## 1 Introduction  
Cold-formed steel constructions (CFS) are structures designed with small thickness cold-formed steel shapes, manufactured at ambient temperature. During the cold-rolling forming process, sheets are fed longitudinally through a series of rolls until they reach the desired shapes. Cold formed steel constructions (CFS) started to be a great success in the USA and Scandinavia in the mid-20 th century. This structural typology possesses a lot of advantages in comparison with traditional materials such as concrete, where they distinguished the high strength/weight relationship, the speed of construction and the environmentally friendly material, for example. The structural properties or shear walls constructed with cold-formed profiles were determined with tests carried out by [PERSON] of the Santa Clara University [1, 2]. The sheathing stabilizing properties in sections of cold-formed steel profiles had already been analyzed by [PERSON] [3] of Cornell University. [PERSON] [4] continued his work. The design of the American US AISI Specifications [5] is based on the results of such investigations. Nevertheless, the model to include the sheathing stabilizing properties, by means of the shear wall stiffness, could not be verified with the latest tests [6]. In Europe, Eurocode 3 [7] specifies the design provisions for CFS members. Due to the need for understanding the behavior of these structures, especially under the effect of seismic loads, lateral resistance of CFS shear wall panels has recently been studied both experimentally [8, 9] and analytically [9, 10]. [PERSON] and [PERSON] [11] also performed monotonic tests on CFS wall panels and investigated the effect of sheathing material, sheathing thickness, and wall aspect ratio. [PERSON] et al. [12] studied the typical screw connections used to attach sheathing boards on CFS framing members. The use of X-bracing flat strap on CFS wall panels has also been the subject of several studies [8; 13; 14; 15]. [PERSON] et al. and [PERSON] et al. [8; 13] performed monotonic load tests on CFS wall panels utilizing flat-strap X-bracing. [PERSON] et al. [14] performed shake table tests on a CFS structure with flat-strap X-bracing, and reported that the structure exhibited a ductile behavior. Tests done by [PERSON] and [PERSON] [15] on CFS walls with flat-strap X-bracing revealed that the behavior of wall panels was mostly determined by hold-down details. Use of steel sheet as sheathing on CFS wall panels was investigated by [PERSON] [16], and the failure of wall panels was determined to be primarily due to the buckling of steel sheet sheathing and pull out of screws. In a typical CFS construction, in addition to being responsible for resisting lateral loads, CFS wall panels also form the gravity load resisting system of the structure. For this reason, the axial compression behavior of CFS studs and wall panels has also been investigated by several researchers [17; 18; 19; 20]. These studies indicated that the existence of sheathing improved the axial compression behavior of CFS studs with the level of increase in load capacity being affected by sheathing material and screw spacing. The main objective of the study conducted by [PERSON] and [PERSON] [21] was to evaluate the performance of CFS wall panels using oriented strand board (OSB) as sheathing material and subjecting them to monotonic lateral loading. Other similar design methods are unsuccessful in Germany. The intention is to develop a universal design method for shear walls subjected horizontal loads, based on completed research projects [22]. Among these investigations, the tests carried out by [PERSON] and [PERSON] [10], studied the behavior of the CFS wall panels, under the combination of vertical and horizontal loads, testing the model with different types of materials for the sheathing (agglomerate boards with polyurethane, fiber-plaster, wood-cement and trapezoidal sheets).