Simulation of traffic loading on long span bridges

Existing long span load models have typically been developed using a number of conservative assumptions, and as such are more applicable to the design of new bridges rather than the assessment of existing structures. Excessive conservatism in such assumptions can lead to expensive and unnecessary interventions in existing bridges. Furthermore, existing load models do not always allow for correlations in traffic weights and vehicle positions on the bridge. This paper introduces a method of simulating the load effect on long-span bridges, termed 'Long Span Scenario Modelling' (LSSM). The scenarios are blocks of vehicles extracted from a congested traffic stream that contain the inherent correlations between vehicle weights and positions. For long-span bridges, the combination of vehicles, such as platoons of Heavy Goods Vehicles (HGVs), has a greater influence on bridge loading than individual heavy vehicles. The scenario modelling approach allows for these critical vehicle combinations. Weigh-in-Motion (WIM) data from a site in the USA is used to demonstrate the process. The LSSM is shown to better represent the long span load effect when compared to measured traffic, particularly when the correlation between successive scenarios is accounted for.