Working model of a heavy-duty wooden bridge inaugurated

10.05.2022 Will we be building large infrastructure structures such as highway bridges out of wood in the future? Greater use of timber could help to decarbonise infrastructure construction. Heavy-duty bridges with pre-stressed box-girder elements would enable the implementation of large structural projects such as motorway bridges and viaducts. A working model was built on May 9 in Biel.

Infrastructure construction is one of the biggest sources of carbon emissions in Switzerland. This is primarily due to the use of reinforced concrete. The bridge sector has great potential for reducing CO2 emissions as Switzerland has a high density of bridges – with around two per kilometre on the national highways network – many of which will require replacement over the next few years. The parliamentary motion entitled ‘Research and innovation on timber for use in infrastructure construction as a contribution to decarbonisation’ was adopted by the Council of States and the National Council. The next step is to replace reinforced concrete with CO₂-saving materials, like timber, in the construction of infrastructure. BFH – in collaboration with TS3 and other industry partners – has set out a research strategy for achieving this. A working model was inaugurated on May 9 on the campus in Biel and can be visited.

Feasibility study on heavy-duty bridges

Some initial highly promising methods of using timber in infrastructure projects – such as overpasses for wild animals – have already been implemented. Further research is required to build large bridges – especially those on the axis of the direction of traffic. The Institute for Timber Construction, Structures and Architecture from the Bern University of Applied Sciences BFH is carrying out a feasibility study led by Prof. Dr. Steffen Franke on timber heavy-duty bridges for Swiss national highways and cantonal roads. The development of concrete box girder cross sections using pre-stressed timber technology will be tested from January 2022 to summer 2023. The project aims to determine the box-girder geometry, the tendon profile and local details on force application. The construction process will also be analysed. An initial working model of two modules in a bridge section was created and set up for further analysis as part of the project.

Connected with TS3 technology

TS3 technology enables large surfaces to be made using wood. It took ten years of research from Timbatec in collaboration with BFH and ETH Zurich to develop the technology. TS3 technology is today successfully used in building construction and other applications. The bridge elements displayed here are for a bridge that is transversal to the axis. This will, for example, enable the construction of a cantonal road over a 6-lane motorway with a central support structure (2 x 22.5 metre span with a two-span beam design and a load capacity of 40 tonnes). The individual panels of the elements are rigidly connected using TS3 technology, which improves torsional strength and the efficiency of interaction between the individual panels. For the construction of a bridge, several of these elements can be aligned, connected with TS3 technology and then pre-stressed. The bridge elements are a working model which enables the current details to be evaluated more directly to trial new solutions during the current research project.

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