The results presented include the evolution of average stress components over the sample, cracking state, etc. Generally speaking, the results obtained agree well with the predictions of advanced continuum-type anisotropic models, although some specific aspects are pointed out that would deserve further detailed study and discussion. 1 INTRODUCTION One of the advantages of numerical models is that they allow us to replace or supplement costly experimental tests. However, numerical models need validation, and for some complex aspects on the behavior of concrete and other quasi-brittle materials, at present there are not experimental tests available to compare with. This is the case in general for loading cases implying rotation of principal stresses inside the material, which are precisely crucial to fit some macroscopic models used in structural analysis. In particular, Willam et. al. [1] proposes a theoretical test in which the imposed loading process leads to a continuous rotation of the strain and stress principal direction. This test has been extensively used to check and compare different cracking and damage models [2-5], and it consists of a 2D square specimen in plane stress condition subject to the following two-step loading history under displacement control on all boundaries (Fig. 1): - During the first step, uniaxial tension is applied along x-axis until σ 1 = σ N = σ y = f’ t , that is, until tensile cracking just initiates. The lateral strain is given by the Poisson’s coefficient during this step, i.e. in the ratio: Δε xx :Δε yy :Δε xy = 1: -ν : 0. 1043