Development of truck weight limits for concrete bridges using reliability theory

Resumo

The increase in gross weight limits allowed by Brazilian legislation and the proliferation of new truck configurations in national highways motivate concern regarding the structural safety of bridges when submitted to real traffic. This paper verifies the performance of the bridges under DER-SP jurisdiction using the reliability index β and obtains truck weight limits in order to guarantee its structural integrity. The superstructures of reinforced and prestressed concrete bridges, classes 36 and 45, are considered. The ultimate limit state is verified in cross sections submitted to critical positive and negative bending moments. In case of prestressed bridges, the tension limit state in concrete is added. The real traffic is represented by a live load model based on weighting data collected from stations located at highways of the state of Sao Paulo and the statistical parameters of resistance are determined using the Monte Carlo technique. The gross weight limits are presented in the form of equations, known as bridge formulas, to be applied on any group of two or more consecutive axles. The results indicate restrictions to the traffic of some vehicles, especially the 740 kN and 19,80 meters length roadtrain. Considering only the serviceability limit state, bridges class 45 exhibit lower weight limits due to the load factors recommended by the code during design.