# Bearing Behavior of Cold-Formed Thick-Walled Steel Plates with a Single Bolt
## 1 Introduction  
Cold-formed steel sections are widely used in civil engineering. In the early stages, only thin-walled steel could be manufactured. With the improved technology of cold forming, more and more cold-formed steel members have been applied in practice, with thicknesses beyond the traditional limitations specified in the codes of thin-walled steel members [1; 2; 3]. In the new version of the AISI standard (2016 edition) [4] and the Chinese GB standard (GB 50018-draft standard for discussion) [5], the thickness of cold-formed steel members was increased to 25.4 mm. However, design criteria based on the study results of hot-rolled steel was adopted in the codes when the thickness of the steel plates in bolted connections was beyond a certain limitation. For example, the standard of AISI S100 [4] specifies that, for bolted connections in which the thickness of the thinnest connected part is greater than 4.76 mm, ANSI/AISC 360 [6] shall apply. Similarly, EN 1993-1-3 [2] specifies that, for a thickness larger than or equal to 3 mm, the rules for bolts in EN 1993-1-8 [7] should be used. Thick-walled steel is usually used in tubular members. The ductility of steel is expected to decrease with an increase in strength during the process of cold work. According to the research of [PERSON] et al. [8] and [PERSON] et al. [9], the ratios of tensile strength and elongation at the fracture between the flat element and the virgin material are in the range of 1.03-1.20 and 0.81-0.90, respectively, and these ratios are in the range of 1.44-1.64 and 0.32-0.44 for corner elements. In the design of bearing-type bolted connections, the strain hardening properties of the plate material are utilized, and the design is based on the ultimate tensile strength of the steel. Additionally, bearing resistance is developed, accompanied with significant plastic deformation around the bolt hole due to high stress concentration [10]. For hot-rolled steel, which has a favorable ductility, a fully developed bearing resistance can be ensured, and the ductility requirement of steel is implicitly included in the design criteria. Therefore, it is necessary to check whether the current calculation formulae, which are derived on the basis of the behavior of hot-rolled steel, are still applicable to the bolted connections of thick-walled steel. Most studies have focused on the bearing behavior of the bolted connections of cold-formed thin-walled steel plates. For example, [PERSON] et al. [11] investigated the effect of curling on the ultimate strength of a thin-walled steel single shear bolted connection. They proposed a revised design formula, accounting for the strength reduction effect of curling and the conditions of curling occurrences. [PERSON] et al. [12] conducted full-field measurements to investigate the influence of the interactions between the holes in the plates of cover-plate steel bolted connections. Numerical models showed the complexity of the stress distribution around the holes. [PERSON] et al. [13] and [PERSON] et al. [14] studied the ultimate tilt-bearing capacity and shear-out capacity of the bolted connections of cold-reduced steel sheets, respectively, and proposed modified formulae. The former found that the tilt-bearing capacity is not significantly affected by the orientation of the bolt head or nut. The results of the latter showed that the edge distance of the bolt connection affects the failure mode, but it has insignificant effects on the shear-out capacity. [PERSON] et al. [15] presented an application of the digital-image-correlation-based technique to investigate the block shear failure mode of bolted connections made of high-strength cold-reduced sheet steel. The experimental results provided a better understanding of how the failure of the bolted connections progressed. [PERSON] et al. [16] studied the ultimate strength and failure sequence of the single shear bolted connections of thin-walled carbon steel. They found that the end distance had the greatest influence on the effective range.