Abstract
Fatigue load models for road bridges given in the Eurocode EN1991-2 have been calibrated considering real traffic measurements that became available around 1990. Since then, traffic composition has evolved considerably, also considering the issuing of the 96/53/EC Directive, which legitimated member states, on an equal and not discriminatory basis, to allow the circulation of Long and Heavy Vehicles (LHVs). Thus, the appropriateness of fatigue load models to cover also the effects of these vehicles, which are longer, heavier and potentially more damaging than common Heavy Goods Vehicles (HGVs), became an issue. The aim of the study is to assess how the evolution of European traffic influences the fatigue assessment of bridges. To capture the essence of the problem, three different real traffic measurements are compared in terms of fatigue damage: the Auxerre (FR) traffic, adopted to define fatigue load models in EN1991-2; the Moerdijk (NL) traffic, characterized by a high percentage of LHVs; and the Igualada (ES) traffic. To assess the current relevance of fatigue load models LM2 and LM4 of EN1991-2, the aptitude of these models to adequately reproduce the effects caused by LHVs is discussed in detail. The results demonstrate that the Auxerre traffic is still the most onerous; that the Moerdijk traffic is generally more severe than the Igualada traffic, and that the fatigue load models of Eurocode do not require major updates. The study is further supplemented by investigating the suitability of the formulae provided in the Eurocodes for the damage equivalence factors λ2 and λ3 to express the influence of the total lorry volume on the fatigue damage. In that latter case, the conclusion is that the formulae proposed in the Eurocodes, based on the assumption of a linear fatigue strength S–N curve with constant conventional slope m, could lead to erroneous, even unsafe, estimates of the fatigue life, especially when details are characterized by constant amplitude fatigue limit ΔσD, thus calling for further improvements of the formulae themselves.
Highlights
In consequence of the 96/53/EC Directive, some European countries allow the circulation on their respective road networks of Long and Heavy Vehicles, characterized by length and weight going beyond the limits imposed on common Heavy Good Vehicles
Considering that traffic loads on road bridges provided in EN1991-2 were defined and calibrated using the traffic recorded in Auxerre, which is very severe, but does not include Long and Heavy Vehicles (LHVs), their introduction could significantly impact the design of new bridges, but especially the assessment of the existing ones
To discuss the consequence of circulation of Long and Heavy Vehicles on fatigue design of European bridges, the fatigue effects caused by the long-distance traffic recorded in the Netherlands (Moerdijk), characterized by a high percentage of LHVs, have been compared with the effects caused by Auxerre traffic and with those produced by fatigue load models load model no. 2 (LM2) and load model no. 4 (LM4) of
Summary
Being characterized by a high percentages of articulated lorry typologies and by low percentage of lorries with trailers, the Auxerre traffic composition was reckoned to be well representative of the expected lorry traffic trends in continental Europe around the 2020s. For this reason, static and fatigue load models included in EN1991-2 [1] are mainly based on it.
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