ABSTRACT
The majority of Brazilian bridges are made of reinforced concrete with spans smaller than 50 m. These bridges are reaching their design service life and, thus, have already been submitted to the passage of millions of vehicles. Furthermore, there have been an increase in the load traffic and in the number of trucks in the highways. Trucks with up to nine axles are usually seen nowadays. As a result, fatigue assessment is needed to ensure safety. Therefore, two reinforced concrete bridges were monitored with time intervals in order to assess their structural safety. The monitoring lasted 120 days in each structure. In this paper, the signals acquired at the midspan of the girders during the monitoring were used to assess the fatigue life of the bridges. Equivalent stresses were calculated from stress bin histograms for several variable amplitude fatigue limits (VAFL). In order to estimate the life cycle, it was used the tension-life (S-N) approach, using S-N curves from international standards. Moreover, it was considered a linear accumulation damage through the Palmgren-Miner rule with the counting of stress cycles given by the Rainflow method. Uncertainties about maximum stresses and bridge degradation were taken into account in a simplified way based on international standards recommendations. It is concluded that the consideration of VAFL value between 10% to 33% of the constant amplitude fatigue limit (CAFL) would better describe the actual state of conservation of the evaluated bridges. Also, it is not expected that fatigue will be the failure mechanism of these bridges.
