## 4 Experimental Results and Discussions
### Flexural Performance of Concrete Pedestrian Decks  
2.1 Effects of End-Hook Geometry and Volume Fraction of Hooked-End Steel Fibers on the Overall Flexural Behavior  
The flexural load versus center deflection curves for all concrete pedestrian decks tested are shown in Figure 7. Given the same fiber volume fraction, the 5D hooked-end fibers have the best flexural performance including the load-carrying capacity and post-peak ductility, followed by the 4D and 3D hooked-end fibers, respectively. This is mainly caused by their better pullout resistance, i.e., higher bond strength and pullout work, as reported by some previous studies [10; 11; 12]. The higher number of hook ends requires a higher force to bend more plastic hinges; hence, the 5D hooked-end fiber had the highest pullout resistance, followed by the 4D and 3D fiber, based on an assumption that the cement matrix was strong enough. [PERSON] et al. [11] reported that the tensile strength and post-cracking hardening behavior of concrete are enhanced by adding 0.5% and 1% hooked-end steel fibers and the 5D hooked-end fiber results in the best tensile performance. Given the identical fiber volume fractions of 0.5% and 1%, only the specimens with 5D hooked-end fibers exhibited a re-increase in the tensile stress after cracking, called hardening, while the others with 3D and 4D hooked-end fibers did not show the hardening behavior. Similarly, [PERSON] et al. [12] mentioned that SFRCs comprising fibers with multiple hook ends provide a higher residual flexural strength than the counterpart with a single hook end (3D) because of the enhanced fiber anchorage. Thus, it can be concluded that a higher number of hook ends can effectively increase both the flexural tensile strength and post-cracking bridging capacity, related to the residual strength, of plain concrete compared to a lower number of hook ends. Figure 6: Relationship between flexural strength and fiber volume fraction: (**a**) 3D fiber, (**b**) 4D fiber, (**c**) 5D fiber. Similar to the uniaxial flexural test results of notched beams, the SFRC decks with 0.37% volume fraction exhibited deflection-softening behaviors. This means that the post-cracking maximum load is lower than the initial cracking load, as shown in Figure 7a. Furthermore, a sudden drop in the load immediately after the crack formation was observed similar to the results observed by [PERSON] and [PERSON] [28]; it is caused by the drastic softening of plain concrete and vulnerable fiber bridging capability. The slight re-increase in flexural load after the sudden decrease was also reported by [PERSON] et al. [1] at low volume fractions of steel fibers. At the fiber volume fraction of 0.6%, the 3D hooked-end fiber specimen led to deflection-softening behavior, whereas the 5D hooked-end fiber specimen resulted in deflection-hardening behavior. The 4D hooked-end fiber specimen led to an intermediate behavior. Regardless of the fiber type, all SFRC decks with \(v_{f}\) of 0.6% prevented or at least decreased the sudden load drop immediately after the formation of crack based on the enhanced fiber bridging capacity. The steep decrease in the post-cracking flexural load was fully sustained by the higher number of steel fibers at the crack surface, leading to the improved residual strength in SFRC decks with the higher fiber volume fraction of 0.6% compared to those with lower volume fractions, as shown in Figure 7a,b. With the highest fiber volume fraction of 1.0%, all SFRC decks showed excellent deflection-hardening behaviors, as shown in Figure 7c. Since using a higher number of hook ends is more effective in enhancing the flexural performance of concrete decks as compared to a lower number, it can more effectively reduce or replace the minimum amount of steel rebars, based on ACI 318 code [3]. The flexural strength of SFRC decks increased with an increase in the fiber volume fraction from 0.37% to 1.0%, for all steel fiber types, which is consistent with the findings of [PERSON] et al. [12].