# Flexural Strength of Composite Deck Slab with Macro Synthetic Fiber Reinforced Concrete
## 4 Test Results
### Crack Propagation and Failure Modes
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**ID**} & \multicolumn{3}{c}{**Theoretical Value**} & \multicolumn{3}{c}{**Test Results**} \\  & \(P_{n}\) & \(\Delta_{y}\) & \(P_{y}\) & \(P_{max,test}\) & \(P_{max,sw}\) & \(P_{max,sw}\)/\(P_{n}\) & \(\Delta_{max}\) & \(\mu_{\Delta}\) \\  & **(kN)** & **(mm)** & **(kN)** & **(kN)** & **(kN)** & **(mm)** & **(mm)** & **(mm)** \\ \hline P-Deck-0 & & 36.52 & 30.44 & 49.09 & 58.26 & 0.87 & 204.86 & 5.61 \\ P-Deck-F2.4 & 66.67 & 35.54 & 30.79 & 51.31 & 60.48 & 0.91 & 204.04 & 5.74 \\ P-Deck-F2.4S & & 26.80 & 26.78 & 69.82 & 78.99 & 1.18 & 225.16 & 8.40 \\ \hline N-Deck-F0-R0.91 & & 32.04 & 30.39 & 40.95 & 50.12 & 1.28 & 288.97 & 9.02 \\ N-Deck-F2.4-R0.91 & & 26.83 & 30.18 & 44.23 & 53.40 & 1.37 & 306.46 & 11.42 \\ N-Deck-F2.4-R0.65 & 28.52 & 23.24 & 21.48 & 33.8 & 42.97 & 1.51 & 288.34 & 12.41 \\ N-Deck-F2.4-R0.39 & 17.50 & 21.65 & 12.39 & 19.09 & 28.26 & 1.62 & 291.35 & 13.46 \\ \hline \hline \end{tabular} \(P_{n}\): nominal flexural load, \(P_{y}\), \(\Delta_{y}\): yield load and deflection when bottom deck (rebar) strain reached yield strain, \(P_{max,sw}\): modified maximum load considering weight of the specimen, \(\Delta_{max}\): displacement at \(P_{max}\), \(\mu_{\Delta}\): displacement ductility.  
\end{table} 
Table 7: Test results of ultimate flexural load. Figure 10: Load–displacement relationships. The tensile strength of the macro-synthetic fibers was not considered when calculating nominal flexural strength \(P_{n}\) because the calculation assumed complete composite of steel deck and concrete, and the entire section of the deck yielded [20,29]. Similarly, calculating the cracking load \(f_{r}\) did not consider the effect of the macro-synthetic fiber. The calculation and test results were compared considering self-weight, as discussed below. In the P-Deck-F0 and F2.4 specimens, maximum strength increased with macro-synthetic fiber content. The deflection at maximum load was similar between the two specimens, but the F0 specimen showed a rapidly decreased load after the maximum load. In contrast, the F2.4 specimen slowly decreased in moment resistant capacity after maximum load. To confirm the initial crack, the graph was enlarged and analyzed (Figure 10b,d). The initial cracking load increased as macro-synthetic fibers were incorporated, confirming that macro-synthetic fibers can improve crack strength and increase effective flexural stiffness. In the negative moment test, in the R0.91 series specimen with a reinforcement ratio of 0.91%, the flexural strength increased as macro-synthetic fibers were incorporated. As the reinforcement ratio decreased, the value of \(P_{max,sw}/P_{n}\) increased. According to ACI 318-19 [20] and ASCE standard specifications [29], the flexural strength conservatively evaluates the actual strength, so the residual strength of MFRC should be considered when calculating flexural strength. There was no significant difference in the cracking point of the negative moment region due to macro-synthetic fiber dosage. However, when macro-synthetic fiber is mixed, it has greater flexural stiffness at yield. Thus, it is expected that MFRC will have greater effective flexural stiffness, as in the positive moment test.