# A Review of the Performance of Infilled RC Structures in Recent Earthquakes
## 2 Seismic Behaviour of Infilled RC Structures: Definition of Damage Type
### Representative Damage Type Observed in RC Buildings Due to Earthquakes
#### 2.1.10 Damage Type 10: Damage in Non-Structural Elements
The walls collapse can occur since mechanical connections are not used between the 'non-structural' panel and the RC frame. The problem also becomes more severe in these cases due to the usual high slenderness of infills in existing buildings, generally made with two leaves (not adequately connected). As a result, the overturning of the infills is usually observed in post-earthquake field missions, as shown in Figure 22, enhanced by the combination between the damage due to in-plane actions and the transverse acceleration demand during a seismic event. Figure 20: Damage type 10—damage in infill panels: diagonal cracking: (**a**) L’Aquila, Italy, 2009; (**b**) Lorca, Spain, 2011; (**c**) Gorkha, Nepal, 2015 and (**d**) Chiapas, Mexico, 2017. Figure 21: Damage type 10—damage in infill panels: (**a**,**b**) sliding cracking; (**c**,**d**) corner crushing. Figure 22: Damage type 10—damage in infill panels: OOP collapse in low-medium RC structures: (**a**) L’Aquila, Italy, 2009; (**b**) Lorca, Spain, 2011; (**c**) L’Aquila, Italy, 2009 and (**d**) L’Aquila, Italy, 2009. OOP collapses in RC structures composed of 3-5 storeys. As shown in the Figure 22, the level of destruction caused by the panel collapse is high, representing a significant risk for human life safety and economic losses. The OOP collapse was also observed in medium-high RC structures, Figure 23, in the intermediary levels comprised of the panels' total failure and consequent collapse. In addition, some other panels with openings, which suffered damage due to the in-plane seismic demands, partially collapsed. Different investigations were carried out concerning the OOP behaviour of masonry infill walls, from which it was concluded that the OOP strength reduces with the increasing of the panel slenderness [30; 31]. [PERSON] et al. [31] performed a series of OOP tests assessing the effect of the walls slenderness in their OOP behaviour. Before the OOP tests, the walls were subjected to different in-plane damage levels (Low--0.30%; Medium--0.60% and High--1%). Hollow clay horizontal units were used to construct the scaled walls with slenderness equal to 22.9 and 15.2. It was observed during the tests a more significant decrease of the OOP maximum strength and initial stiffness for the thinner panels. [PERSON] et al. [32] carried out a testing campaign to study the effect of the panel aspect ratio (1.28 and 1) in their OOP response. The authors found that square and rectangular infills have very different damage states. For examples, the rectangular walls showed more damage than the square ones. Furthermore, for panels previously subjected to low in-plane drift (0.30%), the square panel exhibited a strength reduction of 24%, while the rectangular panel reduced by about 52%. Figure 23: Damage type 10—damage in infill panels: OOP collapse in medium-high RC structures (**a**) Chiapas, Mexico, 2017; (**b**) Chiapas, Mexico, 2017; (**c**) Chiapas, Mexico, 2017 and (**d**) Chiapas, Mexico, 2017. The in-plane and OOP behaviour interaction seems to be one of the most critical issues. Different authors report that the previous damage reduces the panel OOP strength [31]. The damages caused by prior IP demands affect OOP performance's infill walls, causing the reduction of the maximum strength capacity and modifying the expected failure mechanism. Some experimental works [4; 5; 6; 7; 8; 9] were developed to study this behaviour interaction by performing OOP tests on panels first subjected to different in-plane damage levels. [PERSON] et al. [33] carried out a testing campaign comprising three infill panels made with solid clay bricks (SCB) units (slenderness = 33.9). The reference specimen was subjected only to a uniform monotonic OOP loading and reached a maximum peak load of 8.18 kN/m\({}^{2}\). The remaining models were tested first to in-plane loading demands with different target drift levels, namely 0.22% and 0.34%. After that, the panels were subjected to monotonic OOP loading until the panel collapses.