# Experimental Study on an Optimized-Section Precast Slab with Structural Aesthetics
## 3 Test Results and Discussion  
### Load Deflection Responses and Failure Patterns  
Figure 9 shows the load-deflection responses of the specimens. Figure 9a shows the vertical deflections that were measured from the LVDTs shown in Figure 9a,b for the UF and CF specimens. The initial flexural cracks occurred at 61 and 85 kN, respectively in the UF and CF specimens, and the difference is because the member height and the moment of inertia of the CF specimen were greater due to the topping of concrete. After the flexural cracks, the two specimens showed a reduction in stiffness and exhibited ductile behavior until failure. Figure 10 shows that both the UF and CF specimens revealed typical flexural failure modes. However, in the CF specimen, which was a composite PC slab member, a slightly larger deflection was measured in the LVDT that was located on the right after the maximum load was reached, and the failure occurred as the critical crack between the right loading point and the tension zone progressed. The US and CS shear specimens were divided into USa, USb, CSa, and CSb based on the results of the experiments that were conducted at the left and the right ends of the members, as shown in Figure 8b,d, and Figure 9b shows their load-deflection curves. In the USa and USb PC unit specimens, the initial shear cracks occurred at the 85 and 72 kN loads, respectively. The USa and USb specimens, which were PC unit members, were observed to have developed critical cracks around the variable cross-section, where the positions of the top and bottom flanges changed. In addition, due to the influence of the variable cross-section, a relatively high crack angle was observed, as cracks were concentrated on the web between the loading point and the variable cross-section, as shown in Figure 11a,b, which is different from general shear crack patterns. In the CSa and CSb composite PC specimens, the initial flexural cracks were observed at loads of 109 and 133 kN and shear cracks occurred in the member web at the loads of 186 and 195 kN, respectively. After reaching the maximum load, the CS specimens that were composite PC members showed more brittle behavior compared to the US specimens that were non-composite PC units. This suggests that as the flexural performance was improved due to the topping concrete and as the influence of the variable cross-section was relatively small in the composite PC members (i.e., the CSa and CSb specimens), the shear dominant failure pattern seemed to be more apparent compared to the PC unit specimens, as shown in Figure 11c,d. Figure 11: _Cont_. Figure 10: Failure crack patterns of the flexural specimens. Figure 9c shows the load-deflection responses of the NFW specimens. Figure 12 shows that the region of the NFW specimen can be divided into Section 1 where the compression flange was formed in the section where the longitudinal tensile reinforcement was placed (moment strength in this section: \(M_{n}=M_{n1}\)); Section 2, where the longitudinal tensile reinforcement was placed, but the compressive force is resisted by the rib section without a compression flange (moment strength in this section: \(M_{n}=M_{n2}\)); and Section 3, where there was no longitudinal tensile reinforcement, and the compressive force is resisted by the rib section (moment strength of cross-section in this section: \(M_{n}=M_{n3}\)). Figure 13a,b show that the failure section of the NFW specimen was located at a distance 1425 mm from the center of the member, not at the maximum-moment region. This is because the flexural failure occurred at the section with the lowest moment strength (i.e., \(M_{u}=M_{n3}\)) before the external moment (\(M_{u}\)) that was caused by one-point loading reached the maximum moment capacity (i.e., \(M_{u}=M_{n1}\)), as shown in Figure 12. The failure section of the NFW specimen also coincided with the location where the 5-D19 tensile rebars were cut as well as the location of the variable cross-section, as mentioned earlier.