# Flexural Strength of Composite Deck Slab with Macro Synthetic Fiber Reinforced Concrete
## 4 Test Results  
### Crack Propagation and Failure Modes  
In the bending tests of the deck plate slabs reinforced with MFRC, all specimens showed flexural failure patterns (Figures 8 and 9). In the P-Deck-F0, an initial flexural crack occurred at a load of about 5 kN. Subsequently, as greater load was applied, a crack appeared, indicating shear-bond failure at the location of the deck rib height of 78 mm. This behavior was typical of partial-composite action, which occurs if the horizontal shear-transfer device is not effective enough for the steel deck and concrete to act as a unit without the occurrence of slip [25, 29, 30, 31]. After that, the deck plate buckled and was fractured by the crushing of concrete. Figure 8: Crack and failure patterns (positive moment test specimens). Figure 7: Test setup (unit: mm). In the P-Deck-F2.4 specimen, the initial flexural crack occurred later than in P-Deck-F0. In addition, the shear-bond failure pattern occurred in P-Deck-F0, but the crack width and length were small. The spacing of the flexural cracks in P-Deck-F2.4 was shorter than that of P-Deck-F0. This indicates that the macro-synthetic fiber was effective in crack control. After that, local buckling of the deck plate occurred at the loading point as in the P-Deck-F0 specimen, and the experiment ended with the crushing of concrete. P-Deck-F2.4S was designed to confirm the flexural behavior of the deck plate and concrete in complete composite action. The initial crack in the specimen was not visually significantly different from that of P-Deck-F2.4. Therefore, the exact initial cracking point was determined as the point at which the strain of the deck plate increased rapidly and the point at which the slope of the load-displacement relationship graph rapidly changed. This confirmed that cracks occurred later than in P-Deck-F2.4, and no shear-bond failure occurred between the deck plate and concrete. This means that a stud was required for complete composite action between the steel deck and concrete. The spacing of the flexural cracks was similar to that of P-Deck-2.4, and fracture occurred after crushing of the upper concrete. The N-series specimen tests were performed with a three-point loading test, and flexural failure occurred in all the specimens. The failure patterns of the specimens are shown in Figure 9. The average crack spacing of the N-Deck-F2.4-R0.91 specimen was 18 mm shorter than that of the N-Deck-F0-R0.91 specimen with the same reinforcement ratio. In the N-Deck-F2.4-R0.65 and N-Deck-F2.4-R0.39 specimens with less reinforcement, flexural failure also occurred. As the reinforcement ratio decreased, the crack gaps widened. In particular, in N-Deck-F2.4-R0.39 with the minimum reinforcement ratio, the crack spacing was quite wide, but the displacement ductile ratio was 13.5, showing a ductile failure pattern. The test results and the load-displacement relationships are shown in Table 7 and Figure 10, respectively. The yield point of each specimen was calculated as the point at which the bottom of the deck plate or tensile reinforcement reached the yield strain. The cracking load was determined based on the first point of decrease in initial stiffness in the load-deflection relationship and the point at which the deformation rate of the deck plate and reinforcement rapidly increased, and the results are shown in Table 8.  
Figure 9: Crack and failure patterns (negative moment test specimens).