Mechanically laminated timber arched suspension bridge

The potential of mechanical lamination of timber for bridge construction and its application in developing structural uses for low-grade, UK-grown timber is investigated. A mechanically laminated pedestrian bridge is designed as a half-scale of a 12 m span bridge and subjected to a series of experimental and analytical investigations. A flat, stress-laminated timber deck is formed by transversely post-tensioning short timber planks with steel bars. The resulting orthotropic solid plate is suspended from two screw-laminated slender timber arches, in which timber predominately acts in compression and end-bearing at the butt ends. The structure is subjected to a series of deck loading conditions up to failure loads. The bridge behaves elastically well beyond its design load, and shows a high level of ductility and recovery capacity. Failure of the structure arises from lateral instability of the arches under symmetrical deck loading. A commercial finite-element analysis programme is used to predict the behaviour of the structure. Close agreement between the analytical and experimental results demonstrates that the structural performance of mechanically laminated timber structures can be reasonably accurately predicted using linear elastic analysis. The study also shows that relatively large-span, stiff, strong structures can be constructed using means of short lengths of low-quality timbe