The Influence of Traffic Growth on Bridge Load Effect Forecasting

Freight traffic in Europe is expected to grow by 1.8% per annum until at least 2030. Current approaches for assessing traffic loading on bridges do not generally allow for such growth. This paper presents a methodology which... [ view full abstract ]

Freight traffic in Europe is expected to grow by 1.8% per annum until at least 2030. Current approaches for assessing traffic loading on bridges do not generally allow for such growth. This paper presents a methodology which can model growth in both truck flows and weights when assessing traffic loading on bridges. As an example, the proposed approach is applied to Weigh-in-Motion (WIM) traffic data from a motorway in the Netherlands. Long-run scenario modelling based simulations are used to model different load effects on various bridge lengths. Different levels of growth in both truck weights and frequency are simulated. Time-varying Generalised Extreme Value distributions are then fitted to the resulting load effects to model changes with time. These distributions allow the characteristic 1000-year load effects and corresponding Eurocode alpha factors to be calculated. It is found that growth significantly affects the α–factors for all bridge lengths and load effects examined. Growth in weight has a much more significant effect than growth in flow, with a 1% annual growth in flow causing an average increase in characteristic load effects of 6% for the 40-year service life examined. In comparison, a 1% annual growth in truck weight results in a corresponding increase of 43%. However, there is more uncertainty associated with growth in weight as it is dependent on changes to legal limits and the level of enforcement. The results highlight the need for traffic growth to be considered in the design and assessment of bridges. This will allow the more efficient management of road networks with obvious economic and environmental benefits for road owners.