# Experimental Study on an Optimized-Section Precast Slab with Structural Aesthetics
## 1 Introduction  
The precast concrete (PC) construction method can reduce construction costs by shortening the construction period and can improve the member quality by prefabricating the members at the factory [1; 2; 3]. It has thus been widely applied to underground parking lots, parking towers, warehouses, and large sales facilities [4; 5]. Some PC structures, however, have often had problems with cracks or water leakages in the connections of the PC members due to their lack of integrity. For this reason, a half PC system that typically consists of lower PC parts that are prefabricated in a factory and upper parts that are cast in place has been widely used [6]. For PC slab systems, flat, hollow core, and double Tee types are also often utilized with the half PC method. In the half PC method, the external loads in the construction stage should be resisted by the PC members only; otherwise, it requires supporting posts which is costly and therefore reduces a huge advantage of PC construction methods. Many alternatives have thus been developed to enhance the load carrying capacity of PC slab members at the construction stage [7; 8; 9; 10] and PC slabs with vertical ribs, such as a modified double tee slab (DTS) and a multi-ribbed slab (MRS), are some examples [11; 12; 13; 14; 15]. In addition, many efforts have been made to develop slender half PC members with a long span-to-height ratio (\(l/h\)) to maximize space utilization while ensuring efficient structural resistance performance. In this regard, this study developed an optimized-section precast slab with structural aesthetics (OPS) that can reduce the quantity of materials through the efficient configuration of cross-sections, and one that is suitable for long-span implementation as a type of half PC slab. As shown in Figure 1a,b, the OPS has a flange on the top in the center of the span and on the bottom at the end of the span and can thus effectively resist the bending moment, as shown in Figure 1c. In addition, it is designed to ensure shear performance by increasing the cross-section as an in situ concrete topping is placed between the end ribs, and also to highlight the structural aesthetics by making the variable cross-section at the bottom of the member curved in the section optimization process, as shown in Figure 1d. Figure 2 shows the manufacturing process of the OPS at a precast plant. The steel form is installed on the prestress bed and work for the prestressing strands is performed. Then, prefabricated reinforcements are placed in the steel form and concrete is poured and cured by steam, thereby completing the PC unit. Figure 2e shows a PC unit member and a composite member with topping concrete placed on top of the PC unit. The projecting height of the shear reinforcement truss bar was sufficiently secured and rough surface treatment was applied to the upper part of the PC unit to ensure interfacial horizontal shear performance with the topping concrete. Figure 1: Concept of an optimized-section precast slab with structural aesthetics (OPS). This study mainly aimed to verify the structural performance of OPS and to examine the validity of the current design codes. An experimental study was conducted to investigate the flexure and shear behavior of the PC unit specimens and the composite PC specimens with topping concrete that were designed according to the ACI 318-14 [16] and KCI 2012 [17] codes. To achieve this goal, a framework was also established, as shown in Figure 3, in which the study is summarized with the three phases. Firstly, as described in the introduction, the existing PC slabs were reviewed and the OPS slab system was introduced with an emphasis on the basic concept and the novelty of the OPS. In the next stage, the experimental study was designed and was conducted to investigate the flexure and the shear behavior of the OPS. The test results are then discussed and are compared with the current design codes and non-linear analysis results.