# The Influence of Interlock Loss between Rebar and Concrete on Bond Performance of RC Member
## 4 FE Analysis for Reproduction on Beam Loading Experiment
### Results of Reproduction Analysis of Beam Loading Test and Discussion  
Figure 12 shows comparison between the analytical and experimental load-deflection relationship and the primary principal strain distribution. For the ST-100, the analysis was able to reproduce initial stiffness, load capacity, strain distribution of main rebar, and crack distribution observed in the experiment. For the ST-50, analytical stiffness value was lower than the experimental value at approximately 250 kN, and shear failure occurred at higher load than that in the experiment. As the analytical model uses a smeared reinforcement model for the shear reinforcement, the confinement effect by stirrups for main rebar cannot be considered directly. In this analysis, among the joint elements in the ST-50 model, a large value was applied for the chemical adhesive strength at the locations of the stirrup in the experiment to reproduce the confinement effect by the stirrup. However, as the load increased, the stress in the direction for the detachment was concentrated around the joint elements which have high adhesive strength, and at a load of approximately 250 kN the rebar detachment occurred. The shear capacity of beam increased, and as a result, the maximum load is considered to have been higher than that recorded in the experiment. ST-50 in analysis failed in shear, but the angle of the shear cracks was steep, and the crack shape was similar to those of PL-50 in the experiment. If interlock between the top concrete and the lugs on the rebar can be maintained by the discrete representation of the stirrups mechanically, the detachment can be prevented, and the accuracy can be improved.  
Figure 11: Rebar pull-out test reproduction analysis results (**left**: threaded bar, **right**: round PC bar).  
The analytical result of the ST-0 showed different behavior from the experiment; a decrease in load occurred at a load of approximately 110 kN, and later the load increased again. In the analysis, slip between rebar and concrete occurred at the load of approximately 110 kN, and slip occurred instantaneously in most surface of the rebars. On the other hand, in the experiment, slip between rebar and concrete occurred locally and it was intermittent as the load increased, which may have caused the difference in the load-deflection curves. In the load-deflection curve obtained from the ST-0 experiment, the slope of the curve began to decrease from approximately 120 kN. Slipping sound was intermittently heard from approximately 100 kN during the loading test, presumably indicating that the rebar began to slip. The load at which slip of the rebar started is consistent between experiment and analysis. The strain distribution of the ST-0 clearly showed a decrease in the number of cracks and the concentration of strain in the concrete at the anchoring parts at the beam ends compared with the sound case, reproducing the crack behavior and the failure mode in the experiment. Although there was a difference in stiffness after rebar slip, the maximum load was almost the same as that in the experiment. Rebar slipping is a dynamic phenomenon of intermittent local slipping, and it is difficult to track it in static analysis. The authors believed that the reproduction accuracy of the ST-0 can be improved by introducing dynamic analysis, setting parameters non-uniformly for the joint elements, or by introducing viscous behavior.  
However, as long as a member uses a deformed bar, this beam model can be considered to have enough accuracy. That was because stress transfer by lug can be reproduced well and this model gives safe side evaluation for low bond conditions, e.g., round PC rod.