# Flexural and Shear Performance of Prestressed Composite Slabs with Inverted Multi-Ribs
## 5 Conclusions  
In this study, experimental and analytical research has been performed to evaluate the flexural and shear performance of the half-precast concrete slab with inverted multi-ribs (Joint Advanced Slab, JAS). The crack patterns, load-deflection responses, and strain behavior of the longitudinal and shear  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Specimen**} & \multirow{2}{*}{
\begin{tabular}{c} **Test Results** \\ **(\(V_{w}\), kN)** \\ \end{tabular} } & \multicolumn{3}{c}{**Calculation Results (\(V_{w}\), kN)**} \\ \cline{2-5}  & & \(V_{w1}\) **(Ratio, \(V_{w}/V_{n1}\))** & \(V_{n2}\) **(Ratio, \(V_{w}/V_{n2}\))** & \(V_{n3}\) **(Ratio, \(V_{w}/V_{n3}\))** \\ \hline USt & 232.8 & \multicolumn{3}{c}{\(115.9\) (2.01)} \\ \hline USt & 260.4 & \multicolumn{3}{c}{\(223.9\) (1.16)} \\ \hline CSt & 420.3 & 504.8 (0.83) & 452.7 (0.93) & 364.7 (1.15) \\ \hline CSt & 651.2 & 655.9 (0.99) & 551.7 (1.18) & 364.7 (1.78) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comparison of shear strengths.  
Figure 11: Comparison of the test and analysis results on the shear specimens; (**a**) Non-composite members; (**b**) Composite members.  
reinforcement of the specimens were measured and analyzed in detail, and the flexural and shear performance of the JAS was quantitatively evaluated using a non-linear flexural analysis method and ACI 318-14 code. In addition, a design method that can most reasonably estimate the shear strength of the JAS was proposed based on the test results. On this basis, the following conclusions can be drawn:  
1. The UF specimen, a PC unit slab, exhibited a ductility slightly lower than that of the CF specimen with cast-in-place concrete; although the compressive force generated by the flexural moment should be resisted by the ribs, the rib is much narrower than the overall width of the member, and thus the position of the neural axis is relatively low.
2. The non-linear flexural analysis provided very approximate evaluations of the flexural behavior and strength of the JAS, regardless of the presence of cast-in-place concrete, and thus can be applied to the flexural design of the JAS.
3. The shear test results showed that the lattice reinforcement placed in composite specimens exhibited effective shear resistance performance, whereas the lattice reinforcement placed in PC unit specimens did not make a significant contribution to the shear resistance of the member. Therefore, the shear design results of the safe side can be obtained without considering the contribution of shear reinforcement (\(V_{s}\)) in the design of the PC unit slab.
4. The shear crack angle observed in composite specimens was about 60\({}^{\circ}\), which was steeper than that observed in the general PSC member. In addition, various methods for estimating the shear contributions of the PC unit and cast-in-place concrete were examined based on the ACI 318-14 code. The results confirmed that a method of calculating the contribution of shear reinforcement (\(V_{s}\)) by applying the crack angle (\(\beta\)) of 60\({}^{\circ}\), and estimating the PC unit shear contribution (\(V_{cw}\)) by regarding the distance from the top of the PC unit rib to the center of the strands layer as the effective depth (\(d_{p}\)) of the composite member, while estimating the shear strength by considering the remaining part as RC, provides the most reasonable analysis results.  
Original draft manuscript--S.-J.H.; Validation--J.-H.J. and H.-E.J.; Investigation--S.-H.C. and S.C.; Supervision and Review Writing--K.S.K.  
This research received no external funding.  
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2019R1A2C2086388).  
The authors declare no conflict of interest.