## 3 Experimental Work
### Experimental Setup  
Slabs that are 3000 and 3500 mm long were supported over spans of 2500 and 3000 mm, respectively. Two concentrated loads were placed symmetrically on the slabs 700 mm apart (Figure 3). A 10 mm thick soleplate designed to prevent bearing failure was installed at the point of contact between the specimen and the roller support.  
Crack widths were measured close to the bottom side surface of the RC slabs using an optical crack width gauge with a least count of 0.01 mm (0.4 mils). Crack widths were measured within the constant moment region. The load values that produced crack widths of 0.3 and 0.5 mm (12 to 20 mils) were recorded and used to calculate the rebar stress in the tensile section by cracked transform section analysis. Each bar stress was further used to estimate the crack widths with Equation (1). Most of the slabs had three to four cracks forming in the constant moment region at the load that produced the first 0.3 mm (12 mils) crack and had two to three additional cracks formed at the failure of the slab specimen outside the constant moment region. As shown in Figure 4, SA-H16-PR-2 has 4 cracks at the load that produced the 1 st 0.3 mm crack. At failure, the crack widths of the 4 cracks in the constant moment region became much wider with three additional cracks  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{6}{c}{**Specimens**} \\ \cline{2-7}  & **SA-H16** & **SA-H19** & **SA-H22** & **SA-H25** & **SH-H19** & **SK-H22** \\ \hline Number of specimens & 6 & 6 & 2 & 2 & 4 & 4 \\ \(d_{d}\) (mm) & 80 & 80 & 80 & 80 & 80 & 80 \\ \(a\) (mm) & 160 & 160 & 160 & 160 & 260 & 360 \\ \(d_{c}\) (mm) & 60 & 60 & 60 & 60 & 60 & 60 \\ \(h\) (mm) & 300 & 300 & 300 & 300 & 400 & 500 \\ \(d\) (mm) & 240 & 240 & 240 & 240 & 340 & 440 \\ \(L\) (mm) & 3000 & 3000 & 3000 & 3000 & 3000 & 3500 \\ Rebar diameter (mm) & 16 & 19 & 22 & 25 & 19 & 22 \\ Tensile reinforcement ratio (\%) & 0.41 & 0.60 & 0.81 & 1.06 & 0.59 & 0.62 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Dimensions of RC slab specimens.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{6}{c}{**Specimens**} \\ \cline{2-6}  & **SA-H16** & **SA-H19** & **SA-H22** & **SA-H25** & **SH-H19** & **SK-H22** \\ \hline Experimental data (MPa) & 31.5, 34.2, & 30.3, 32.5, & 33.4, 32.3, & 30.1, 31.5, & 33.7, 32.1, \\  & 35.2 & 34.4 & 32.2 & 28.6 & 31.5 \\ \hline Average strength (MPa) & 33.7 & 32.4 & 32.6 & 30.1 & 32.4 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Concrete compressive strength.  
formed outside the constant moment region prior to failure. Similarly, for SH-H19-PR-2, 4 cracks appeared at the load that produced the first 0.3 mm crack within the constant moment region, and two additional cracks formed outside the constant moment region at failure. Figure 4 shows that the crack widths observed in SH specimens that have tighter bar spacing are smaller compared to the SA specimens, which have larger bar spacing. This is a typical behavior observed in RC members with smaller bar spacing where the bond between steel reinforcement and concrete is better and more cracks with smaller crack widths are generated than the case with larger bar spacings. To distinguish the cracks of 0.3 mm width, which are not easily visible in these pictures, red-colored dash lines are drawn next to the cracks.