# The Influence of Interlock Loss between Rebar and Concrete on Bond Performance of RC Member
## 4 FE Analysis for Reproduction on Beam Loading Experiment
### Validation of Each Element Model  
In order to check the validity of the parameters in the FE model, such as the reproduction of rebar shape by hexahedron elements, the parameters applied for the joint element between steel and concrete, and the parameters of aggregate and mortar elements, a pull-out test of rebar embedded in concrete was reproduced by FE analysis.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Mortar Element** & **Aggregate Element** \\ \hline Compressive strength (N/mm\({}^{2}\)) & 39.7 & 140 \\ \hline Tensile strength (N/mm\({}^{2}\)) & 2.67 & 10 \\ \hline Elastic modulus (kN/mm\({}^{2}\)) & 18.8 & 51.8 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Material property values in analysis model.  
The pull-out test was based on JSCE-G 503-2013 (test for bond strength between concrete and steel reinforcement by pull-out test). Figure 9 shows the outline of the pull-out test. The specimens for the pull-out test were the concrete cubes of 132 mm of each side with a rebar embedded in the center. The length of one side was six times the diameter of the rebar. An unbonded zone of twice the rebar diameter in length was provided on the pull-out side. The relative displacement between the rebar and the concrete cube was measured as the pull-out displacement at a bottom of the specimens. The pull-out test was conducted on a total of four specimens, consisting of two specimens with reinforcement of the screw bar, and two specimens with round PC rod. The properties of steel bars were same as the beam loading test.  
Figure 10 shows the reproduction analysis model. As with the beam model, it consisted of a mortar element, aggregate element, and steel element. Two-dimensional joint elements were placed at the boundaries around the steel element.  
Figure 11 shows the comparison of the test results and analytical results in the load-pull-out displacement relationship. In both the threaded bar and round PC rod cases, the analysis was able to reproduce the behavior until the applied load reached the bond strength. In this pull-out test, displacement measurement around and after failure did not have high reliability. This was because the specimens bounced or split at failure, thus affecting measurement of displacement gauge fixed on the concrete cube surfaces.  
Figure 10: FE analysis model (half slice view).  
Figure 9: Outline of pull-out test.  
Thus, there was slight difference in softening behavior between experiment and analysis, especially after rebar slipping due to bond fracture for round bar. However, it was enough to evaluate the structural behavior of the RC member with interlock and bond performance until bond fracture, which is the focus of this study. Dynamic analysis considering local contingency of slipping can improve slip behavior reproduction between smooth surface due to bond fracture [29].  
From these results, the authors concluded that those models, such as the material properties of the aggregate and mortar elements, and the stiffness, chemical adhesion strength, friction coefficient of the joint element, were valid enough to reproduce the beam tests.