Traffic load patterning on long span bridges

For highway bridges, current live load models typically replicate the effects of real traffic streams at a certain return period. Most standards stipulate that the worst load effect should be considered, obtained by patterning the live load on the adverse portion of the influence lines only. Certainly, this is a worst-case scenario, but real traffic does not pattern in this manner. This paper examines design standards' approach to load patterning against the behaviour of real traffic. Traffic microsimulation is adopted on a generic 1200 m bridge. We consider the possible road topologies that might give rise to design standard loading patterns. The results show that real traffic cannot achieve the code-inferred traffic pattern. The load effect results are extrapolated to represent assessment and design return periods. A possible road topology is put forward, and it can be the prototype of a new method to assess the load effect.