# Structural Performance of a Precast Concrete Modular Beam Using Bolted Connecting Plates
## 1 Introduction  
Prefabricated modules improve the speed of construction, efficiency of material usage, and worker safety, but they impose limits on construction, e.g., related to module size. Modular structures consist of modular units that are appropriately sized and are assembled on site. Structural performance and serviceability can be ensured if the modules are connected sufficiently. Therefore, studies have investigated connection methods between modular units to improve the stability and integrity of the modular structure. In the modular construction industry, both steel modules and concrete modules have been adopted with the connection method depending on the type of module. Steel modules weigh half as much as concrete modules and have advantages related to transportation and lifting. Concrete modules have benefits in terms of corrosion and seismic resistance. Welding is generally not used due to the need for skilled welders; instead, bolted connections are typically used on-site to assemble steel modular joints [1]. The connecting plates are attached at both ends of the modules and then are connected using bolts; this method may impose constraints on the arrangement of the modules, since the plates have to be connected to the modules externally [2]. Many studies have been conducted to propose bolted connections that place no constraints on the arrangement of modular units [3; 4; 5; 6]. [PERSON] et al. [2] proposed T-shaped beam-to-beam modular connections, which can ensure convenient installation and eliminate on-site welding. The components of this proposed connection method were a plug-in device and plate with welded stiffeners. The upper module and bottom module were assembled using the plug-in device and a plate connected by bolts. [PERSON] et al. [2] confirmed that stiffeners can effectively increase the stiffness, but gaps would form between the upper and lower columns due to insertion of the plug-in device. These gaps influencethe deformation patterns and bending moment distribution. [PERSON] et al. [3] proposed a beam-to-beam bolted connection using a C-section beam. The connection plate was inserted between the upper and lower modular units, which consisted of a C-section beam fastened with bolts. The shape of the connection plate varies depending on whether it is being used on an inside, outside, or corner joint, so that the appropriate type can be used based on the placement of the modular units. Recently, studies have been conducted to suggest appropriate design methods that can consider a range of different connection types [7; 8; 9]. [PERSON] et al. [7] pointed out that connections for modular units are a relatively new structural form in comparison with traditional steel structures with fixed or flexible beam-to-column connections. [PERSON] et al. [7] proposed the governing equation for determining the effective length factor for connections between modular units. In the modular connection method, developed by previous researchers, steel plates used as the connection method between the modules are installed on the surface of each modular member using bolts. A large number of bolts are required for perfect bonding of the steel plate and the modular members, and a dense arrangement of bolts may cause damage to the modular members. In addition, connection using steel plates suffers from alignment issues and corrosion problems [1]. Unlike steel modules, precast concrete (PC) modules have reinforcing bars (rebars) inside each module, so connection between the rebars must be considered when the modules are connected. The rebars in the PC module are connected through a lap splice, welded splice, or grouted splice sleeve [10; 11; 12; 13; 14; 15]. The grouted splice sleeve is the connection method used most widely. Two rebars are inserted into each sleeve and connected by pouring non-shrink, high-strength grouting material through grout ports. [PERSON] et al. [13] conducted a cyclic loading test to investigate the seismic performance of precast concrete structures connected by grouted splice sleeve.