# Macro-Modelling Approach for the In-Plane Cyclic Response of Cold-Formed Steel Partition Walls
## 2 Damage Mechanism of CFS Partition Walls
### Typical Damage Mechanism of CFS Partition Walls under Lateral Loads  
According to physically observed damages from past earthquakes and failure modes measured from previous experiments [18; 19; 20; 21; 22], possible damage of CFS partition walls under lateral loads can be generally categorized. Damage to CFS partition walls typically initiated with screw pop-out at the GBs attached to the top and bottom tracks. In addition, minor damage also occurs in the form of screw pop-out at the wall boundary, and it is then propagated throughout the wall. Minor crushing of GBs occurs at the wall boundary and is followed in the form of major cracks along the GB joints as incipient joint separation of wall intersections occurs. Furthermore, continued joint separation of wall interactions induces GB loosening due to a considerable amount of screw pullthrough at GB boundaries. More excessive damage involves stud deformation and detachment of GBs. Additionally, the transverse wall is damaged as the stiffer in-plane wall is pushed through at higher drift. The damage mechanism at higher drift levels consists of PAF tearing through the tracks or local buckling of the studs. The buckled region forms a plastic hinge at the studs. Regarding this, several studies revealed that the connections of the tracks to the concrete using PAFs and the connections of the tracks to the study using screws suffer little to no damage [21; 23; 24; 25; 22].  
In this study, the damage mechanism of a typical CFS partition wall configured as a floor-to-floor frame system is simply characterized as shown in Figure 2. Predominant damages of CFS partition walls are assumed to be mainly resulted from the racking behavior of GBs subjected to lateral loads. Note that no critical damage occurred at tracks and/or track-to-RC slab connections and the damage on tracks usually occurs when out-of-plane deformation is imposed onto the CFS partition wall, which is out-of-scope of this paper and will not be, therefore, dealt with. CFS framing members possess negligible lateral resistance since their screw connections have minimum rotational stiffness, hence the hinged CFS frame deforms in the shape of a parallelogram. On the other hand, GBs have substantial in-plane rigidity and rotate as a rigid body remaining nearly rectangular in shape [26]. This incompatible deformed shape between the CFS framing and GBs initially induces a displacement demand at the metal screws. The screw's displacement should be accommodated by a combination of screw tilting and local damage to the GBs. As floor-to-floor relative displacements is increased, similar damage is further developed at higher numbers of screws and GB-to-stud connections. Several screws at the GB-to-CFS framing connections exhibit a variety of damage modes such as tearing and pulling-through. Once the edge of a GB is contacts the RC slab due to the further racking behavior, its corner crushing  
Figure 1: Elements and their dimensions of a cold-formed steel (CFS) partition wall erected by typical Korean construction practices.  
is initiated after the gap closing between studs and tracks, and additional axial compression is then imposed to the stud. The damage of studs such as weak axis buckling might be detected when excessive axial force is applied.