## 4 Test Results and Discussions
### Quasi-Static Compression Tests
It is interesting to note that the hoop strain efficiency ratio (i.e., the value of the FRP hoop rupture strain, \(\varepsilon_{h,rup}\), over the FRP tensile strain, \(\varepsilon_{f}\)) is the smallest for the specimen with the thinnest FRP jacket and the hoop strain efficiency ratios of the BFRP-confined concrete specimens are much less than one, which is substantially different from those of the AFRP and CFRP-confined concrete specimens. This is probably because the BFRP jacket was more susceptible to the local failure of the high-strength concrete. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Specimen**} & \(f_{\alpha_{\alpha}}\) **or /\(f_{\alpha_{\alpha}}\) (MPa)** & \(f_{\alpha_{\alpha}}\) & \(\varepsilon_{\alpha_{\alpha}}\) **or /\(\varepsilon_{\alpha_{\alpha}}\) (MPa)** & \(\varepsilon_{\alpha_{\alpha}}\) & \(\varepsilon_{h,rup}\) & \(\varepsilon_{h,rup}\) & \(\varepsilon_{h,rup}\) \\  & **Test Average** & \(f_{\alpha_{\alpha}}\) & **Test Average** & & **Test Average** & & **Test Average** \\ \hline S-0-1 & 70.55 & & 0.0023 & & \(-\)0.0008 & & & 46.75 & \\ S-0-2 & 71.87 & **71.21** & **N.A.** & 0.0023 & 0.0023 & N.A. & \(-\)0.0007 & \(-\)0.0007 & N.A. & 44.31 & 44.70 \\ S-0-3 & 63.54 & & & 0.0024 & & \(-\)0.0007 & & & 43.03 & \\ S-Bi-1 & 75.41 & & & 0.0030 & & \(-\)0.0013 & & & 41.33 & \\ S-Bi-2 & 74.01 & 75.96 & 1.07 & 0.0031 & 0.0030 & 1.30 & \(-\)0.0028 & \(-\)0.0021 & 0.13 & 40.25 & 41.48 \\ S-Bi-3 & 78.47 & & & 0.0030 & & \(-\)0.0022 & & & 42.86 & \\ S-Bi-2 & 80.25 & & & 0.0031 & & \(-\)0.0028 & & & 39.69 & \\ S-Bi-2 & 80.38 & 80.32 & 1.13 & 0.0039 & 0.0035 & 1.53 & \(-\)0.0027 & \(-\)0.0028 & 0.18 & 43.06 & 41.38 \\ S-Bi-3 & 68.41 & & & 0.0030 & & \(-\)0.0035 & & & 49.36 & \\ S-Bi-1 & 93.12 & & & 0.0079 & & \(-\)0.0132 & & & 41.93 & \\ S-Bi-2 & 90.45 & 93.25 & 1.31 & 0.0070 & 0.0075 & 3.26 & \(-\)0.0126 & \(-\)0.0133 & 0.83 & 39.33 & 41.08 \\ S-Bi-3 & 96.18 & & & 0.0077 & & \(-\)0.0140 & & & 41.97 & \\ S-Bi-1 & 77.32 & & & 0.0038 & & \(-\)0.0052 & & & 44.40 & \\ S-Bi-2 & 97.96 & 94.01 & 1.32 & 0.0115 & 0.0109 & 4.73 & \(-\)0.0163 & \(-\)0.0150 & 1.14 & 41.75 & 40.55 \\ S-Bi-3 & 90.06 & & & 0.0102 & & \(-\)0.0136 & & & 39.95 & \\ S-Bi-2 & 115.41 & & & 0.0138 & & \(-\)0.0131 & & & 42.86 & \\ S-Bi-2 & 129.04 & 127.66 & 1.79 & 0.0171 & 0.0170 & 7.39 & \(-\)0.0193 & \(-\)0.0192 & 1.45 & 38.14 & 39.45 \\ S-Bi-3 & 128.41 & & & 0.0169 & & & \(-\)0.0190 & & & 37.34 & \\ S-Bi-3 & 170.96 & & & 0.0192 & & \(-\)0.0194 & & & 47.28 & \\ S-Bi-3 & 162.42 & 164.67 & 2.31 & 0.0176 & 0.0192 & 8.35 & \(-\)0.0179 & \(-\)0.0186 & 1.41 & 36.24 & 39.69 \\ S-Bi-3 & 160.64 & & & 0.0209 & & & \(-\)0.0134 & & & 35.56 & \\ S-Bi-3 & 105.39 & & & 0.0114 & & & \(-\)0.0130 & & & 39.74 & \\ S-Bi-3 & 99.26 & 105.83 & 1.49 & 0.0114 & 0.0115 & 5.00 & \(-\)0.0126 & \(-\)0.0129 & 0.77 & 37.78 & 39.04 \\ S-Bi-3 & 112.84 & & & 0.0116 & & & \(-\)0.0132 & & & 39.60 & \\ S-Bi-2 & 150.31 & & & 0.0198 & & & \(-\)0.0161 & & & 35.92 & \\ S-Bi-2 & 126.64 & 149.43 & 2.10 & 0.0152 & 0.0191 & 8.30 & \(-\)0.0138 & \(-\)0.0160 & 0.96 & 38.71 & 38.87 \\ S-Bi-2 & 148.54 & & & 0.0183 & & & \(-\)0.0158 & & & 41.97 & \\ S-Bi-2 & 129.36 & 197.71 & 2.78 & 0.0183 & 0.0212 & 9.22 & \(-\)0.0150 & & & 42.22 & 38.68 \\ S-Bi-3 & 203.06 & & & 0.0241 & & & \(-\)0.0156 & & & 42.05 & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Test results of specimens under quasi-static compression loadings. Figure 7: Stress–strain curves of the CFRP-confined concrete specimens under quasi-static compression. **(a)** One-layer CFRP-confined specimens; **(b)** Two-layer CFRP-confined specimens; **(c)** Three-layer CFRP-confined specimens; and **(d)** CFRP-confined and unconfined specimens.