Modelling Structural Concrete with Strut-and-Tie Model Combined with 2D Finite Elements - A Model Factor for the Assessment of Strut-and-Tie Models

Despite being a widely used structural material, the deep knowledge on behaviour of structural concrete represents a continuous challenge to the technical community. The definition of local and global interactions between materials, the accurate definition of its geometry, supports and loads are basic requirements to establish adequate models to understand the mechanical behaviour of such structural elements. One important tool is the strut-and-tie models (STM) that are simple for the structural engineering because they link analysis, design, and detailing. A fundamental advantage of STM is their versatility: they can be used in several stages of project. The STM makes the interpretation of structural concrete internal forces more intuitive. However, the computation of deformations based on these models is not a trivial task. In this paper, the authors present a new method that uses the forces of STM to compute deformations in a continuum media (FEM approach). This method keeps the fundamental feature of STM, evaluation of equilibrium, and allows to model deformations realistically, since they are explicitly computed in a 2D model. In this proposed method, hereinafter denoted STM/2D, these (1D and 2D) models are linked throughout a variational principle, using the so-called “three-fields” technique. A model factor (M-Factor) that compares the behaviour of STM with 2D model is proposed. Illustrative examples are presented for typical problems. Different STM for the same problem are compared based on the proposed factor.