Issue 31

H.F.S.G. Pereira et alii, Frattura ed Integrità Strutturale, 31 (2015) 54-66; DOI: 10.3221/IGF-ESIS.31.05 63 Numerical results of the specimens with galvanized steel rebars are presented in Fig. 17. The numerical results are also inside of experimental envelope, except in initial zone of slip, were the simulations results by ABAQUS are a little outside of envelope. In terms of stiffness and maximum pullout force, the conclusions are similar to obtained with the non-alloy rebars. The response of ABAQUS has an initial peak of the pullout force followed by a softening, afterwards it was observed an increase of the pullout force. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 10 20 30 40 50 60 70 80 Envelope (Non-alloy rebars) Numerical Model (Abaqus) Analytical Model (Sena et al., 2009) Pullout Force [kN] Free end slip [mm] 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 10 20 30 40 50 60 70 80 Envelope (Galvanized) Numerical Model (Abaqus) Analytical Model (Sena et al., 2009) Pullout Force [kN] Free end slip [mm] Figure 16 : Numerical simulation of the experimental pullout curves (non-alloy rebar). Figure 17 : Numerical simulation of the experimental pullout curves (galvanized rebar). Numerical results for galvanized + epoxy rebar, presented in Fig. 18, are similar to the ones obtained with galvanized rebars. But it is possible to see that experimental results also present an initial peak of pullout force followed by a softening, after the increase of the pullout force. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 10 20 30 40 50 60 70 80 Envelope(Galvanized + epoxy) Numerical Model (Abaqus) Analytical Model (Sena et al., 2009) Pullout Force [kN] Slip [mm] Figure 18 : Numerical simulation of the experimental pullout curves (galvanized+epoxy rebar). Model with the rebar's ribbing In this section the pullout tests [31] were modelled using the geometrical representation of the rebars’ ribbs. Note that an approximate geometry was adopted due to the complexity of the real rebar ribs geometry. Fig. 4 depicts schematically the adopted mesh, which included 8 ribbs along the embedded length of the steel rebar in the concrete. Three different heights of ribbing were considered in the three distinct simulations that were carried out, respectively, 0.20, 0.26 and 0.30 mm. The ribs allowed to simulate the mechanical reinforcement mechanism due to the rib interlock verified between concrete and ribbing in experimental test. Moreover, the cohesive elements were used to simulate the effects of steel- concrete chemical adhesion and frictional shear. In these simulations the parameters that defined the behaviour of the cohesive elements layer, in terms of nominal stress, are presented in Tab. 8. Fig. 19 depicts the pullout force vs. free-end slip relationships for the performed numerical simulations. The results that better agreed with the experimental results were obtained with a ribbing height of 0.26 mm, where the maximum pullout force obtained in the numerical simulation was similar to the experimental. The stiffness of the numerical response was higher than the one of the experimental results. The horizontal plateau of the pullout force vs . slip curve was not possible to reproduce numerically. Instead, the softening verified numerically was very pronounced.