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European road freight transport has increased by 38% between 1995 and 2005 and this strong growth trajectory seems likely to continue into the future. To address this growth without compromising the competitativeness of European transport, some countries are contemplating the introduction of longer and heavier trucks, with up to 8 axles and gross weights of up to 60 t. This has the advantage of reducing the number of vehicles for a given volume or mass of freights, reducing labour, fuel and other costs. However, many roads authorities are concerned about the implications for Europe's bridge infrastructure. For bridge loading, it is the combination of gross weight and truck length that determine load effects such as bending moment and shear force in the deck. A probabilistic analysis is required to assess whether these proposed trucks will lead to greater maximum lifetime (characteristic) load effects. If this was found to be the case, it would necessitate the strengthening of a great number of vulnerable bridges throughout the continent or it could even prevent the introduction of heavier trucks. This paper reviews the factors governing traffic loading on short/medium span bridges. There is considerable conservatism in the Eurocode traffic loading model. Hence, bridges designed to this or similar modern codes of practice can be shown to be safe in the presence of significant numbers of longer and heavier trucks. Even more significantly, using data from one of Europe's most heavily trafficked highways, it is shown that the critical loading events are often special permit trucks such as cranes or low-loaders with up to 12 axles. Hence, characterisitic load effects (bending moments etc.) are unlikely to be strongly influenced by the most common truck type- 5-axle articulated trucks- and are therefore unlikely to be affected by the introduction of longer and heavier versions of them.
Caprani, C., Enright, B., O'Brien, E.: Implications of future heavier trucks for Europe's bridges. A. Znidaric (ed) Transport Research Arena Europe, 2008, Ljubljana, Slovenia. ZAG, Slovenian National Building and Civil Engineering Institute,; DDC Consulting and Engineering Ltd; DRC, Road Transportation Research Association of Slovenia. 2008.