Meile & Peter - Mursteg footbridge, Murau 1995. Initially built as part of a timber construction exhibition, the bridge allows pedestrians and cyclists to traverse the Mur river, crossing the body of water and compensating for multiple elevations on each bank through four separate entries. The entire bridge envelope is actually a large scale Vierendeel girder, which unlike a traditional truss that relies on diagonal connections, allows for large rectangular openings. The walls adjacent to the entries of the bridge act as the vertical transverse stiffeners, and the roof and platform serve as the bottom and top chord. This strategy allows for a large opening in the center of the bridge, creating a beautiful picture window that captures the river and surrounding town. These vertical members are also slightly staggered in plan, ensuring that there is diagonal sheer strength while also forming separate circulation pathways for pedestrians and cyclists.
While a traditional Vierendeel girder is constructed with steel, the Mursteg bridge is constructed almost entirely of wood, creating an unprecedented set of technical complications. Each timber element is fastened with a unique method in order to support the structural forces within; the top and bottom chords are made of pneumatically pressed glue laminated wood planks assembled in pieces, which were connected on site with an epoxy glue. The vertical sheer walls were similarly glue-lammed, but then reinforced with a dense nailing pattern. A post-tensioned cable was installed on the lower chord; and in tandem with the dead-weight of the roof, stiffens the entire structure. The complex engineering performed by the architects in conjunction with Jürg Conzett and Kaufmann Holzbau results in a deceivingly simple and beautiful landmark for the town, in which the spatial design is a direct manifestation and expression of the inherent structural properties of timber. Photos © Marghertia Spiluttini.
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