Issue 31

H.F.S.G. Pereira et alii, Frattura ed Integrità Strutturale, 31 (2015) 54-66; DOI: 10.3221/IGF-ESIS.31.05 64 The abovementioned differences observed between the numerical results and experimental results could be ascribed to several factors. First of all, note that the geometric representation of the ribs was approximate, since the actual ribs geometry is quite complex and its disposition along the rebar’s surface is non uniform. Therefore for modelling accurately the ribs geometry a more complex and full 3D geometrical model should be developed, in which the axisymmetric stress state cannot be considered. As previously stated the numerical responses with the discretization of the ribs were stiffer than the experimental pullout behaviour. To the latter fact may contributed the disposition of the interface elements along the lateral inclined faces of the ribs, which are not submitted to a pure fracture mode II, since they are also subjected to compressive stresses that will increase the confinement level. This aspect may contributed to an increase of the response stiffness. On the other hand, the steeper softening decay observed in the numerical curves may be related to adopted geometry of the ribs within the numerical model. In the numerical model, the start of the softening stage, after the peak load, coincides with the plastification of the compressive bulk wedges formed in front of the ribs during the pullout procedure, and the increase of the relative displacement between ribs and the surrounding concrete. Nominal Stress Normal-only Mode [MPa] Nominal Stress First Direction [MPa] Nominal Stress Second Direction [MPa] 0 0.63 0 Table 8 : Nominal stress. Figure 19 : Numerical simulation of the experimental pullout curves (rebars with ribs). C ONCLUSIONS ith the aim of studying the bond behaviour between galvanized rebars and concrete in pullout tests, distinct numerical simulations were carried out using the finite element method framework. A parametric study of the main numerical variables was performed, also to calibrate the model. The numerical simulations of the pullout tests carried out by [31] were compared with both the experimental results and the simulations with an analytical shear-lag model. Using the same bond stress – slip relationships the results obtained by the finite element method rendered a higher stiffness and maximum pullout load when compared to ones obtained with the analytical model by [31]. The pullout tests were successfully modelled assuming the steel rebar as smooth, as long a proper local bond stress – slip law is adopted. The numerical simulations including in the geometric model the rebar ribbings, at this stage dis not render so good results and further research should be carried out. The differences observed between the numerical results and experimental results when the ribs were modelled, could be ascribed to the approximate geometric representation of the ribs. Therefore for modelling accurately the ribs geometry a more complex and full 3D geometrical model should be developed, in which the axisymmetric stress state cannot be considered. Moreover, since some interface elements were not subjected to a pure fracture mode II, they may also contribute to a stiffening of the initial numerical pullout response. R EFERENCES [1] Considère, M., Influence des armatures métalliques sur les proprietes des mortiers e bétons, Le Béton Armé, 9 (1899). W