# Flexural and Shear Performance of Prestressed Composite Slabs with Inverted Multi-Ribs
## 1 Introduction  
The precast concrete (PC) slab has many advantages in terms of the quality control of concrete through prefabrication at the factory, reduction of construction costs by shortening the construction period, and reduction of waste on construction sites [1; 2; 3]. Accordingly, various types of half-PC slab members, such as the flat precast slab, hollow-core slab, multi-rib slab, and double-tee slab, have been developed, and related research on them has been actively done. The flat precast slab has the advantage of ensuring easy mold operation and rebar placement. However, because of the thin flanges, it requires temporary work, such as the installation of shores, to resist the construction load at the time of casting topping concrete [4; 5]. The hollow-core slab can reduce the lifting weight because of the presence of hollows in the cross-section and can greatly increase the thickness of the cross-section under design conditions in which a load is quite large [3; 6; 7; 8]. However, the hollow-core slab manufactured using an extruder is very vulnerable to web shear at the end of the member because shear reinforcementcannot be placed on the web [3; 9; 10]. Furthermore, since the ACI 318-14 code [11] prescribes that the web shear strength of a one-way prestressed member that exceeds 315 mm in thickness and has less than the minimum shear reinforcement shall be reduced by half, the application of the hollow-core slab produced by the extrusion method can provide non-economical design results [3; 10]. Meanwhile, the multi-rib and double-tee slabs have cross-sectional shapes that are very efficient for positive moment resistance because of the removal of an unnecessary concrete section on the tension side. However, there is a disadvantage in that the top flange is very thin, making it difficult to achieve continuity at the member ends [12; 13; 14].  
In order to maximize the advantages of the half-PC system, a joint advanced slab (JAS) to minimize the temporary work process and lifting weight during construction, and facilitate the placement of shear reinforcement, has recently been developed, as shown in Figure 1. The JAS has advantages, in that it has greater flexural stiffness of the cross-section than that of the flat precast slab because of the presence of inverted multi-ribs, and it can minimize the on-site rebar placement process, because the shear keys introduced at both ends of the slab panel replace the reinforcing steel required for connections between PC slabs. In addition, the introduction of prestressing into the cross-section improves the flexural and shear performance of the member, and the N-type lattice reinforcement is placed in the ribs as a stirrup to resist horizontal and vertical shear forces effectively. Moreover, since the JAS ensures continuity at the end region of the slab, it can resist the entire static moment generated by the load applied after the placement of cast-in-situ concrete by dividing it into positive and negative moments.  
In this regard, experimental research was done to examine the flexural and shear performance of the newly developed JAS, where the presence of cast-in-place concrete and the location of the critical section were set as the main test variables. For the flexural specimens, the strain gauges were attached to the longitudinal tension reinforcement and concrete in a compression zone and were attached to the stirrups for the shear specimens. Then, the member behavior, according to the loads, was measured and analyzed in detail. In addition, this study quantitatively evaluated the flexural and shear performance  
Figure 1: Characteristics of the joint advanced slab (JAS).  
of the JAS by comparing the test results and analysis results from the non-linear flexural analysis model and structural design codes. In particular, based on the shear test results, a method to reasonably estimate the shear contributions of the PC unit and cast-in-place concrete was proposed for the shear design of the JAS.