## 4 Numerical Simulation of the RC Frame--Infill Concrete Panel Interaction
By comparing the nonlinear behaviour of the specimens with steel ties to that of the control specimen (without the steel ties), the non-linear shear force versus the relative sliding displacement at the interface due to the presence of the steel ties could be determined. This was used in the current numerical methodology to define the nonlinear  
Figure 21: (**a**) Experimental setup to study the force transfer mechanism between portions of the RC panel and the jacketed RC column with or without steel ties. (**b**) Cross-section [60; 61; 62]. Figure 26: Horizontal displacement versus horizontal load cyclic response of specimen RC-IP 3. Comparison between observed and numerically predicted behaviour. Figure 24: Horizontal displacement versus horizontal load cyclic response of specimen UC-IP 2. Comparison between observed and numerically predicted behaviour. _Numerical Simulation of UC-IP 1:_ The previously described numerical methodology was first applied for specimen UC-IP 1. The numerical response in terms of envelope curve of the horizontal load versus the horizontal displacement at the top beam is depicted in Figure 22, being compared with the corresponding measured experimental cyclic response. The predicted peak load horizontal value is equal to 135 kN and compares reasonably well with the peak measured value equal to 127 kN. The predicted shear strain versus horizontal load response distribution compares reasonably well with the corresponding measured response. The numerically predicted compressive limit state at the corners of the infill panel (Figure 23a) also compares well with the crushing of the corners, which was observed for this specimen during testing (Figure 23b). _Numerical Simulation of UC-IP 2:_ The numerical response for specimen UC-IP 2, in terms of envelope curve of the horizontal load versus the horizontal displacement at the top beam, is depicted in Figure 24. This numerical response is compared with the corresponding experimentally measured cyclic response. The predicted peak horizontal load value is equal to 350 kN and compares reasonably well with the corresponding measured value equal to 338 kN. The predicted shear strain versus horizontal load response distribution compares reasonably well with the corresponding measured response. The observed sudden drop of the bearing capacity for specimen UC-IP 2 is not predicted by this numerical simulation. Figure 25a shows the diagonal tensile limit state numerically predicted at a wide region of this unreinforced infilled panel. This numerical limit state compares reasonably well with the quite wide diagonal cracks spread at most parts of the unreinforced concrete panel, which was observed for this specimen during testing (Figure 25b). _Numerical Simulation of RC-IP 3:_ The numerical response in terms of envelope curve of the horizontal load against the horizontal displacement of the top beam is depicted in Figure 26. In the same figure, the measured cyclic response is also plotted. The numerically predicted peak horizontal load value is equal to 450 kN and compares reasonably well with the peak measured value of 408 kN. The predicted shear strain versus horizontal load response distribution compares reasonably well with the corresponding measured response. The observed sudden drop of bearing capacity for specimen RC-IP 3 is not predicted by this numerical simulation, due to the adopted constitutive law for the RC panel. In Figure 27a, the numerically predicted diagonal tensile limit state is shown; this numerical limit state compares reasonably well with the diagonal cracks observed for this specimen during testing (Figure 27b). The preceding comparison demonstrated that the outline simulation could predict quite well the in-plane bearing capacity of the RC frames infilled with concrete (UC or RC) panels and the corresponding limit states. The numerical simulation of the limit state of the RC panel needs further improvement.