## 1 Introduction  
By increasing the speed of development in various industries, there is a need for well-engineered warehousing systems to store the products in safe and secure warehouses before they are distributed to the market. For this purpose, cold-formed steel (CFS) storage rack structures have widely been developed to be used in different industries. Uprights are one of the main parts of the racking structures which have the important role of bearing loads like what columns do in buildings. The performance of racking frames depends on the overall behavior of the uprights, as these thin-walled structures are subjected to loss of stability due to the combination of different failure modes, such as the interaction of distortional and flexural buckling [1, 2]. The stability of uprights in racking systems also becomes more critical under extreme loading scenarios [3, 4, 5, 6]. The compressive behavior of upright racking systems has been extensively studied in recent years. Experimental tests on stub uprights and full upright frames were carried out by [PERSON] [7] in order to obtain a set of reduction coefficients for the effective length of the uprights under compression. Local buckling of stub column members under axial load was experimentally investigated by [PERSON] et al. [8] and the results were compared with theoretical relations as well as the numerical method. They concluded that for the design stage of racking uprights, extensive experimental testing is not necessarily required. In another study, [PERSON] and [PERSON] [9] investigated that the predicting ultimate load capacity of upright sections provided by EN 15512 [10] specification is more accurate than predictions by Rack Manufacturers Institute (RMI) specifications. Comprehensive experimental tests on individual components of racking systems were also carried out by [PERSON] & [PERSON] [11], and some clarifications of the guidance provided by EN15512 [10] were presented in order to accurately determine the in-plane global stiffness of the upright frame. The interaction of buckling modes of racking upright members has also been under the attention of researchers in recent years. The local-distortional buckling interaction in fixed-end CFS uprights was experimentally assessed by [PERSON] et al. [12]. In another project, local-distortional buckling interaction of short upright columns was studied by [PERSON] et al. [13] through the concept of reduced thickness of the stiffeners. They reported that the current design codes are not accurate and the effect of buckling interaction needs to be also considered. In another study, [PERSON] et al. [14] experimentally evaluated the distortional buckling of upright frames with different heights and provided design formulations based on the combination of distortional and global buckling modes. In terms of perforation, which is an important parameter that can affect the performance of upright sections under compressive load, [PERSON] et al. [15] investigated the effect of perforation on compressive behavior of storage rack uprights. They showed that the perforation could significantly affect the load-bearing capacity as well as buckling failure mode of the system. The influence of perforation pattern including of perforation position, dimensions, and quantity on the compressive behavior of upright frames were also assessed by [PERSON] and [PERSON] [16]. A series of experimental tests were conducted by [PERSON] and [PERSON] [17] to examine the effect of perforation on the stability behavior of upright frames. In another study [18], they indicated that direct strength method is not enough for the design of rack structures and the experimental test is also required; accordingly, the design approach for upright sections must be based on experimental test procedures. [PERSON] [19] also determined the effect of perforations and applying load on the upright strength through the axial tests on both perforated and non-perforated uprights with various length and load eccentricities.