# Delaying the Occurrence of Bar Buckling in RC Columns Confined with SRG Jacketing
## 3 Test Results and Discussion
### Response under Monotonic Axial Load
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Name**} & \multicolumn{2}{c}{\(\rm{f_{cc}}\) (MPa)} & \multicolumn{2}{c}{\(\rm{\epsilon_{cc}}\)} & \multicolumn{2}{c}{\(\rm{\epsilon_{lat,cc}}\)} & \multicolumn{2}{c}{\(\rm{\epsilon_{cou}}\)} & \multicolumn{2}{c}{\(\rm{\mathbf{f_{cc}/f_{o}}}\) *} & \(\rm{\epsilon_{cov}/\epsilon_{y}}\) * \\ \cline{2-11}  & **Value** & **Mean** & **Value** & **Mean** & **Value** & **Mean** & **Value** & **Mean** & **Mean** & **Mean** & **Mean** \\ \hline
**(1)** & \multicolumn{2}{c}{**(2)**} & \multicolumn{2}{c}{**(3)**} & \multicolumn{2}{c}{**(4)**} & \multicolumn{2}{c}{**(5)**} & \multicolumn{2}{c}{**(6)**} & \multicolumn{2}{c}{**(7)**} & \multicolumn{2}{c}{**(8)**} \\ \hline A-1 st  & 31.9 & \multirow{2}{*}{0.0070} & \multirow{2}{*}{0.0065} & \multirow{2}{*}{0.009} & \multirow{2}{*}{0.0098} & \multirow{2}{*}{1.08} & \multirow{2}{*}{2.60} & \multirow{2}{*}{3.93} \\ \cline{2-2} \cline{4-11} L1A-2 nd & 30.6 & & 0.0060 & & & & & & & \\ \hline L2A-1 st  & 36.3 & \multirow{2}{*}{38.3} & 0.0160 & \multirow{2}{*}{0.0155} & \multirow{2}{*}{0.040} & \multirow{2}{*}{0.045} & \multirow{2}{*}{0.0180} & \multirow{2}{*}{1.32} & \multirow{2}{*}{6.20} & \multirow{2}{*}{7.37} \\ \cline{2-2} \cline{4-11} H2A-2 nd & 40.3 & & 0.0150 & & & & & & & \\ \hline B-1 st  & 34.7 & \multirow{2}{*}{34.0} & \multirow{2}{*}{0.0060} & \multirow{2}{*}{0.0060} & \multirow{2}{*}{0.012} & \multirow{2}{*}{0.0109} & \multirow{2}{*}{0.0105} & \multirow{2}{*}{1.17} & \multirow{2}{*}{2.4} & \multirow{2}{*}{4.19} \\ \cline{2-2} \cline{4-11} L1B-2 nd & 33.4 & & 0.0060 & & & & & & & \\ \hline L2B-1 st  & 41.3 & \multirow{2}{*}{0.0130} & \multirow{2}{*}{0.0165} & \multirow{2}{*}{1.42} & \multirow{2}{*}{5.80} & \multirow{2}{*}{6.60} \\ \cline{2-2} \cline{4-11} L2B-2 nd &An interesting observation is that the axial stress-strain response for most of the SRG-jacketed columns (Figure 7) is characterized by a horizontal plateau at strength, although the steel textile has an elastic behaviour up to rupture (like to FRP fabrics). This may be attributed to the elastoplastic bond-slip law of the SRG, which presents a wide plateau at bond strength between slip values 0.1-0.5 mm, and the upper limit further increases up to 1 mm with bonded length over 200 mm [25, 26]. The corresponding bond-slip law of the FRP usually has a parabolic shape that terminates at slip of 0.2-0.3 mm [27]. The variation in bond response between the SRG and FRP jacketing systems potentially explains why the SRG jacket enables plastic response under axial compression, whereas the FRP jacket results in a hardening branch following elastic response [12, 28]. The test data are analysed for two limit states of response as defined in Figure 7d and are summarized in Table 2. The first state corresponds to the strength beyond which a descending branch initiates (columns (2-3) in Table 2); point (\(\ell_{\text{co}}\), \(\ell_{\text{co}}\)) for the control specimens and point (\(\ell_{\text{cc}}\), \(\ell_{\text{cc}}\)) for the confined ones in Figure 7d. The lateral strain \(\varepsilon_{\text{lat,cc}}\) is also defined at this level (column (4) in Table 2). The second state corresponds to the ultimate state which is defined at 15% drop of strength (column (5) in Table 2); points (\(\ell_{\text{cu}}\), \(\varepsilon_{\text{cu}}\)) and (\(\ell_{\text{ccu}}\), \(\varepsilon_{\text{ccu}}\)) for the control and SRG confined columns, respectively. The proximity of the two states denotes how abruptly the strength degradation occurs. Column (6) denotes the increased strength of the SRG-jacketed columns as compared with the concrete strength  
Figure 7: Axial stress–strain curves of the tested SRG jacketed columns; (**a**) 1 layer–4 cords/in; (**b**) 2 layers–4 cords/in; (**c**) 2 layers–12 cords/in. (**d**) Nomenclature for the axial stress–strain milestone points. (f\({}_{0}\) = 29 MPa).