# Effect Mechanism of Connection Joints in Fabricated Station Structures
## 5 Damage Assessment Method of the Joint  
The damage analysis of fabricated structures can reflect the performance directly and comprehensively and is related to the structure's performance index of deformation, stiffness, and energy. The actual earthquake disaster showed that the failure of concrete structures starts at the material level and then accumulates to cause damage to the parts and the structure, eventually leading to the breakdown of the whole structure [56]. Figure 14 shows the concrete compression damage contour graph at the contact surface of the joint surrounded by the green dashed line.  
The joint compression damage index (\(d_{\text{joint,max}}\)) is the maximum value of the contact surface's compression damage index between block S and block M. \(d_{\text{joint, S}}/d_{\text{joint, M}}\) is defined as the compression damage index of the contact surface between block S and block M, as shown in Equation (8):  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{3}{*}{
\begin{tabular}{c} **Peak** \\ **Acceleration** \\ \end{tabular} } & \multirow{3}{*}{**CC**} & \multirow{3}{*}{**QD**} & \multirow{3}{*}{**SZ**} & \multicolumn{3}{c}{**Impact Rate (\%)**} \\ \cline{4-7}  & & & & & **QD** & **SZ** & **SZ** \\ \cline{4-7}  & & & & **Compared** & **with CC** & **with QD** & **with CC** \\ \hline
0.1 g & 2.90 & 2.77 & 2.92 & \(-4.38\%\) & 5.23\% & 0.69\% \\
0.2 g & 3.04 & 3.13 & 3.13 & 2.73\% & \(-0.03\%\) & 2.96\% \\
0.3 g & 3.78 & 3.87 & 3.87 & 2.46\% & \(-0.13\%\) & 2.38\% \\ \hline \hline \end{tabular}
\end{table}
Table 16: Maximum bending moments (\(\times 10^{3}\) kN\(\cdot\)m).  
Figure 14: The compression damage contour graphs of the contact surface.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{3}{*}{
\begin{tabular}{c} **Peak** \\ **Acceleration** \\ \end{tabular} } & \multirow{3}{*}{**CC**} & \multirow{3}{*}{**QD**} & \multirow{3}{*}{**SZ**} & \multicolumn{3}{c}{**Impact Rate (\%)**} \\ \cline{4-7}  & & & & **QD** & **SZ** & **SZ** \\ \cline{4-7}  & & & & **with CC** & **with QD** & **with CC** \\ \hline
0.1 g & 3.90 & 3.90 & 3.85 & 0.05\% & \(-1.23\%\) & \(-1.28\%\) \\
0.2 g & 5.28 & 5.13 & 5.15 & \(-2.80\%\) & 0.39\% & \(-2.46\%\) \\
0.3 g & 5.45 & 5.54 & 5.47 & 1.58\% & \(-1.21\%\) & 0.37\% \\ \hline \hline \end{tabular}
\end{table}
Table 15: Maximum shear forces (\(\times 10^{3}\) kN).  
\[d_{\text{joint,max}}=\max\{d_{\text{joint, S, }}d_{\text{joint, M}}\}\] \[d_{\text{joint}}=\sum\limits_{i}\frac{A_{i}}{A}d_{c,i} \tag{8}\]  
where \(d_{c,i}\) is the compression damage factor of finite element node \(i\), \(A_{i}\) is the area of node \(i\) within the contact surface, and \(A\) is the total area of the contact surface. Compressive damage represents the irreversible compressive damage of concrete (0 represents no damage and 1 represents complete damage). According to the CDP model, the joint residual strength index (\(R_{\text{joint}}\)) is shown by Equation (9):  
\[R_{\text{joint}}=\left\{\begin{array}{cc}1&d_{\text{joint}}\leq d_{c}\\ 1-d_{\text{joint}}&d_{\text{joint}}>d_{c}\end{array}\right. \tag{9}\]  
where \(d_{c}\) is the compression damage factor at the limited compression yield stress, which was taken as 0.173. The joint completely failed to have load-bearing capacity when the concrete residual strength index reached 90%.