Issue 29

R. Serpieri et alii, Frattura ed Integrità Strutturale, 29 (2014) 284-292; DOI: 10.3221/IGF-ESIS.29.24 291 Figure 6 : interface tangential stress vs. the distance from the loaded end for varying microplane inclination 1 3      nd comparison with experimental results in [18]. Figure 7 : interface tangential stress vs. the distance from the loaded end for varying fracture energy  cI cII G G nd comparison with experimental results in [18]. Figure 8 : vertical direct stress in the bar vs the distance from the loaded end: comparison of the simulation results with the experimental results in [18]. Figure 9 : vertical direct (total) strain in the bar vs the distance from the loaded end: comparison of the simulation results with the experimental results in [18]. C ONCLUSIONS he cohesive-zone model proposed in [9, 10], which combines elastic damage, friction and dilatancy due to mechanical interlocking, has been revisited in this paper and further validated by simulating the pull-out test conducted by Shima et el. and reported in [16], obtaining good agreement between experimental and numerical results. The relatively large dimensions of the concrete block and the clay sleeve inserted at the top of the steel-concrete interface, which moves the stress concentration well inside the block, result in negligible damage and plasticity in the concrete block. This gives more significance and robustness to the presented validation because the only significant source of nonlinearity are the concrete-steel interface interaction and the plasticity in the mild-steel bar, with values of the plastic strains in the bar exceeding the end of the plateau of the stress-strain curve of the steel. The latter aspect is also significant because it has been observed that the deformation of steel bars affects the experimentally measured bond-slip law, particularly when reaching the plastic range [16]. The main strength of the proposed model is that it effectively separates the total dissipated energy per unit of new crack surface, i.e., the measured mode-mixity dependent fracture energy, into the sum of three contributions. A first one is the rupture of bonds, which is mode-mixity independent and is therefore given by one single value of the fracture energy cI cII G G  nd, for each microplane, this translates in a single variable k D easuring the evolution of damage. A second contribution is given by the frictional dissipation that would be present even if, at the microscale, the interface presented no asperities, i.e. if it was completely flat. For the k th microplane this dissipative mechanism is related to the evolution of the inelastic slip s f k Finally, the third contribution, which has a predominant influence on the bond-slip relationship between concrete and ribbed steel bars, is given by the interlocking effect, which is here modelled through the above described multiscale approach and the definition of a pattern of microplanes in the RIA. T