## 5 Experimental Results: Comparison and Analysis
### Comparison of Bending Moments  
As the connection involves welding the column and beam, the bending moment applied in this area must be assessed first. As shown in Figure 6a, the members of the cross-shaped test specimens were assumed to be line elements and the reaction force (\(R_{A}\)) in Equation (1) was first calculated on the basis of the force equilibrium; the bending moment (\(M_{b1}\)) applied to the connection was calculated using Equation (2), and the distance between the roller end point of the beam and the connection area (\(L_{b}\)). The same calculation method can be used for the cantilever test specimen, as depicted in Figure 6b. \[R_{a}=P\!\cdot\!H/L \tag{1}\]  
\[M_{b1}=R_{a}\!\cdot\!L_{b}=P\!\cdot\!H/L\!L_{b} \tag{2}\]  
The values thus obtained are the bending moments applied simultaneously to the upper and lower beams; these values may exceed the cumulative values of the plastic bending moment (\(M_{p}\)) for the beam cross-section due to the upper and lower beam composite effect. However, the test specimens used in this study were not connected in any way other than via the connector plates between the upper and lower beams, and thus it was reasonable to carry out the comparison assuming a value four times higher than the beam plastic bending moment. With an average yield strength of 263 N/mm\({}^{2}\), obtained through the \(200\times 75\times 6\) mm channel beam material tests, the bending moment was calculated as 36.1 kN.m. Figure 6: Reaction forces and bending moment diagram: (**a**) cross-shaped test specimen; (**b**) cantilever test specimen. Figure 7 shows the relationship between the bending moment and story drift angle; the bending moment was obtained through substitution on the basis of the aforementioned method. The value four times higher than the beam plastic bending moment is also shown for analysis of connection performance based on the performance standard required for special moment frames. The K-LS specimen was compared to the K-LC specimen, taking into consideration the fact that cyclic loading was conducted only until 0.03 rad. These two test specimens were manufactured symmetrically, with no reinforcement to prevent torsion of the space between the left and right beams, resulting in an increase in the torsion effect; it was estimated that a plastic bending moment of 80% could not be maintained at a drift angle of 0.04 rad during the compressive loading interval (third quadrant). On the other hand, the K-SS and K-SC specimens had relatively small spaces between beams that prevented torsion, maintaining a plastic bending moment of 80% at a drift angle of 0.04 rad during the compressive and tensile loading intervals (first quadrant). The K-LS and K-LC specimens differed in terms of whether a shim plate was installed between the upper and lower beams, as well as in the shape of their connector plates. The cross-shaped connector plate installed in the K-LC specimen was subject to compressive and tensile cyclic loading in the long edge direction of the horizontal plate, and thus the contribution of the vertical plate placed on the bending center line to the overall bending resistance was small. Thus, differences in behaviors until 0.03 rad can be considered to result from the presence of the shim plate. It was observed that installation of the shim plate increased the energy absorption capability or the hysteresis curve area. Differences in behavior according to the shape of the connector plate in the K-SS and K-SC specimens were investigated. A significant difference in the maximum internal force between the first and second loading cycles of 0.04 rad for K-SS, which used a straight connector plate, was seen--stiffness degradation was observed after the maximum internal force was determined near 0.03 rad. By contrast,  
Figure 7: Moment–drift angle relationship of specimens: (**a**) K-LS; (**b**) K-LC; (**c**) K-SS; (**d**) K-SC.