Applying Weigh-in-motion traffic data to reliability based assessment of bridge structures

The knowledge of the process of the deterioration of structural resistance is crucial for existing bridge assessment. However, precisely modeling the process of loading also affects the evaluation. Indeed traffic loading is one of the main loads that a bridge is subjected to in its service time. This paper investigates the role of traffic loading on the time-dependent reliability of a given bridge. Emphasis is placed on updating traffic load effect models with consideration of traffic evolution due to traffic growth, change of traffic composition and modification of the weight limit regulation. Moreover, loss of resistance due to chloride induced corrosion is taken in account. Finally, the annual reliability is evaluated to quantify the influence of traffic evolution on the reliability of a reinforced concrete bridge. caused by the passage of the traffic loads can be easily calculated by combination with influence lines or surfaces of the load effect of interest. Then the lifetime maximum distribution of the effects can be studied using extreme value analysis. The paper is organized as follows: Section 2 introduces the resistance loss model for reinforced concrete beam. A detailed traffic load effect modeling method with consideration of traffic evolution is presented in Section 3. Section 4 illustrates the influence of traffic evolution on bridges with an example. Conclusion is drawn in Section 5. 2 CAPACITY LOSS DUE TO CHLORIDE INDUCED CORROSION During service time, the resistance of the structure of the bridge may degrade due to many factors, like environmental aggression, cracking, fatigue damage etc. For reinforced concrete bridge structures, the resistance degradations are mainly due to reinforcing steel corrosion and concrete cracking. Chloride concentration and carbonation are two main factors inducing reinforcing steel corrosion. In this article we deal only with the degradation induced by chloride aggression as major failure mode of RC bridges for which steel reinforcement corrosion is due to deicing salt (Weyers et al. 1994). The degradation of resistance is commonly assessed through the reduction of the tensile reinforcement area, As, and the area in age, t, is estimated to be: