## 3 Methodology
### Technical Condition Assessment
#### 3.1.3 Calculation of Progressive Assessment
\begin{split}\text{MCCI}_{i}=\overline{\text{MMCI}}_{i}-(100- \text{MMCI}_{i,\;\text{min}})/t\\ \text{ACCI}_{i}=\overline{\text{AMCI}}_{i}-(100-\text{AMCI}_{i,\; \text{min}})/t\\ \text{MCCI}_{i}(\text{ACCI}_{i})=0\;,\;\text{when MCCI}_{i}(\text{ACCI}_{i})<0 \end{split} \] (2) where MCCI and ACCI are the condition indices of components, which belong to the main structure and accessory structure, respectively; \(i\) denotes component \(i\); \(t\), as is illustrated in Table 8, is the correction coefficient, which is a variable with the quantity of members and introduced to neutralize the adverse effect of individual members on overall component technical condition assessment. 3. Technical condition assessment of BECI main structure and accessory structure The technical condition assessment of BECI main structure and accessory structure is calculated as follows: \[\text{MSCI}(\text{ASCI})=\sum\limits_{i=1}^{c}\text{MCCI}_{i}(\text{ACCI}_{i} )\times\text{W}_{i}\] (3) where here MSCI and ASCI are the condition indices of main structure and accessory structure; \(i\) denotes component \(i\); \(c\) represents the quantity of components; as is shown in Table 9, \(W_{i}\) is the calculation weight of each component, which is established via an analytic hierarchy process method under the guidance of the transportation industry standard of the People's Republic of China [35; 36]. 4. Technical condition assessment of overall BECI The technical condition assessment of overall BECI is calculated as follows: \[\text{S}_{\text{I}}=\text{MSCI}\times\text{W}_{MS}+\text{ASCI}\times\text{W }_{AS}\] (4) where \(\text{S}_{\text{I}}\) denotes the summative condition index of overall BECI; \(W_{MS}\) and \(W_{AS}\) are the calculation weights of the main structure and accessory structure, respectively, which are valued according to Table 10.
5. Technical condition scale classification of BECI In accordance with the computation results of \(\text{S}_{\text{I}}\), the technical condition scales \(\text{S}_{\text{S}}\) of BECI are classified and corresponding maintenance suggestions are proposed, which is exhibited in Table 11.
6. Inspection control index of BECI In particular, the technical condition scale of BECI will be classified as 4 without following up subsequent assessment process if the results of on-site inspection satisfy the inspection control indices, which implies that a BECI replacement is necessary to be developed immediately. The inspection control indices of BECI are proposed as follows:  
* More than 2 fractures occur in side beam or intermediate beam;
* The damaged area of comb plate exceeds 30% and more than 3 defective units occur;
* The damaged area of elastic expansion body exceeds 30%. Compared with traditional inspection, this approach allows an exact number to be output when on-site inspectors find that the BECI is between two scales and it is difficult to completely make judgment, which proves the most significant improvement. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**The Highest Scale That Can Be Achieved by** & \multicolumn{5}{c}{**Scale of Inspection Index**} \\ \cline{2-6}
**Inspection Index** & **1** & **2** & **3** & **4** \\ \hline
4 & 0 & 25 & 50 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Deduct point of inspection index.