Performance of a 20m span stress-laminated-timber arch bridge.

For the past three years the authors have been involved in the optimisation of the performance of stress-laminated-timber arch (SLTA) structures by utilising the strength properties of timber in an arching action for use as vehicle and pedestrian bridges. During this time over 20 permanent bridges have been built and eight have been load tested. The overall aim of this extensive research programme has been to develop structural uses for low-grade, UK-grown, timber and it has been shown that arches, using timber in compression, are an extremely effective technique for bridges. Timber structures have a very high sustainability value while being low cost and employing less early capital. These bridges on public roads can help increase public confidence in timber as a viable structural material. As part of a series of field and laboratory tests on SLTA bridges, a 20 m span arch bridge was designed and constructed at the Glentress Forestry Commission site near Peebles, in August 2004. The bridge has since been subjected to a series of extensive static and dynamic loads evaluating its response to crowd and vandal loadings. The results have confirmed predictions that the strength and stiffness of this type of construction was well beyond the strength normally expected from a slender timber structure. This paper details the construction and compares the analysis, design and load testing of the latest 20 m span full-scale SLTA test bridge at Glentress. The extensive testing programme, augmented by analytical work, aims to develop reliable design guidelines for arch structures using UK softwood