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Timber-Trough Bridges

Trough bridges in timber construction

Trough bridges are especially suitable for span widths of up to 35 m

Trough bridges are constructed from two main girders made from laminated timber which are arranged at the railing level. Reinforcing frames made from steel are fitted between the main girders at a distance of approx. 2.0 m. Both open and sealed road surfaces can be added to the steel cross beams. As a rule, the horizontal reinforcement is completed in the form of a round steel lattice. To ensure a long service life, all of the supporting timber elements have casing on their top and their side.

Trough bridges offer a good cost-benefit balance with a visually appealing appearance. They are frequently used as single span bridges.

Attributes of trough bridges:

  • especially cost-effective type of bridge
  • supporting system consists of two glue-laminated beams at the railing level
  • a variety of surface configurations can be used (timber decking, GRP decking, mastic asphalt, natural stone slabs, etc.).
  • bridge type can be delivered to the construction site completely ready made and assembled within one day
  • the casing on the top and side of the girders ensures the optimum protection against weathering

Protected main supporting structure

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*. On a trough bridge, the main supporting structure – consisting of two girders made from laminated timber – is protected by side cladding in the form of solid timber and a top cover made from sheet metal.

* Source: Redemption amounts calculation regulations – ABBV, BMVBS, status 2010 and study of DGfH 2006

Advantages of the trough bridge:

  • high cost-effectiveness due to simple construction type at extended lengths
  • main girders are well protected against weathering
  • main girders reduce the height of the required railing
  • high level of prefabrication
  • any road surface configuration possible


Here is a selection of laminated timber trough bridges.