## 3 Test Results and Discussion
### Behavior and Failure Mode  
Two types of the behaviors were observed from the specimens. Therefore, failure of the specimens can be classified into two failure types: flexural failure and punching shear failure. Two specimens  
Figure 4: Test setup. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline \multirow{2}{*}{**Specimen**} & **Ultimate Strength** & **Strength Increase \({}^{*}\) & **Deflection \({}^{**}\)** & **Failure Mode** & **Initial Stiffness (kN/mm)** \\  & **(kN)** & **(\%)** & **(mm)** & **Failure Mode** & **Initial Stiffness (kN/mm)** \\ \hline CSR1-C1-F0 & 113.7 & - & 15.99 & Flexural & 29.9 \\ CSR1-C1-F1 & 172.1 & 51.4 & 6.42 & Punching shear & 45.3 \\ CSR1-C1-F2 & 186.2 & 63.8 & 5.86 & Punching shear & 51.7 \\ CSR1-C2-F0 & 136.8 & - & 20.93 & Flexural & 43.4 \\ CSR1-C2-F1 & 209.1 & 52.9 & 7.66 & Punching shear & 49.8 \\ CSR1-C2-F2 & 229.1 & 67.5 & 6.96 & Punching shear & 49.3 \\ CSR2-C1-F0 & 145.9 & - & 7.52 & Punching shear & 37.1 \\ CSR2-C1-F1 & 170.6 & 16.9 & 6.32 & Punching shear & 38.9 \\ CSR2-C1-F2 & 196.8 & 34.9 & 6.48 & Punching shear & 39.0 \\ CSR2-C2-F0 & 176.1 & - & 9.11 & Punching shear & 40.3 \\ CSR2-C2-F1 & 225.0 & 27.8 & 7.54 & Punching shear & 51.1 \\ CSR2-C2-F2 & 248.2 & 40.9 & 6.57 & Punching shear & 51.2 \\ \hline \hline \end{tabular}  
* Compared to the control specimen (-F0), without CFRP laminates). \({}^{**}\) Measured at the center of the slab when the specimen reached its ultimate strength.  
\end{table} 
Table 3: Test results. CSR1-C1-F0 and CSR1-C2-F0 (without laminates) developed flexural cracking on the tension side of the slab, along the diagonal direction of the slab and extended to the corners of the slab. These two specimens finally failed in flexure and showed a typical yield line failure mechanism on the tension side of the slab, as shown in Figure 5a. Failure of the remaining specimens was clarified as the punching shear failure because the stub column suddenly punched through the slab at failure, accompanied by much smaller deflection of the slabs compared to that of the specimens failed in flexural. The load-carrying capacities dropped in a second when punching shear failure occurred. For those CFRP-strengthened specimens, there was no damage or debonding of the CFRP laminates at their ultimate loads, even though the laminates did not have a special anchor. After the slabs reached their ultimate loads, the CFRP laminates were gradually debonded starting from the vicinity of the crack surface when the stub column was pushed further. After the test, the laminates were peeled to examine the crack surface that was near a circle with approximate diameter of 360 to 600 mm, as shown in Figure 6. Typical cracking patterns of the slabs failed in punching are shown in Figure 5b,c. For the CFRP-strengthened specimens, there was no cracking within the truncated cone due to the strengthening of the laminates (Figure 5c), while the specimens CSR2-C1-F0 and CSR2-C2-F0 (without laminates) displayed more cracking within the truncated cone (Figure 5b). Two specimens failed in a ductile manner by forming yield lines on the slab, while the remaining specimens exhibited a failure mode of punching. The formation of flexural or punching failure was addressed in the literature [14; 15]. A lightly reinforced slab-column connection resulted in a ductile failure, but using a higher amount of the flexural reinforcement on the connection leads to a punching shear failure. In this test, the change of the failure mode from a ductile manner (specimens CSR1-C1-F0 and CSR1-C2-F0) to a brittle mode of punching shear failure (CFRP-strengthened specimens) was attributed primarily to the strengthening contributed from the CFRP laminates. The CFRP laminates  
Figure 5: Typical cracking patterns on the tension surface of the slab: **(a)** Flexural failure; **(b)** Punching shear failure of slabs without CFRP laminates; **(c)** Punching shear failure of slabs with CFRP laminates.