# Experimental and Numerical Studies on the Structural Performance of a Double Composite Wall
## 1 Introduction  
The precast concrete (PC) method has been widely used in the construction of underground parking lots, logistics warehouses, and semiconductor fabrication plants to achieve rapid construction [1, 2, 3]. Especially in the case of semiconductor plant construction, underground work needs to be conducted to secure spaces for large-scale facilities, such as purification systems; thus, a basement wall with a height of 10 m or more is built [4]. If a reinforced concrete (RC) method is applied to the basement wall, the construction period may be significantly delayed because it requires temporary work and concrete curing time to ensure the required strength. For this reason, research has been continuously carried out on the development of a PC composite wall capable of facilitating the quality control of concrete and decreasing the construction period [5, 6, 7]. [PERSON] and [PERSON] [5] and [PERSON] and [PERSON] [6] developed a mega double wall (MDW) in which two PC panels were connected by a concrete link beam and in-filled concrete was poured into the hollow part; they then conducted an experimental verification of its structural performance. [PERSON] et al. [7] developed a precast concrete double wall (PCDW) where internal and external PC panels are connected with a truss-shaped reinforcement, and proposed a design method for the field application of PCDW. In addition, [PERSON] et al. performed a detailed comparative analysis of the constructability and economic efficiency of PCDW and RC walls. [PERSON] and [PERSON] [8], [PERSON] et al. [9], and [PERSON] et al. [10] conducted experimental and analytical studies on double skin composite PC walls that can ensure high strength and stiffness, and [PERSON] et al. [11], [PERSON] et al. [12], [PERSON] and [PERSON] [13], and [PERSON] et al. [14] performed research to investigate the structural performance of concrete wallsstrengthened with steel members. In particular, [PERSON] and [PERSON] [13] proposed a shear strengthening method in which reinforcing bars are inserted after perforating the basement wall. They verified through experiments and finite element analysis that the wall with the reinforcing bars inserted shows a greater than 80% increase in shear strength compared with the existing walls without shear reinforcement. Meanwhile, in South Korea a double composite wall (DCW) system--a new type of basement wall, as shown in Figure 1--was developed [4], and it has been actively applied in construction sites since then. The DCW is completed by pouring cast-in-place (CIP) concrete after assembling two prefabricated PC panels with bolts in a factory. The DCW has an advantage in that it provides excellent constructability because two PC panels are simply connected together by bolts, which also ensures a high level of safety, as the lateral pressure that occurs while pouring CIP concrete is controlled through the bearing stress at the bolted connection. Moreover, because the assembled PC panel plays a role as a formwork, additional temporary works are not required when CIP concrete is cast into the hollow section. The shear key of the PC panel not only facilitates assembly, but also makes an effective contribution to the horizontal shear resistance mechanism after the CIP concrete composite. Figure 2 shows the sequence of the actual construction process for the DCW system. First, PC panels are produced in a PC factory, and two panels are assembled with bolts, as shown in Figure 2d. Subsequently, the assembled PC panel is installed on the foundation, and CIP concrete is then poured into the hollow part to complete the DCW. When a bending moment acts on the DCW, dowel bars embedded in the foundation resist tensile force at the foundation-wall connection, as shown in Figure 1, while reinforcing bars placed on the flange of the PC panel resist tensile force at the center and top of the wall. Figure 1: Characteristics of the double composite wall (DCW) system.