# Flexural Strength of Composite Deck Slab with Macro Synthetic Fiber Reinforced Concrete
## 1 Introduction  
As more buildings are becoming high-rise, composite slab systems using deck plates are being applied to improve constructability, reduce construction time, and address economic feasibility. Deck plates are categorized as either formwork or structural deck plates, depending on the usage. The structural deck plate has advantages that the deck plate itself acts as a formwork when pouring concrete and does not require temporary work such as props. In addition, when a structural deck plate is permanent, it can resist tensile force without reinforcement. However, in slabs such as steel decking, the reinforcement ratio is low, and a larger area is exposed to air than in other structural members. This can cause wide cracks in a building. Additionally, cracks occur in a slab for various reasons, such as shrinkage and creep. To prevent this, only shrinkage and temperature reinforcement bars are placed on top of the deck plate. However, additional reinforcing bars increase construction time, process, and costs. Moreover, when a structural deck plate is constructed as a continuous span, the wire mesh used as the upper rebar is cold-formed and allows very little elongation. The member will not have sufficient ductility because it has less than the minimum reinforcement ratio. Therefore, one method for preventing upper cracks in a slab and improving the flexural performance of the negative moment region of the deck plate is to apply fiber-reinforced concrete. Fibers incorporated for crack control are generally reinforced with microfibers, such as steel fiber, glass fiber, and polypropylene; all of these fibers show excellent crack control [1]. Therefore, since an upper reinforcing bar is not required, workability increases, process steps are reduced, and economic efficiency is improved. Structural performance is improved because the tensile strength is increased, and deflection can be reduced by improving effective flexural stiffness. The flexural strength increase reduces the upper tensile reinforcement in the negative moment region. However, if the size of a microfiber crack increases to a macro level, the fiber is pulled out, and the bridge effect decreases, resulting in a rapid decrease in fiber performance [2; 3]. Interest in macro fibers with large diameters and long lengths is increasing as they may present a solution to the problems of microfibers. Macro fibers are specified as being at least 0.022 mm in diameter and 38 mm in length; fibers of smaller size are microfibers [4]. A previous study [2; 5] showed that concrete containing macro fibers maintained high tensile strain and tensile strength above a certain level, even with large crack widths. [PERSON] et al. [6] and [PERSON] et al. [7] reported that when macro-synthetic fiber is incorporated into concrete, the ultimate compressive strain increases with the macro-synthetic fiber dosage. In addition, it is reported that the flexural tensile strength and residual strength increase as the fiber dosage increases. According to another study [8], introducing macro fiber into reinforced concrete slabs is effective in controlling cracks, reducing deflection, and improving flexural strength. Therefore, in this research, crack patterns and flexural strength were evaluated using macro-synthetic fiber-reinforced concrete (MFRC) in structural steel deck plates. According to the previous research [6], MFRC is effective in improving the flexural strength, and the method of quantitatively evaluating the flexural strength of MFRC without reinforcement using the residual strength improved by macro-synthetic fiber is proposed. In addition, according to previous study [9], when applying steel fiber-reinforced concrete to a structural deck plate, it is possible to simplify the process and improve structural performance by replacing the upper temperature reinforcement.