# Bearing Behavior of Cold-Formed Thick-Walled Steel Plates with a Single Bolt
## 3 Experimental Observations and Test Results  
### Failure Modes  
Similar failure modes were observed for the specimens with 6 mm and 10 mm thick steel plates. Therefore, only the 10 mm thick specimens were presented to show the effect of different end/edge distance combinations on the failure modes. Figure 4 shows the failure modes of the specimens under different end distances, and the edge distance is fixed at 3.0\(d_{0}\).  
The specimens in Figure 4 all failed due to excessive bearing stress in front of the bolt hole, and the failure of these specimens was accompanied by fractures at the edge of the elongated bolt hole in two symmetrical locations that were oriented at approximately 45 \({}^{\circ}\)C and 135 \({}^{\circ}\)C to the axis of loading. The elongation of the bolt hole was composed of two components of deformation, including the protrusion of the bolt from the plate material and the embedment of the bolt into the plate material. The largest bolt protrusion was observed in specimen D10-1.0-3.0. With an increase in the end distance, the proportion of  
Figure 4: Failure modes of 10 mm thick specimens with varying end distances.  
Figure 3: Set-up of the lap shear test.  
the bolt protrusion was reduced, and the proportion of the bolt embedment grew. Both a large shear fracture and significant bearing deformation were observed in specimen D10-2.5-3.0.  
Figure 5 presents the failure modes of the specimens under different edge distances and a constant end distance of \(1.5d_{0}\). For the specimens in Figure 5, the failure modes and deformation of the bolt hole were governed by the value of the edge distance. With an increase in the edge distance from \(1.0d_{0}\) to \(2.0d_{0}\), the failure modes of the specimens were a net-section fracture to shear-out, and the deformed zone was from the longitudinal side of the bolt hole to the front side.  
Two typical failure modes were observed in our tests, including shear-out and a net-section fracture. Shear-out occurs when the end distance is relatively small. The material in front of the bolt yields and is pushed out from the plate, creating two shear planes. The connection fails when the material in the shear planes reaches its ultimate strength. The shear-out failure can be very ductile for hot-rolled specimens, and no fracture occurred [14]. Lower ductility is expected in cold-formed specimens due to less development of the local plastic deformation of cold-formed steel plates. Meanwhile, a fracture was observed along the shear planes of cold-formed connecting plates.  
A net-section fracture occurs when the edge distance is relatively small, as shown in Figures 4(b) and 5(a). The fracture appeared after the necking of the net section during which bolt-hole elongation developed. The structural response of such failure has a relatively low ductility. With a further increase in the edge distance, the net-section strength of the steel plate was approaching shear-out strength, and a mixed deformation was observed along both the longitudinal side and the front side of the bolt hole, as shown in Figure 5(c).