# Global Buckling Investigation of the Flanged Cruciform H-shapes Columns (FCHCs)
## 1 Introduction  
In many multistory steel moment-resisting frames (SMRFs), the regular column is a universal column (UC) or universal beam (UB), as shown in Figure 1a. In many cases, columns are subjected to both axial and bending effects. Therefore, the designer would control mechanical behavior due to the minor axis problem [1]. According to Chinese GB/T 11263-2017 [2], the ratio of the radius of gyration of UC or UB is from 1.69 to 6.55. The minor axis of a UC or UB usually has a capacity significantly less than its strong axis. Therefore, it leads to an axially loaded column in compression buckles about the minor moment of inertia section. The method of connecting multiple single components to improve the carrying capacity of the single-member is already a common practice in cold-formed steel structures and aluminum alloy structures [3, 4]. A similar approach is also used on hot-rolled steel components. For example, UC or UB are combined with Tee-shapes to form the flanged cruciform columns (FCCs), as shown in Figure 1b, which are suitable for the biaxial bending columns [5]. FCCs have some other names, the cruciform column with universal beam section (CCUB) [6, 7], the cruciform column (CC) [8], flanged cruciform sections (FCSs) [9], the stiffened cruciform sections [10], and specially shaped columns with cruciform section [11]. In addition to FCCs, other forms of combinations have also been studied and reported. BWS (Boxed W-shaped section) [12], shown in Figure 1c; SS (side to side) [8], shown in Figure 1d; BBC (built-up battened column) [13], shown in Figure 1e. However, compared to the FCCs, BWS, SS, and BBC often requires internal continuity plates, which is commonto weld at least one side of each plate using electroslag welding (ESW). Still, it is vulnerable to brittle fracture resulting from the notch-like condition created by ESW. The test shows that the bearing capacity of the FCC column with the same cross-sectional area is slightly higher than that of the SS column. [8]. Therefore, FCCs are the better built-up columns. The global stability of steel components is an old and young research topic. For instance, some scholars paid attention to the buckling behavior of steel beams and composite beams with special shapes [14; 15]. Under normal circumstances, there are generally floor restraints in steel frames to limit the global buckling of the beam. Therefore, the global buckling of the frame column is more important than the beam. Many steel design standards provide comprehensive design aids for analyzing and designing standard steel columns. However, few such design aids are available for built-up sections [16], and many design codes [17; 18] do not provide specific design provisions for FCC compression members. Fortunately, some studies focused on or were involved in FCCs [6; 7; 8; 9; 10; 11; 19]. For example, [PERSON]. [6] and [PERSON] [8] proved that the cruciform column using universal beam sections was an efficient built-up section with a larger ultimate axial load capacity, more significant stiffness, and saved the weight of steel used. [PERSON] et al. [10] investigated the stability of steel columns with the cruciform section under constant compressive and shear stresses. [PERSON] et al. [11] conducted the experimental investigation and numerical analysis on the mechanical behavior of FCCs under cyclic loading. [PERSON] et al. [19] studied the instability bearing capacity of the flanged columns with a cruciform section considering residual stress when subjected to axial compression. At present, China has more than 30 hot-rolled H-shapes production lines, with an annual output of 16 million tons. Still, the application of hot-rolled H-shapes in steel structures is only 15-20%. Therefore, increasing the hot-rolled H-shapes application proportion has been included in the government's work schedule. Based on the combined concept of FCCs, the author directly uses three UC or UB, or three UC and UB to form the flanged cruciform H-shapes columns (FCHCs), as shown in Figure 1f.