Modelling bond within Elasto-plastic stress fields (EPSF) models

The design of reinforced concrete includes the detailing of the reinforcement, particularly the verification of the required bars' anchorage length. For the assessment of an existing structure, the position and the detail of the rebars' anchorage are essential to verify the bond stress between concrete and reinforcement. This aspect can be critical in "D" regions, where a high bond stress demand frequently occurs.

The stress field models include such aspect in the geometry definition of the model, to appropriately assess the distribution of the stresses. Also, the models with EPSF (Elasto-Plastic Stress Field) Finite Elements are a useful tool to understand and to evaluate structures and experimental results. One primary characteristic is its explicit definition of the reinforcement with 1D Finite elements. The distribution of stresses in concrete and the forces in the steel bars is the usual output from these models. However, the steel and concrete finite elements usually share the same nodes, which implies a perfect link between the two materials. This paper briefly presents a new finite element, with zero-length dimension (0D), to be used with EPSF models, that appropriately reproduces this type of interface linking the two materials.

The FE has three nodes, one to connect to steel (1D FE) and two to connect to concrete (2D FE). The use of the two nodes to link concrete allow for the transverse pressure consideration in the bond strength.

The communication includes a validation example to check a simples anchorage length with and without transverse pressure. Application examples with beam-column joints are also presented to illustrate the differences in the force-displacement curves.