# Shear Tests of Deep Hollow Core Slabs Strengthened by Core-Filling
## 2 Test Program  
In this study, five PHCS specimens with a thickness of 400 mm were fabricated as shown in Table 2 and Figure 1. The width of the PHCS unit (\(b\)) was 1200 mm, the width of one web (\(b_{w1}\)) was 55.2 mm, the total width of the web (\(b_{w}\)) was 276 mm, and the void ratio was 56%. Eleven prestressing strands with a diameter of 12.7 mm were placed in the lower part of the section, while three 9.5 mm diameter strands were laid in the upper part of the section, to control the tensile stress generated during the introduction of prestress. As shown in Table 2, the first character in the names of the specimen indicates a shear reinforcement ratio (\(\rho_{v}\)). NR is a specimen without shear reinforcement. LR means a specimen with a relatively low \(\rho_{v}\) (i.e., \(\rho_{v}=0.175\%\)), while HR means a specimen with a relatively high \(\rho_{v}\) (i.e., \(\rho_{v}=0.395\%\)). The number that follows is the ratio of the number of filled cores to the number of entire cores. For example, LR-2/4 represents a specimen in which two of the four voids are filled with normal strength concrete. The tensile strength (\(f_{pu}\)) of the prestressing strands used in the specimens was 1860 MPa, and the effective prestress introduced into the PHCS unit was approximately 1200 MPa, which was about 65% of \(f_{pu}\). Figure 1b-d shows that the top flanges were opened, and in-filled concrete was casted in the specimens, except for the reference specimen (NR-0/4). In addition, as shown in Figure 2, the core-filling concrete was placed for the position of the section, which is up to 1500 mm away from both ends of the member. Table 3 shows the mix proportions of the PHCS unit and the core-filling concrete. The concrete compressive strengths of the PHCS unit (\(f_{c,pc}\)) and filled cores (\(f_{c,core}\)) were 66.0 and 25.1 MPa, respectively, which were measured from cylinder tests. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Designation** & \(b_{w}\) **(mm)** & \(h\) **(mm)** & \(d_{p}\) **(mm)** & **Number of Filled Cores** & \(\rho_{v}\)**(\%)** \\ \hline NR *—/0/4 ** & & & & 0 & 0.0 \\ NR *—/2/4 ** & & & & 2 & 0.0 \\ NR *—/4/4 ** & 276 & 400 & 360 & 4 & 0.0 \\ LR *—2/4 ** & & & & 2 & 0.175 \\ HR *—2/4 ** & & & & 2 & 0.395 \\ \hline \hline \end{tabular}  
* Shear reinforcement ratio (NR: Non-Reinforced, LR: Low Reinforced, HR: High Reinforced). ** Ratio of number of filled cores to number of entire cores.  
\end{table} 
Table 2: Details of test specimen. Figure 1: Section details of test specimens. (**a**) NR—0/4 specimen. (**b**) NR—2/4 specimen. (**c**) NR—4/4 specimen. (**d**) LR—2/4 and HR—2/4 specimens. Figure 3 shows the details of helix shear reinforcement in LR-2/4 and HR-2/4 specimens. The amount of shear reinforcement was determined to be more than the minimum shear reinforcement ratio (\(\rho_{v,\text{min}}\)) specified in ACI 318-14 [16], where \(\rho_{v,\text{min}}\) was calculated as below:  
\[\rho_{v,\text{min}}=\frac{0.0625\sqrt{f_{c,pc}}}{f_{yt}}\geq\frac{0.35}{f_{yt}}, \tag{1}\]  
where, \(f_{yt}\) is the yield strength of the shear reinforcement, which was 400 MPa. The minimum shear reinforcement ratio (\(\rho_{v,\text{min}}\)) calculated using Equation (1) was 0.127%, and the diameters of shear reinforcements placed in LR-2/4 and HR-2/4 specimens were 8 and 12 mm, which correspond to the reinforcement ratios (\(\rho_{v}\)) 0.175% and 0.395%, respectively. \begin{table}
\begin{tabular}{l c c c c c c} \hline
**Concrete** & \(a_{g,\text{max}}\) **(mm)** & **S/a (\%)** & **W/C (\%)** & **W (kg/m\({}^{3}\))** & **C (kg/m\({}^{3}\))** & **S (kg/m\({}^{3}\))** & **G (kg/m\({}^{3}\))** \\ \hline PHCS unit & 20 & 35.5 & 36.1 & 130 & 360 & 699 & 1264 \\ Core-filling & 25 & 47.5 & 47.8 & 170 & 356 & 848 & 956 \\ \hline \end{tabular}  
* Notations: S/a: percentage of fine aggregate, W/C: water-cement ratio, W: water, C: cement, S: fine aggregate, G: coarse aggregate.  
\end{table} 
Table 3: Mix proportions of concrete. Figure 2: Longitudinal section views of test specimens. (Unit: mm).