## 4 Lateral Resistance of Modular Beam-Column Connections
### Hysteresis Curves and Discussion  
Figure 11 presents the hysteresis curve of Specim IC_OB_F and its backbone curve. It also indicates the failure sequence of main structural components of the specimen and the drift ratios at which each failure occurred. The details of the failed structural components are given in Figure 12. At the drift ratio of 2%, the ceiling beam yielded (Figure 12a), and the local buckling at its flange and web were observed at the drift ratios of 4%, respectively (Figure 12b). The welded connection between the ceiling beam and column on the left side was fractured at the drift ratio of 5% (Figure 12c), which was followed by the same type of failure at the welded connection on the right side (Figure 12d). The hysteresis and backbone curves of Specim IC_OB_B are plotted in Figure 13. It also indicates the failure sequence of main structural components of the specimen and the drift ratios at which each failure occurred. The photos of the failed structural components at major loading steps are provided in Figure 14. Both of the ceiling and floor beams yielded at the drift ratio of 1% (Figure 14a), and the local buckling at the flange and web of the ceiling beam was followed at the drift ratio of 3% (Figure 14b). The knee bracings started to yield at the drift ratio of 4.5% and they completely buckled at the drift ratio of 5% (Figure 14c). At the drift ratio of 6%, buckling occurred at the flange of the floor beam, and shear failure happened at one of the blinded bolts connecting the connection plate and lower module (Figure 14d). Figure 15 compares the backbone curves of the two specimens plotted in Figures 11 and 13 with the corresponding panel zone displacement curves, due to shear deformation. The panel zone displacement was computed from the measured displacements by the LVDTs Nos. 4 and 5 by following the procedure discussed in the works of [PERSON] and [PERSON] [23] and [PERSON] and [PERSON] [24]. The results in the figure indicate that the maximum panel zone displacements of Specimens IC_OB_F and IC_OB_B are only 14.1% and 5.7% of the entire lateral displacements obtained from the corresponding backbone curves, respectively. This implies that the modular panel zone proposed in this study remains in the linear elastic range during most of the hysteresis procedure, and thus it has a sufficient level of strength and stiffness so that no premature failure occurs in the panel zone. In addition, it can be seen from the result that the existence of the knee bracings is helpful to reduce the shear deformation of the modular panel zone since the maximum panel zone displacement of Specim IC_OB_F is almost the half of that of Specim IC_OB_B. Figure 12: Failure sequence of Specim IC_OB_F. Figure 14: Failure sequence of Specim IC_OB_B. Figure 13: Hysteresis and backbone curves of specimen IC_OB_B. Figure 16 plots the ratio of the principle strain to the yield strain measured by the three strain gauges No. 21 to 23 during the entire hysteresis cycles. This figure reveals that the maximum values of the ratio are only 14.7% and 19.6% in the case of Specimens IC_OB_F and IC_OB_B, respectively. This indicates that the connection plate between modules did not yield in both specimens, and thus it retains sufficient strength to resist the lateral cyclic loading considered in this study. Several important conclusions can be drawn from the test results. First, the proposed blind-bolted modular beam-column connection has a sufficient level of strength, and did not fail before the failure of other structural components. The shear failure of a single blind bolt was first observed at the drift of 7% only in IC_OB_B specimen. Second, the failure of beam members occurred before that of the column members, which reveals that the strong column-weak beam concept was successfully implemented in the proposed modular system. Third, the knee braces are very effective to increase the stiffness and strength of the proposed modular connection.