## 5 Conclusions  
A method was developed to evaluate the reliability of an in-service highway bridge based on resistance capacity degradation. The suggested method was applied to a PSC-I girder bridge to verify its effectiveness. The required performance and resistance capacity of the bridge reflecting various traffic characteristics were calculated. These were then used to analyze the bridge reliability. Various traffic characteristics were considered to analyze the required performance of the sample bridge. The decrease in the resistance capacity was analyzed according to the suggested deterioration model.  
The case with an AADT of 20,000 and heavy vehicle proportion of 25% was set as the normal traffic case. The case with an AADT of 10,000 and heavy vehicle proportion of 15% was set as the mild traffic case, and the case with an AADT of 40,000 and heavy vehicle proportion of 35% was set as the severe traffic case. The annual extreme load effect calculation from a previous study was used. The flexural moment generated by the dead load and live load primarily applied to bridges was analyzed to determine the required performance. The analysis results confirmed that the outer girder of the sample bridge required the highest level of performance.  
For the calculation of the resistance capacity, all variables considering the uncertainty of materials and sections were regarded as probabilistic variances. The statistical characteristics of the resistance capacity, materials, and sections were calculated by running a Monte Carlo simulation 100,000 times. The flexural resistance of the PSC-I girder was calculated to be 1.053 times larger than the nominal strength on average.  
The performance degradation of PSC-I girder bridges was calculated with the presented corrosion model. In order to examine the performance degradation in different corrosive environments, corrosive environments were classified as mild, normal, and severe. The results showed that the performance degradation was more rapid with wider initial cracks and in areas with higher surface chloride content. The reliability of the selected bridges was analyzed based on the limit state equation. The results showed that the annual reliability indices of PSC-I girder bridges with 75 years of service varied significantly depending on the corrosive environment, traffic conditions, and crack formation. These results indicate that reliability of a highway bridge based on the resistance capacity is quite sensitive to important parameters, including the traffic characteristics, corrosive environment, and crack damage. If such parameters are considered, the structural reliability level may decrease. Therefore, a maintenance plan for bridges should be rationally developed by considering the site environment.  
In this study, a method was developed for evaluating the performance and reliability degradation according to the time history by considering the effect of traffic characteristics and a corrosive environment, and the method was applied to an actual PSC-I girder bridge as an example. Further research is needed to apply the proposed method to maintenance based on repair and reinforcement, life cycle cost analysis, and reliability evaluation of other superstructure-type bridges.  
This study has been supported by a Creative Human Resources Center for Resilient Infrastructure grant funded by Yonsei University.  
[PERSON] proposed the topic of this study and designed the process; [PERSON] and [PERSON] performed the simulations; and [PERSON] performed the analysis and wrote the paper.  
The authors declare no conflict of interest.