# 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  
#### 2.1.1 Damage Type 1: Damage Associated with Stirrups and Hoops (RC Detailing)  
The philosophy behind the confinement effect is more straightforward and better understandable by all the scientific and professional community. When the concrete is subjected to high compressive loadings, a fragile crushing occurs along the principal compression loading direction. The confinement provided by the stirrups prevents, or at  
Figure 3: Interaction between the most common damages observed in RC structures due to earthquakes. Figure 2: Types of damage in infilled RC frames when subjected to earthquakes. least delays, the concrete detachment. The concrete strength and especially the ductility also improves considerably. The confinement effect depends on the stirrup diameter, the stirrups spacing, the longitudinal reinforcement, the steel quality and the shape of the stirrups [13]. According to the Eurocode 8 recommendations regarding the stirrups folding (\(135^{\circ}\)), the execution of the stirrups folding is frequently overlooked, resulting in their poor efficiency and, particularly, in the stirrups failure during the seismic event. It is possible to find some examples of RC building structures that, during an earthquake, suffered damage in their RC columns due to inadequate transverse reinforcement, namely poor detailing and designing. Figure 4 shows examples of damage observed following the Gorkha, Emilia-Romagna and L'Aquila earthquakes [9; 14; 15]. It is recommended adequate confinement of the concrete core of the columns and beams in the plastic hinge regions to prevent strength degradation or fragile failure due to shear and flexural demands and increased ductility. This need for confinement is even higher when the column is subjected to high axial and shear loadings. During an earthquake, the failure of beams and beam-column joints is usually related to the inadequate use of transverse reinforcement and confinement. These failures are commonly observed at a local level and may not result in the total collapse of the building structure. A ductile behaviour can be achieved if a proper and adequate seismic design is carried out, with appropriate transverse reinforcement and detailing. Without a refined design and detailing of the transverse reinforcement, a fragile behaviour can occur during an earthquake, and the probability of occurring columns' failure is higher. Figure 4: Damage type 1—example of post-earthquake damage in RC columns: (**a**) absence of transverse reinforcement, (**b**) hoops’ poor detailing, (**c**) large spacing between stirrups and (**d**) insufficient transverse reinforcement. 1.2 Damage Type 2: Damage Associated with Longitudinal Reinforcement Detailing (Bond, Anchorage and Lap Splices)  
The correct and adequate design of the connection allows the concrete and steel reinforcement to form a composite structure. The effectiveness of this connection is fundamental under cyclic loads and when smooth bars are adopted in old existent structures. However, in the case of new constructions designed according to Eurocode 2 [16] and Eurocode 8 [8], the use of smooth bars is not specified. Some of the basic rules/procedures during the detailing/designing stage to ensure better performance of the reinforcement bond and anchorage are listed below:  
* Splices and anchorage in regions where it is expectable that the occurrence of cracking of the surrounding concrete (plastic hinge length) should be avoided;
* Concrete with anchorages and embedded splices should be well confined to prevent the concrete expulsion;
* Compression in the transverse direction to the reinforcement bond positively affects and prevents the concrete expulsion. Some examples of this type of damage are shown in Figure 5. They are reported due to poor and inadequate detailing of the longitudinal and transverse reinforcement and to the use of smooth bars.