The Perilä and Meriradionpolku bridges

The new residential area in the Vermo area in Espoo relies on a sense of community, concern for environmental factors, good public transit connections and nature as its key elements for attracting residents. A principle feature of the area is the Monikonpuro stream that meanders from east to west among the new residential blocks and parkland areas. The banks of the stream are lined with stairways and places for people to sit and enjoy the scenery. Walking and cycling in the park are a breeze thanks to two light traffic bridges built from wood.

The Perilä bridge is an architecturally ambitious design that creates a modern, but not too serious atmosphere for the area. The bridge demonstrates the modern possibilities of wood construction and conveys a design never seen before in Finland. The lattice design typical of steel structures was successfully borrowed for the wooden bridge, which strengthens the feel of a brand new residential area with its memorable design.

The bridge represents well-established practices in the field of structural engineering. It is a safe and secure structure that meets modern life-cycle requirements. The bridge covering structure essentially consists of a cross-tensioned glulam slabs covered by a glulam framework. No effort was spared to make all the joints as unobtrusive as possible. The ends of the bolts fastening the slats together are hidden by wooden caps.

The upper, load-bearing horizontal structures are protected from UV radiation by a protective metal sheet cover painted the same colour as the glulam to make it undetectable.

The cover slab is creosote-treated GL30c strength class glulam, and the lattice is Grade A salt-impregnated GL30h strength class glulam. The bridge deck wear layer is 38 mm thick salt-impregnated C24 sawn timber fitted into a herringbone pattern.

The stylish handrail on the bridge has a transparent, polycarbonate sheet and meets the strength requirements for bridges with light traffic.

The bridge end supports are steel-reinforced concrete piles driven into the ground with displacement piles.

The bridge has a span of 15.5 metres and an effective width of 4 metres.

Challenges to the design and construction of the Perilä bridge included a 110 kV high voltage line that runs adjacent to the site.

The Meriradionpolku bridge is a balanced and harmonious entity in form and dimensions. The bridge echoes the colours and materials of the Perilä bridge alongside it, but as an adjunct bridge to it.

The bridge design has the same starting points as the Perilä bridge. Unobtrusive connection solutions protect the steel parts from corrosion. The horizontal top surfaces of the lattice planking are protected from the sun’s UV light while leaving the other parts of the glulam lattice visible.

The bridge has a span of 15 metres and an effective width of 4 metres.

In both bridges, the pre-stressed steel rods of the glulam decking are hidden with a protective sleeve that can be detached when needed.

Stainless steel plates cover the wood decking and concrete front wall of the end supports to protect from the stress caused by maintenance work.

Both bridges are rated for a maximum surface load of 5 kN/ m² and 16 ton maintenance vehicles.

The bridge designs leveraged 3D modelling in preparing and harmonising the precise measurements of the details. The strength calculations for the structural elements were based on the Finite Element Method (FEM) structural mode for forces and moments.