Calibrating Eurocode's Fatigue Load Model 3 to Specific National Traffic Composition

Accuracy in design of steel and composite bridges against fatigue is strongly connected with the distinct features of regional traffic. However, the approach followed by Eurocode 1 (EN1991-2) barely differs among European countries as far as fatigue load models are concerned. The recommended fatigue load model in Eurocode is FLM3. It is easy to use, but it has to be calibrated for each region where it is applied if major differences in traffic composition exist (especially regarding the distribution of heavy vehicles, the traffic volume and the vehicle types). This paper takes into account the particular aspects of Finnish traffic through extensive recorded traffic data covering the whole Finnish road network. It examines and evaluates the influence of essential factors, through the available data, in fatigue design. Results of the study for steel and composite bridges, according to EN1993-2 and EN1994-2, respectively, are summarized in simple rules, additional to the basis of Eurocode 1, at the Finnish National Annex of EN1991-2, so that the level of safety is assured against the actual Finnish traffic conditions. Besides the locally oriented nature of the composed criteria, this attempt to quantify and build-in the codes fatigue's primary features could also be used as an initial guideline for future attempts for any road network.