# Seismic Performance of LRS-FRP-Concrete-Steel Tubular Double Coupling Beam
## 3 Results and Discussion
### Hysteretic Curve
After measuring the lateral deformation, go back to zero. The bearing capacity contributed by concrete changes from compression to shear. The concrete damage and the slippage between steel bar and concrete resulted in the pinching phenomenon. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No. **} & \multirow{2}{*}{ \begin{tabular}{c} **V\({}_{y}\) 1** \\ **(kN)** \\ \end{tabular}  } & \(\Delta_{y}\)2 [FOOTNOTE:2]Footnote 2: \(V_{y}\) and \(V_{p}\) are the yield strength and peak strength of the specimens, respectively; \(V_{x}\) is the ultimate strength based on the 85% of peak strength of the specimens; \(V_{y,tip}\) is the ultimate strength based on the rupture of FRP; \(\Delta_{y}\), \(\Delta_{y}\), \(\Delta_{u}\), and \(\Delta_{u,tip}\) are the deformation corresponding to \(V_{y}\), \(V_{p}\), \(V_{u}\), and \(V_{u,tip}\), respectively; 3 [FOOTNOTE:3]Footnote 3: \(V_{y}\) and \(V_{p}\) are the yield strength and peak strength of the specimens, respectively; \(V_{u}\) is the ultimate strength based on the 85% of peak strength of the specimens; \(V_{u,tip}\) is the ultimate strength based on the rupture of FRP; \(\Delta_{y}\), \(\Delta_{y}\), \(\Delta_{u}\), and \(\Delta_{u,tip}\) are the deformation corresponding to \(V_{y}\), \(V_{p}\), \(V_{u}\), and \(V_{u,tip}\), respectively; 3 [FOOTNOTE:3]Footnote 3: \(V_{y}\) and \(V_{p}\) are the yield strength and peak strength of the specimens, respectively; \(V_{u}\) is the ultimate strength based on the 85% of peak strength of the specimens; \(V_{u,tip}\Relatively, the hysteretic curves of the specimens DST-DCB-89, DST-DCB-76, and DST-DCB-89P illustrated in Figure 8 are similar to each other except for some details. Compared to the specimen, LRS-DCB, as shown in Figure 8, Figure 10, and Table 4, the yield stress, peak stress, ultimate stress, and corresponding deformation of DST-DCB-89, DST-DCB-76, and DST-DCB-89P improved significantly: (1) the yielding stress of these three specimens improved by 41%, 37%, and 27%, respectively. Meanwhile, the corresponding lateral deformation improved by 20%, 31%, and 20%, respectively; (2) the peak stress of these three specimens improved by 39%, 38%, and 27%, respectively. The corresponding lateral deformation improved by 8%, 23%, and 23%, respectively; (3) the ultimate stress was based on 85% of the peak strength of these three specimens improved by 18%, 17%, and 8%, respectively. The corresponding lateral deformation decreased by 71%, 115%, and 121%, respectively. Moreover, the ductility coefficient of specimens LRS-DCB, DST-DCB-89, DST-DCB-76, and DST-DCB-89P improved by 292%, 42%, 65%, and 82%, respectively, based on the 85% peak strength compared to the control specimen. Compared to the peak stress and ultimate stress of those DST-DCB specimens, we determined that the the bearing capacity enhancement was mainly caused by the embedded steel tube. As the lateral deformation and cycle times increase, the bearing capacity also increases until the inner steel tube buckling due to insufficient support inside. Compared to the LRS-DCB specimen, the force of those three specimens with DST dropped rapidly at first and then stabilized. However, as shown in Figure 10 and Table 4, the strengths of the four specimens are similar to each other when the wrapped PET-FRP sheet ruptures, indicating that the wrapped PET-FRP jacket's constraint effect could effectively prevent further reduction of the bearing capacity. Hence, the enhanced strength of those DST-DCB specimens could act as energy storage for the specimen design. As shown in Table 4, the deformation of DST-DCB-89, DST-DCB-76, and DST-DCB-89P corresponding to the  
Figure 10: Analysis of the skeleton curves: (**a**) RC-DCB vs. LRS-DCB; (**b**) LRS-DCB vs. DST-DCB-89 vs. DST-DCB-76; (**c**) DST-DCB-89 vs. DST-DCB-76; (**d**) DST-DCB-89 vs. DST-DCB-89P. PET-FRP rupture improved by 300%, 253%, and 300%, respectively, compared to the control specimen. These results are similar to those recorded for the LRS-DCB specimen.