Stress ribbon bridges are characterised by a roadway that features a slight dip. Due to this dip, the cross section is subjected to tensile stress and optimum use is made of the supporting cross section. The high tensile forces on the abutments have to be carried by the foundations. This generally occurs on the basis of deep foundations with post anchoring.
With its high tensile strength in the fibre direction, timber is an ideal material for constructions of this kind.
Structural timber protection is the key to the longevity of a timber bridge. Structural timber protection intends for all structural timber components to be completely protected. In this respect, the following steps are taken into consideration: Installation of technically dried timber with a timber humidity of 12% in order to prevent insect infestation, protection against weathering, ingress of moisture, UV rays due to the installation of projections and skirting in the design as well as good air circulation to encourage drying out. Constructions designed in this way satisfy the requirements of protected timber bridges pursuant to DIN EN 1995-2 NA. This means that loss events are prevented and maintenance costs are minimised, and the use of timber preserving chemicals can be reduced and/or avoided. Structures protected according to DIN EN 1995-2 have a service life of 60 - 80 years*.
* Quelle: Ablösungsbeträge-Berechnungsverordnung - ABBV, BMVBS, Stand 2010 bzw. Studie der DGfH 2006
Here is a selection of stress ribbon bridges with timber supporting structures.