Hybrid bridge in harmony with nature
For a Danish local authority wishing to build a new bridge over a river in scenic surroundings, a solution that embraced both appearance and function was of paramount importance. The solution chosen was a hybrid structure, which by combining the best of both steel and composites was able to deliver an elegant bridge requiring minimal maintenance.
In conjunction with a new housing development the municipality of Ikast-Brande in Denmark wished to extend an existing path system by building a bridge over a river. During the planning phase the local environmental committee expressed reservations about the impact of a bridge on the attractive river scenery. These reservations were dispelled by opting for a hybrid bridge that would harmonise with the natural environment and at the same time provide the local authority with a durable and cost-effective structure. The new bridge was designed with substructure and parapets of steel and bridge decks and handrails of GFRP.
Integration in the environment
The local authority's first priority was to establish a uniform gravel surface on both the path and the bridge itself. It was therefore decided to weld a cardboard membrane to the GFRP bridge deck, as is also seen on concrete bridges, to protect the deck from friction damage caused by the gravel. All visible surfaces of the bridge were painted a discreet anthracite grey, which together with the uniform gravel surface creates elegant integration between the bridge and its surroundings.
The handrail was executed in fibreglass whose thermal insulation properties create a 'warmer' surface than e.g. steel.
Prospect of future savings
A second priority of the local authority was that the bridge should be durable and require only minimal future maintenance. The decision was therefore taken to use fibreglass, a tough material that not only provides a no-maintenance bridge deck, but also creates watertight protection for the steel substructure, thus extending the service life of the bridge as a whole.
As the bridge is situated near a major road and may therefore be exposed to traffic, the bridge deck used was FBD300, which is stronger than the specification for footbridges. The bridge deck was secured by bolts to the substructure of galvanised steel.
Light weight and easy assembly
In order to avoid damaging the ground around the river during the bridge installation the GFRP bridge deck was offloaded from the main transporter and taken to the site on smaller loaders. Glass fibre is a lightweight material which is easy to machine, and the final adjustments, such as drilling of bolt holes, were performed on-site.