Evaluation of pedestrian timber bridges in the city of Hamburg with particular consideration of design detailing

Since 1997, the use of wood in bridge construction has been increasingly criticized by the Hamburg Federal State Authority due to its perceived shorter service life as a result of decay. Wood research, however, often suggests that wood is suitable for weathered structures as long as structural wood protection is observed. In order to unravel the reasons for the reduced service life in Hamburg, several bridges were examined by visual assessment, focussing on decay and especially on design. Through this inspection, details of designs affecting the durability of individual bridge components and favouring the propagation of damage, as well as subsequent decay, were detected. In this respect, faulty engineering and insufficient structural wood protection are considered as the main causes of the short service life experienced in Hamburg. Giving examples of pedestrian timber bridges, this practical report illustrates several essential errors in protective design that are still being made in the planning and construction of naturally weathered timber structures.