## 4 Seismic Response CFST Structure with BRBs under Earthquake Sequences
### Nonlinear Response Analysis under Sequence-Type Ground Motion
In the first situation, \(\delta\) is relatively small, and the amplitude of the foreshock is relatively small, while the magnitude of the mainshock is relatively large in the earthquake sequence. After the foreshock, the structure is still in an elastic state, but, after the mainshock, the structure enters a nonlinear state, which results in structural plastic damage. In the second situation, \(\delta\) is relatively large, and the peak amplitudes of both the foreshock and the mainshock in the earthquake sequence are large. As a result, the structure has already undergone moderate or severe damage during the foreshock, which exhibits notable plastic characteristics and stiffness degradation. When subjected to the mainshock with a higher intensity, the structural cumulative damage increases significantly, and the stiffness further decreases. At this time, the damaged structure experiences a strong aftershock, and the risk of collapse to the structure greatly increases. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Input** \\ **Motions** \\ \end{tabular} } & \multirow{2}{*}{**PGA (g)**} & \multicolumn{6}{c}{**ISDR (10\({}^{-3}\))**} \\ \cline{3-10}  & & & **Earthquake** & **Difference** & **Earthquake** & **Difference** & **Earthquake** & **Difference** \\  & & **Only** & **(8 = 0.4)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** \\ \hline M-AGW & 0.032 & 0.42 & 0.52 & 21.92 & 0.58 & 36.44 & 0.62 & 45.62 \\ A-CAT & 0.042 & 0.60 & 0.72 & 20.02 & 0.77 & 27.58 & 0.79 & 31.60 \\ A-STP & 0.049 & 0.79 & 0.86 & 9.01 & 0.87 & 10.41 & 1.04 & 31.30 \\ HO6 & 0.060 & 0.37 & 0.40 & 7.62 & 0.44 & 18.10 & 0.47 & 24.97 \\ A-CTS & 0.062 & 0.60 & 0.69 & 15.78 & 0.70 & 17.71 & 0.85 & 41.82 \\ A-HAR & 0.070 & 1.54 & 1.60 & 3.81 & 1.70 & 10.03 & 1.88 & 22.07 \\ H-CO8 & 0.100 & 2.30 & 2.46 & 6.89 & 2.95 & 28.33 & 3.24 & 41.06 \\ H-CCA & 0.115 & 1.23 & 1.40 & 13.55 & 1.66 & 34.46 & 1.76 & 42.45 \\ H-CAL & 0.128 & 0.71 & 0.84 & 17.48 & 0.90 & 25.50 & 0.99 & 38.24 \\ H-CMP & 0.144 & 2.51 & 2.62 & 4.29 & 3.02 & 20.36 & 3.55 & 41.12 \\ BRA & 0.160 & 0.95 & 0.98 & 3.82 & 1.12 & 18.38 & 1.23 & 30.01 \\ M-GMR & 0.184 & 0.68 & 0.73 & 6.23 & 0.78 & 13.84 & 0.80 & 17.08 \\ M-G03 & 0.194 & 0.85 & 0.92 & 7.33 & 0.94 & 9.45 & 0.99 & 15.58 \\ M-G02 & 0.200 & 1.20 & 1.48 & 23.13 & 1.59 & 32.30 & 1.68 & 39.64 \\ A-DWN & 0.215 & 3.24 & 3.62 & 11.76 & 4.23 & 30.42 & 4.27 & 31.65 \\ FLE & 0.237 & 2.20 & 3.11 & 41.26 & 3.20 & 45.45 & 3.48 & 58.03 \\ C08 & 0.259 & 3.02 & 3.11 & 3.05 & 3.40 & 12.58 & 3.66 & 21.07 \\ H-CHI & 0.269 & 4.01 & 5.19 & 29.29 & 5.99 & 49.31 & 6.06 & 50.94 \\ A-BIR & 0.299 & 1.92 & 2.26 & 17.44 & 2.34 & 21.67 & 2.79 & 45.22 \\ I-ELC & 0.309 & 6.90 & 8.70 & 26.09 & 9.50 & 37.69 & 10.11 & 46.55 \\ A-CAS & 0.322 & 3.36 & 3.71 & 10.42 & 4.13 & 22.92 & 4.31 & 28.27 \\ H-DLT & 0.349 & 0.93 & 1.40 & 51.47 & 1.55 & 67.01 & 1.63 & 76.23 \\ HOL & 0.358 & 6.74 & 6.97 & 3.41 & 7.38 & 9.50 & 8.18 & 21.31 \\ CAP & 0.395 & 3.87 & 4.10 & 5.94 & 4.27 & 10.34 & 4.59 & 18.64 \\ G04 & 0.413 & 3.99 & 4.75 & 18.95 & 5.64 & 41.35 & 6.55 & 64.16 \\ G03 & 0.547 & 21.23 & 22.83 & 7.54 & 26.75 & 25.98 & 30.88 & 45.46 \\ SCS & 0.612 & 74.95 & 84.61 & 12.89 & 106.15 & 41.63 & 109.75 & 46.43 \\ H-BCR & 0.780 & 27.60 & 29.02 & 5.14 & 30.24 & 9.57 & 34.99 & 26.79 \\ RKS & 0.834 & 111.24 & 121.52 & 9.24 & 134.90 & 21.27 & 144.43 & 29.84 \\ SPV & 0.939 & 34.97 & 36.02 & 2.99 & 37.53 & 7.32 & 41.76 & 19.43 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Maximum ISDR under mainshock and earthquake sequence.