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Dissertation Medal Winner 2009

The art of skew bridges: The technique and its history explored

Part 2 Dissertation 2009
Rebecca Gregory
University of Westminster | UK
In the nineteenth century, with the advancement of the railway networks across the United Kingdom, bridges were becoming an increasingly necessary part of the industrial landscape. And despite the increased use of materials such as cast iron, many were still constructed of brick and stone.

The masonry arch bridge can be regarded as a relatively simple structure when two systems cross at ninety degrees to each other; however a question arises when the systems cross at an oblique angle. This problem was raised previously in the design of canals, but became more widespread with the railway system due to the increased regularity of its occurrence. The long sweeping curves of the railway line also add additional complexity in contrast to the predominantly straight road and canal layouts: The solution to this problem was the skew or the oblique bridge.

This may sound like a reasonably simple solution and a relatively insignificant piece of civil engineering, but when one attempts to visualise a masonry arch bridge and to consider how the stonework may be skewed to allow for the oblique angle, the complexity quickly becomes apparent. This study looks in detail at one particular solution to the nineteenth century problem of the skew bridge. It is based on a drawing, published in The Builder in 1845, to accompany an article on the construction of skew bridges. An attempt is made here to fully explain this drawing and to investigate the circumstances surrounding its publication.

Importantly, although my dissertation concentrates on one particular drawing, this serves as an example of the way knowledge of descriptive geometry, derived from French military engineering was adapted by British architects and engineers. It also looks at the way nineteenth-century civil engineering structures such as bridges were inevitably appropriated by the champions of British modernism in their search for a functionalist tradition. But also, focussed on the working relationship of two relatively unknown architects, my research also reveals something of their individual professional lives and their place in history.

Rebecca Gregory

Taking as its starting point, an elegant but ostensibly pragmatic drawing from a nineteenth-century edition of The Builder; this study recounts a story that has implications far beyond the modest ambitions of the original publication.

Described is an example of a structure known as a “skew” bridge. A bridge, that is, in which the two transport systems cross at an oblique angle. In the nineteenth century, as a result of expanding canal, railway and road networks, such bridges were, we discover, a common problem for architects and engineers. The challenge was not only structural but also geometric and the drawing analysed in this dissertation describes a technique by which the shape of the various pieces of stone, required to build such a bridge, can be calculated. Explored through a splendidly focussed and rigorous piece of investigative research, the unique qualities and sophistication of this technique are gradually revealed.

At the heart of this research is a reconstruction of the drawing and an investigation of its geometrical construction. Indeed this analysis, conducted through drawings and models, is reason enough to commend this study. But along with the technical analysis, facts about the drawing’s authors and their work are also brought to light. Ultimately it is therefore the picture which emerges of the people and circumstances surrounding this drawing that provides the justification for such a close reading.

Equally important is the way knowledge of such techniques was disseminated and adapted to suit the demands of industrial architecture in the nineteenth century. Yet, although focussed on a particular moment in history, this study is also highly relevant to contemporary practice. At a time when the computer has created an appetite for the kind of formal complexity that descriptive geometry can provide, the drawing for “the construction of skew bridges” reminds us that such interests are a recurring theme.

Combining precise technical analysis and original research (much of which draws on little-known sources), this dissertation offers a unique and fascinating insight into an important aspect of nineteenth-century architectural history.

Richard Difford
Prof Murray Fraser
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