## 3 Shake-Table Tests of Model with Innovative Infill Connection (Model IW-SB)
### Visual Observations of Damage to the Infill  
Presented further are the photos of damage to the infill during the shake-table tests in respect to the referent Model 1 (Figure 23). The observed damage sequence during testing, including the timing and location of initial cracking, and development of localized shear cracks under defined level of excitation is presented further. Under an input acceleration of less than 0.4 g, the structure experienced negligible-to-slight damage to the first story walls (based on definitions in (ATC, 1998, [41]). At the level of 0.4 g, in both test series, cracks began to form around the perimeter of the infill walls with some crushing at the corners. At 0.8 g, in Model 1, the first and the second story infill walls began to develop inclined cracks at isolated locations. These cracks were formed in both directions. At the end of testing of Model 1 (PGA = 1.2 g), the infill wall adjacent to the door opening collapsed and significant diagonal cracks occurred in the infill panels (Figure 23, left). In contrast, the infill damage at the end of testing of Model IW-SB was concentrated only at the connections of the panel with the RC frame. The infill panels in Model IW-SB were engaged more effectively in resisting the lateral demands and kept their integrity until the last level of excitation of 1.6 g. This observation contributed to the statement that, with the proposed connection, the seismic capacity and in-plane and out-of-plane stability of the infill were significantly improved (Figure 23, right). This failure mechanism demonstrated that full length steel bars strengthened the infill panel and improved its integrity. The infill panel was kept stable because of the six layers of full-length connection bars anchored to the columns. The full-length connection bars did improve the in-plane stability of the infill panel under earthquake excitation; however, the deployed steel bars could also change the crack propagation in the infill panel. Under PGA = 1.6 g, flexural cracks developed in the plastic hinge regions of the columns, and the maximum first story drift ratio reached 2.89%. It should be pointed out that a reliable connection detailing method could provide a stable out-of-plane capacity of the infill panels. The infilled frame exhibited a favorable seismic performance with no observed damage to the RC frame members. It should also be noted that during the entire test series, including the highest excitation levels, no visible slippage of the steel bars was observed. The bars remained embedded and fully engaged with the surrounding masonry. This observation is supported by the damage photographs (e.g., Figure 23), where no signs of movement or disengagement at the interface zones are visible. For Model 1 (as a referent model for comparison) sine sweep tests are performed at the beginning and after the test with earthquake excitation of 0.60 g. The values of the frequency of the model were 8.785 Hz and 3.047 Hz respectively, or the frequency is decreased for 2.90 times. For this model, sine sweep test are not performed after the last series of seismic test of 1.20 g earthquake excitation. However, since Model 1 had already shown visible damage at that lower intensity and IW-SB remained undamaged until 1.0 g, the observed difference in frequencies shown in Table 3 cannot be interpreted as greater stiffness degradation in IW-SB. Rather, it reflects that the IW-SB model endured higher seismic demand before reaching comparable damage levels. It can be seen that the frequency of the Model IW-SB, at the start of the testing, is around 5.6% bigger than for Model 1 (Figure 24, Table 3), which is expected, as both models have the same geometry and mass, and the only difference lies in the frame-infill connection. The IW-SB reinforcement does not contribute additional stiffness in the undamaged state.