# Flexural and Shear Performance of Prestressed Composite Slabs with Inverted Multi-Ribs
## 3 Experimental Results
### Load-Deflection Responses  
Figure 5 shows the load-deflection curves of UF and CF specimens, and Table 2 summarizes the test results. In the UF specimen, which is a PC unit slab, the initial flexural crack was observed at a load of about 70 kN (\(M_{cr}=100.0\) kN\(\cdot\)m). Later, flexural failure occurred as the concrete on the compression side in the upper part of the rib was crushed at a load of 96.2 kN (\(M_{u}=125.1\) kN\(\cdot\)m). In the CF specimen, which is a composite member, flexural cracks were observed at a load of 147 kN (\(M_{cr}=191.5\) kN\(\cdot\)m). Then, the stiffness of the specimens continued to be reduced, and flexural failure occurred at a load of 267.1 kN (\(M_{u}=347.2\) kN\(\cdot\)m). The UF specimen showed slightly less ductility than the CF specimen; although the compressive force generated by the flexural moment should be resisted by the ribs in a UF specimen, the rib is very small narrow to the overall width of the member, as shown in Figure 2a, so that the position of the neural axis is relatively low.  
Figure 4: Crack patterns of test specimens at failure; (**a**) UF specimen; (**b**) CF specimen; (**c**) USt specimen; (**d**) USt specimen; (**e**) CSt specimen; (**f**) Csf specimen.  
Figure 6 shows the load-deflection curves of the USt, USf, CSt, and CSf specimens. In the USt specimen tested in the transfer length zone of the PC unit slab, shear cracks were observed at a load of about 151 kN (\(V_{cr}=121\) kN), and shear failure occurred at a load of 291 kN (\(V_{u}=233\) kN). In the USt specimen tested in the strain plateau zone of the PC unit slab, the initial shear crack occurred at a load of about 170 kN (\(V_{cr}=136\) kN). Even after that, new shear cracks were formed, as shown in Figure 4d, and shear failure occurred at a load of 326 kN (\(V_{u}=261\) kN). However, unlike the USt specimen, there was no decrease in the stiffness of the member, even after shear cracking, in the USf specimen. On the CSt specimen, which is a composite member, flexural cracks around the loading point developed into inclined shear cracks at a load of about 370 kN (\(V_{cr}=284\) kN), and shear failure took place as the horizontal crack towards the support along the interface between the PC unit slab and cast-in-place concrete occurred at a load of 548 kN (\(V_{u}=420\) kN). In the CSf specimen, the initial inclined crack was observed at a load of 420 kN (\(V_{cr}=322\) kN), and shear failure took place as the horizontal crack towards the support occurred at a load of 849 kN (\(V_{u}=651\) kN) similarly to that in the CSt specimen. As can be seen from the test results, the shear cracking strength (\(V_{cr}\)) and ultimate shear strength (\(V_{u}\)) of the USf and CSf specimens tested in the strain plateau zone, where the effective prestress (\(f_{se}\)) is fully developed, were found to be greater than those of the USf and CSt specimens, respectively.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Specimen** & **Failure Mode** & \begin{tabular}{c} **Failure Loads** \\ **(\(P_{u}\), kN)** \\ \end{tabular} & \
\begin{tabular}{c} **Flexural Strength** \\ **(\(M_{u}\), kN\(\cdot\)m)** \\ \end{tabular} &
\begin{tabular}{c} **Shear Strength** \\ **(\(V_{u}\), kN)** \\ \end{tabular} \\ \hline UF & Flexure & 96.2 & 125.1 & - \\ \hline CF & Flexure & 267.1 & 347.2 & - \\ \hline USt & Shear & 291.0 & - & 232.8 \\ \hline USt & Shear & 325.6 & - & 260.5 \\ \hline CSt & Shear & 548.0 & - & 420.1 \\ \hline CSf & Shear & 848.8 & - & 650.7 \\ \hline \end{tabular}
\end{table}
Table 2: Summary of test results.  
Figure 5: Load-deflection responses of flexural test specimens.