ABSTRACT
The passage of a vehicle over a bridge gives rise to cyclical and variable stresses, generally below the yield strength of the material used in the structure. The vehicles that travel on Brazilian highways have changed a lot in the last decades. It has been noticed an increase in the load traffic and in the number of trucks in the highways. In addition, the majority of Brazilian bridges is reaching their service lives (50 years). Thereby, these bridges have already been submitted to the passage of millions of vehicles, i.e., millions of stress cycles.
Given all that, it is clear that there is a need to assess the remaining fatigue life of these structures in order to ensure safety in their use. One possibility to assess the service life of structures is to apply bridge weigh-in-motion (BWIM) techniques together with S-N curves given by international standards, and a linear accumulation damage rule according to the Palmgren-Miner procedure. BWIM systems are capable of acquiring the actual traffic load and also the bridge response in terms of actual strains.
This proposed method was applied to a short reinforced concrete bridge, monitored by a BWIM system for 42 days. S-N curves given by the Eurocode and the Brazilian standard were used. The stress cycles were counted with the rainflow method. The service life, in years, was estimated considering damage due to each stress cycle together with the average daily number of cycles, as given by Equation (1). () Y = 1 365 × A D C × D C https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/eq162.tif"/>
where Y is the service life to fatigue in years; ADC is the average number of cycles per day; DC is the damage due to one cycle.
The estimation of fatigue life for each girder and bridge are shown in Figure 1 for different levels of variable amplitude fatigue limite (VAFL) considering the S-N curve given in the Eurocode 2. It is concluded that the consideration of the VAFL value between 25 to 33% of the constant amplitude fatigue limit (CAFL) would better describe the actual state of conservation of the evaluated bridge. However, the proposed method could be further improved if bridge degradation and traffic expectancy reliability models are taken into account. Expected service life with S-N curve given by Eurocode. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig275_1.tif"/>
