# Flexural Strength of Composite Deck Slab with Macro Synthetic Fiber Reinforced Concrete
## 4 Test Results
### Strain Distribution of a Section  
To evaluate the flexural strength of the deck plate reinforced with MFRC in the positive moment region, it was necessary to assess the strain distribution and determine whether the deck yielded over the entire area. For this, the strain distribution at the center of the section was confirmed and is shown in Figure 11. The strain gauge was attached to the web in the center of the specimen. Each gauge was attached to the bottom surface of the specimen, the rib of the deck, the upper part of the deck, and the concrete compression fiber.  
The neutral axis depth of P-Deck-F2.4 was larger than that of P-Deck-F0, and the strain at the bottom of the deck was smaller than that of the F0 specimen. This is because MFRC partially resists tensile force according to the amount of macro-synthetic fiber incorporated. In the P-Deck F2.4S specimen, the strain of the steel deck bottom was much greater than that of the other two specimens. This is because the MFRC and steel deck plate were completely composited by studs. Since most of the deck cross-sectional area yielded, it can be assumed that the tensile force of the deck plate acted in the centroid when the flexural strength was calculated.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Theoretical Value**} & \multicolumn{4}{c}{**Test Results**} \\
**ID** & \(P_{cr,eal}\) & \(P_{cr,test}\) & \(P_{cr,sw}\) & \(\Delta_{cr,test}\) & \(p_{cr,coal}\) \\  & **(kN)** & **(kN)** & **(kN)** & **(mm)** & \(p_{cr,sal}\) \\ \hline P-Deck-0 & & 4.85 & 14.02 & 1.85 & 1.15 \\ P-Deck-F2.4 & 12.17 & 6.26 & 15.43 & 2.37 & 1.27 \\ P-Deck-F2.4S & & 7.98 & 17.15 & 5.01 & 1.41 \\ \hline N-Deck-P0-R0.91 & & 6.07 & 15.24 & 2.47 & 1.86 \\ N-Deck-F2.4-R0.91 & & 5.85 & 15.02 & 2.71 & 1.83 \\ N-Deck-F2.4-R0.65 & & 3.47 & 12.64 & 1.37 & 1.54 \\ N-Deck-F2.4-R0.39 & & 2.26 & 11.43 & 1.03 & 1.39 \\ \hline \hline \end{tabular} \(P_{cr,sel}\): cracking load, \(P_{cr,tel}\): cracking load at initial flexural crack, \(P_{cr,sw}\): cracking load considering self-weight of specimen, \(\Delta_{cr,tel}\): displacement at initial flexural crack.  
\end{table}
Table 8: Test results of cracking load.  
When a load was applied to the negative moment region of the steel deck, it did not significantly affect the flexural strength because the deck plate resisted the compressive force. Therefore, the upper tensile reinforcements were considered only when calculating the flexural strength. The load-strain relationship is shown in Figure 12 to confirm whether the rebar yielded at the point of maximum strength.  
The upper tensile reinforcement of all specimens yielded, and the N-Deck-F2.4-R0.39 with minimum reinforcement ratio yielded at the point of maximum strength.  
As a result of comparing the R0.91 series specimens at the same reinforcement ratio, as the F2.4 specimen approached the ultimate strength, it showed less tensile strain compared to that at the same load. This is because the MFRC partially resisted the tensile force of the rebar.  
Figure 11: Strain distribution at the center of specimens (unit: mm).  
Figure 12: Load–strain relationship (negative moment test specimens; unit: mm).