## 4 Results
### Load-Displacement Curve and Stress-Rotation Curve  
Figures 8-10 show load-displacement curves of the connection specimens according to the load direction. As shown in the figures, the upward-direction specimens had the greatest load-displacement capacity, followed by the downward-direction specimens. The lateral-direction specimens were found to resist a low level of moment. For the downward rotation specimens (Figure 8), initial sliding occurred in some specimens due to the slip in the contact section between the pin and the vertical steel pipe. However, there is no problem in calculating the moment-rotation curve since the position of the rotational axis, which is the intersection point of the horizontal pipe's central axis and the vertical pipe's central axis, remained almost unchanged. The yield of the specimen occurred at the pocket in contact with the pin. Since the yield strength of the pocket was the smallest compared with other parts, the yield strength of the pin seems to have dominated the yield strength of the specimen. The yield of specimens occurred at a load range of 1.22 kN-1.91 kN (Average = 1.39 kN, S.D. = 0.06 kN), where the top part of the pocket started to yield. As the load increased, the top part of the pocket was bent and reached its ultimate state, as shown in Figure 5. The maximum loads were in the range of 1.64 kN-2.00 kN (Average = 1.87 kN, S.D. = 0.08 kN). The results of the upward rotation specimens are shown in Figure 9. Unlike the results of downward rotation specimens, the structural behavior of the upward rotation specimen was dominated by the contact section between the vertical steel pipe and the end of the horizontal pipe, as explained in the deformation shape. When the vertical steel pipe yielded, the connection specimen began to yield. The yield load range was 2.95 kN-3.53 kN (Average = 3.28 kN, S.D. = 0.12 kN). As the load increased, the vertical steel pipe gradually bent inward. When the vertical steel pipe reached its ultimate state, the maximum load occurred. The maximum load range was 3.61 kN-4.50 kN (Average = 3.95 kN, S.D. = 0.25 kN). The width of the initial straight line before yielding was relatively smaller than that of  
Figure 8: Load–displacement curves of downward rotation: (**a**) LVDT-1; (**b**) LVDT-2; (**c**) LVDT-3; (**d**) LVDT-4. the downward specimens due to the contact resistance resulting from the surface of the vertical steel pipe. The horizontal displacements of the top and bottom of the vertical steel pipe around the connection point initially indicated different directions, while those of the downward rotation specimens showed the same direction. It means that the pocket-type connection resists upward rotation more strongly. The specimens with the upward rotation have the largest load-displacement capacity. Figure 10: Load–displacement curves of lateral rotation: (**a**) LVDT-1; (**b**) LVDT-2; (**c**) LVDT-3. Figure 9: Load–displacement curves of upward rotation: (**a**) LVDT-1; (**b**) LVDT-2; (**c**) LVDT-3; (**d**) LVDT-4. For the specimens with lateral rotation, the smallest load-displacement capacity is shown in Figure 10. The range of initial stiffness was very wide, and the yield of specimens occurred at a load range of 0.13 kN-0.58 kN (Average = 0.46 kN, S.D. = 0.09 kN). As the load increased, the connection pocket of the lateral rotation specimens deformed in the direction of the rotation, and cracks occurred in welded part. Thus, the specimen began to yield in the low load, and the resistance capacity was dominated by the rotational stiffness of the pocket and the welded part. The maximum loads were in the range of 0.59 kN-0.72 kN (Average = 0.66 kN, S.D. = 0.04 kN). The difference between yield load and maximum load is relatively small. The stress-strain curves are investigated to analyze the behavior caused by the rotation of the pocket-type connections.