Overview Fatigue Phenomenon in Orthotropic Bridge Decks in the Netherlands

An orthotropic steel bridge deck is a construction type with advantages. It is a lightweight construction, which is beneficial especially in case of larger spans. However over the last decades several details showed fatigue cracks. Well-known examples of fatigue cracks in the Netherlands are those observed in the bascule bridge Van Brienenoord in Rotterdam in summer 1997. Due to the huge amount of heavy vehicle traffic at the highways and the heavy but still growing axle loads, several fatigue cracks have already been observed in bridge decks and more cracks are expected. A lot of orthotropic steel bridge decks in the Netherlands are build up in the sixties and seventies. Fatigue problems are nowadays a challenging problem for bridge engineers. This introductory paper describes several fatigue prone details. Especially four types of cracks are discussed in this paper. These are cracks in the deck plate (1), cracks in the longitudinal weld between deck plate and longitudinal trough profile (2), cracks in the trough splice joint (3) and cracks in the connection between the trough profile and the crossbeam (4). For those four crack types the mechanical background is briefly analysed. The description of the cracks is illustrated with visual observations of the cracks in the steel structure it self and also with visual observations of the surfacing layers. The analysis of these structural details leads to the conclusion that especially fatigue cracks in the deck plate are potentially disturbing the traffic flow. For this reason emphasis on solutions for this type has been made. The analysis also leads to conclusions that are useful for the development of improved bridge deck structures. History In the third decade of the 20 th century, engineers in Germany and the USA were searching for an alternative to wooden and concrete decks supported by stringers and crossbeams. They considered steel decks as a promising alternative. The objectives were cost savings by a reduction of the steel mass and also achieving a reduction of