## 5 Conclusions  
An intelligent approach for structural system reliability evaluation based on DBNs was presented. Mathematical models for system reliability evaluation of cable-stayed bridges were derived takinginto consideration the structural nonlinearity and high-order statically indeterminate characteristics. The theoretical basis for utilizing DBNs to approximate the structural load was introduced. A computational framework was presented to illustrate the procedures followed to evaluate the bridge  
Figure 16: Influence of the cable strength degradation on the system reliability of the suspension bridge.  
Figure 15: Series-parallel relationship of the three-level.  
system reliability via DBNs. The feasibility of the computational framework was demonstrated in a case study using a prototype suspension bridge. The conclusions are summarized as follows:  
1. DBN provides an accurate approximation of the load effect of a cable-supported bridge, taking into consideration the structural nonlinearity in the behavior of the system. Thus, DBN can be utilized as a meta-model for a large number of simulations as a result of reliability analysis.
2. The suspender was found to have a relatively low reliability index, while that of the main cable was the highest. Therefore, the first component that was mostly likely to fail should be the suspender. In addition, the degradation of suspenders due to fatigue-corrosion damage was found to have a significant effect on the system reliability of the cable-supported bridge.
3. The system reliability index of the prototype suspension bridge is 9.63 considering the three-level system fault tree. Accounting for fatigue damage and fatigue-corrosion damage, the system reliability index decrease to 7.22 and 4.41, respectively.
4. According to the design standard for the structural reliability of highway bridges in China, a bridge controlled by brittle failure should have a reliability index greater than 5.2. Cable replacement should take place after 26 years of service time accounting for the fatigue-corrosion damage of suspenders.  
Since fatigue-corrosion damage is the main factor leading to bridge safety degradation, further studies should focus on the cable degradation behavior and its effect on the failure sequence of bridges. In addition, more site-specific inspection data of the cables are needed to formulate the cable replacement scheme. Wind loads, seismic loads, and temperature loads should be taken into consideration in the reliability model, since these parameters are more critical for flexible bridges. Finally, structural health monitoring data can be employed to update the reliability model.  
Conceptualization, N.L.; Methodology, Y.L.; Data curation, X.X.; Writing--original draft preparation, N.L.; Writing--review and editing, N.L.; Supervision, M.N.; Project administration, N.L.; Funding acquisition, N.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by [National Science Foundation of China] grant number [51908068], [National Science Foundation of Hunan Province] grant Numbers [2020 JJ5140 and 2020 JJ5589], [Open Fund of Key Laboratory of Bridge Engineering Safety Control in the Department of Education in Changsha University of Science and Technology] grant numbers [19 KF03 and 19K0B2], and [Innovation Platform Open Fund Project of Hunan Education Department] grant number [19K002]. The APC was funded by Changsha University of Science and Technology.  
The authors declare no conflict of interest.