Road bridges are subjected to millions of cycles of heavy vehicle loading over their design lives, and the introduction of higher vehicle mass limits on New Zealand roads will significantly increase the rates of fatigue damage in bridge superstructures. The NZ Transport Agency's Bridge manual has relied on British and Australian standards for fatigue design criteria, and the aim of this project was to provide the basis for amended fatigue loadings based on New Zealand heavy vehicle characteristics, with allowances for forecast long-term growth in volumes and vehicle masses.
The base fatigue loading was derived from analyses of effects on bridge spans of heavy vehicles recorded at weigh-in-motion sites between 2007 and 2011. The base fatigue loading was then adjusted for increases in legal vehicle masses permitted under a 2010 Land Transport Rule amendment (introducing HPMV – high productivity motor vehicles).
The recommended fatigue design vehicle is a 54-tonne 8-axle truck-and-trailer, which represents the dominant freight vehicle on New Zealand roads scaled up to full HPMV higher mass limits. Cycle counts for this vehicle were derived to fit New Zealand routes and growth forecasts. Factors enabling the continued use of the Australian fatigue design vehicle are included.
Other recommended fatigue design criteria draw on the Australian and Eurocode bridge design standards.