Design and construction deficiencies of timber railway bridges

Abstract

British and Irish railways once featured several thousand timber bridges and viaducts. Modern and contemporary sources suggest that these structures were replaced due to problems with decay. Consequently, this decay presents a significant challenge to proponents of modern timber bridges, with their critics arguing that timber structures would fail to satisfy the service life requirements. In reality, what actually had a greater influence on their performance and longevity; timber's inherent liability to decay, or deficiencies in their design and construction? This paper presents the findings of the first major study on nineteenth-century timber bridges in the UK, aimed at documenting the design and construction methods used, and their subsequent performance. Despite problems with decay, many nineteenth-century railway bridges lasted beyond their expected design life. Moreover, most problems affecting their life span were the result of erroneous design practices coupled with poor construction and maintenance, rather than inherent material deficiency. Crucially, they could be either obviated or limited through better detailing, modern preservatives and a more judicious consideration of structural forces. These nineteenth-century structures provide crucial lessons in timber bridge design for modern engineers as the profession looks to provide more sustainable infrastructure both now and in the future.