## 3 Overview of the Proposed Connection Methods and Specimen Design  
As detailed in Chapter 2, the specifications of connections between units, including connector plates, can vary depending on the scope of the module interior and exterior, as well as the construction error. In conventional modular buildings, modular units are generally connected using bolts in conjunction with connector plates, interlocking devices, and steel plate welding. However, current connection systems are not technically or practically suitable for all modular buildings, such as high-rise modular buildings. Here, we describe a novel technology for connecting modular units that can ensure the safety of modular buildings. In this study, straight and cross-shaped metal connectors using rectangular tubular columns and channel beams to connect modules are proposed. If the connectors developed in this study are used, it is possible to connect between modules from inside, rather than from outside the modular building. This is advantageous in terms of construction safety. In addition, the lateral load-resisting capacity of corner section of the modular building will be enhanced if the connectors are installed by applying L- and T-shaped connection systems. Their structural performance is evaluated through cyclic loading tests, in which the story drift angle is controlled in the width and longitudinal directions. Figure 1 shows the connection method for the modular building system proposed in this study. As shown in Figure 1a, one modular frame unit consists of a \(3\times 6\times 3\) m module with \(125\times 125\times 9\) mm (SPSR400) square tubes as column members and \(200\times 75\times 6\) mm (SS400) channels as beams. To connect the \(3\times 6\times 3\) m modules in the up-down and left-right directions, this study proposes a novel system for connecting modular units using straight and cross-shaped connector plates, as shown in Figure 1b. As square tubes were used for the columns, the modular unit connections exhibited similar moment-rotation relationships between the width and longitudinal directions, but these relationships can change depending on the connector plate placement direction. Structural performance was  
Figure 1: Connection details of the modular building system: (**a**) structural plan; (**b**) shape of connector plate. evaluated using cyclic loading tests, in which the story drift angle was controlled in the width and longitudinal directions. The width-to-thickness ratio of the \(125\times 125\times 9\) mm square tubes was 12.8, which is less than the width-to-thickness ratio limit of \(18.9\) (\(=\mathbf{0.64\sqrt{\left\lvert F/F_{y}\right\rvert}}\)) for the compression elements of the compact seismic cross-section specified in KBC 2016 [14]; thus, resistance of the tubes against local buckling was confirmed. The \(200\times 75\times 6\) mm channel beams were manufactured by bending steel plates in accordance with KS D 3530, \"Light Gauge Steels for General Structure\" [15]. The width-to-thickness ratio of the web, being 31.33, was smaller than the seismic compact cross-section slenderness ratio limit of \(72.34\) (\(=\mathbf{2.45\sqrt{\left\lvert F/F_{y}\right\rvert}}\)), but the flange width-to-thickness ratio of 12.5 was greater than the seismic compact cross-section limit slenderness ratio of \(8.86\) (\(=\mathbf{0.30\sqrt{\left\lvert F/F_{y}\right\rvert}}\)) and the compact cross-section slenderness ratio limit of 11.22 (\(=0.38\sqrt{\left\lvert F/F_{y}\right\rvert}\)), and thus this was categorized as a non-compact cross-section. Therefore, it was necessary to reinforce the stiffener at set intervals to prevent local buckling of the channel beams. In the actual module, the resistance against local buckling should be sufficient, as portions of the channel beam upper flange and web are embedded in the concrete slab. When connecting modules together using F10T M16 bolts, the straight connector plate is inserted into the 10 mm gap space between the modules in the upper and lower stories.