# 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  
Infills represent the external skin of the RC structures; they are generally used as interior partitions and to separate the inner spaces from the outside. Constructive techniques strongly depend on each country's construction practice (double or single leaf infill, connection system between infill panel and the surrounding frame, and workmanship). This aspect can introduce a significant heterogeneity in the influence of infills on the RC buildings performance due to earthquakes. Infill panels generally increase the lateral stiffness and strength, at least at low displacement demand, and profitable growth of the dissipated energy during ground motion. On the contrary, the infill panels can induce significant detrimental effects, positively affecting the damage-limitation performance level and potentially dangerous for life-safety, as discussed in the following remarks. Figure 17: Damage type 9—damage in secondary elements: (**a**) partial collapse of the stairs; (**b**) absence of proper connection between the stairs and the primary structural-resistant system; (**c**) excessive deformation of the cantilever—general view (**d**) use of props to support the cantilevers with excessive deformation. Figure 18: Examples of masonry parapets collapses in the Lorca (Spain) earthquake (adapted from [PERSON] et al. [15]). The infill masonry walls tend to detach from the envelope frame for low seismic demands, as proved by the cracking around the panel contours. Besides using different types of masonry units (solid or hollow bricks), the in-plane detachment of the panels tends to occur due to their incapacity to follow the frame deformation during the seismic event, as shown in Figure 19. Multiple examples are herein presented following the earthquakes in Spain in 2011 (Figure 19a), Nepal in 2015 (Figure 19b), Mexico in 2017 (Figure 19c) and Ecuador ((Figure 19d)). Moreover, it is well-known, infill panels generally exhibit a diagonal damage pattern due to the horizontal action parallel to their plane, as shown in Figure 20. Such damage can be more or less diffused across the building and generally concentrated at the lowest floors, where the relative displacement demand is typically higher. Such damage is clear evidence of the interaction of infills with the RC structure seismic response. Therefore, their typical definition of 'non-structural' components can be considered as not appropriate. Furthermore, the infill panels damage is often particularly severe under moderate seismic shaking, proved by the economic seismic losses reported in recent earthquakes [29], and casualties, thus reducing the seismic resilience of the communities in seismic-prone areas [5]. Figure 19: Damage type 10—damage in infill panels: detachment of the panel from the envelope frame: (**a**) Lorca, Spain 2011; (**b**) Gorkha, Nepal, 2015; (**c**) Chiapas, Mexico, 2017 and (**d**) Muisne, Ecuador, 2018. Some other damage mechanisms commonly found in the infill walls due to the in-plane seismic demands were the sliding cracking and the corner crushing. The sliding failure is typically characterised by a horizontal crack at the panel middle height. It is justified by its high in-plane stiffness, which reduces the capacity to deform and then develops the sliding along the horizontal bed joints. This type of damage was often observed in the Gorkha earthquake in Nepal due to the solid clay bricks commonly used there to build the infill walls. These type of bricks are combined with cementitious mortars resulting in panels with high in-plane stiffness. Some examples of this type of damage are shown in Figure 21a,b. In addition, the accumulation of the stresses transferred by the in-plane loading demand can result in the bricks crushing. This type of damage, shown in Figure 21c,d, is often combined with diagonal cracking or detachment of the panel. One of the biggest problems related to the infill walls was the high number of out-of-plane (OOP) collapses (or overturning) observed.