ABSTRACT
High-cycle fatigue behaviour of reinforced concrete bridges depends on characteristics of the concrete, the steel reinforcement and the interaction between both. Fatigue safety can be studied in a more realistic way using field strain measurements. Analytical methods in most cases are not enough for an exact evaluation of distributed loading along the different structural members due to the assumptions adopted in the idealized models (Zhou 2006). In the case of reinforced concrete bridges, the combined action between concrete and steel reinforcement and the geometry of the elements cannot be properly represented. In addition to this, there are also uncertainties in the live load characterization due to variation of vehicle weight and random traffic.
In this paper, the fatigue-induced damage of a reinforced concrete highway bridge has been determined using the measured load spectrum obtained through long-term monitoring. The fatigue assessment of concrete and steel reinforcement is evaluated based on traditional methods.
The reinforced concrete bridge over the Jaguari river, located at Extrema, in the Brazilian state of Minas Gerais, has been used for this paper as a case study. It is a curved, descending bridge, with a continuous slab cast integrally in two girders supported by six pairs of columns. It has 5 spans (20 m, 26 m, 30 m, 26 m and 20 m) and, in order to connect to the road, its extremities have abutments with a transition slab. Figure 1 provides a general view of the bridge. Overall profile of the Jaguari bridge. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig276_1.tif"/>
In 2013, a monitoring center was installed in this bridge with the goal of assessing its structural integrity and following its response throughout time.
The fatigue analysis has been conducted based on monitoring data, utilizing the S-N method and the Palmgren-Miner linear damage accumulation rule. The results have shown the infinite fatigue life for the Jaguari bridge. It must be noticed that the critical point of the structure is the 20 m span mid-section, at the welded longitudinal steel reinforcement of the girder. The welded connections significantly diminish the fatigue strength value for infinite life. The safety index at this point equals 1.07, showing the vulnerability of the system for the random nature of the loading – in other words, if a special cargo, above the permitted value for the bridge, passes through it, the fatigue damage process will be probably triggered up. Once triggered, the structure will be susceptible to fatigue failure.
