The behaviour of skewed masonry arch bridges
Masonry arch bridges have been used throughout the world. Many thousands exist in Europe. The number of arch bridges in the United Kingdom has been estimated at 75,000 with approximately equal numbers occurring within the road and railway networks. The arch is very pleasing to the eye. Many arch bridges are listed structures so that replacement schemes are not options. In 1880 Baker was commissioned to report on the deterioration of Telford's Bridge at Over. Baker wrote, "The abutments had gradually gone over, and had been continuing to go over for sixty years. The result was that certain barbarians were actually urging the magistrates to take down the bridge...". He continued, "... cracks in the spandrels were big enough to walk through quite comfortably. It would be a disgrace to the country if they pulled down Telford's historical work and substituted a hideous iron latticebridge", (Heyman & Threlfall, 1973). Masonry arch bridges were built to carry a road, a railway or sometimes a waterway over an obstacle. A right arch bridge was used where the crossing could be perpendicular to the obstacle. In contrast, a skewed arch was built wherever the obstacle and over-road intersected at any angle other than 90°. Thus, a right arch is a special case of the more general class of skewed arch. The extent of existing knowledge of the behaviour of arch bridges is limited to the right arch in which many effects have either been omitted or have been simplified. These effects include the spandrel walls, the backfill, irregular geometry, and eccentric loading. Clearly, there is scope for an advancement of knowledge so that these effects may be considered and ultimately the behaviour of the skewed arch bridge can be described. The construction of arch bridges in Great Britain reached its zenith at around the beginning of the Nineteenth century. At this time, if conditions prevailed, there was a general desire for each new bridge to exceed the span of any that had gone before (Ruddock, 1979). However, Sejourne (1913) could only find eight structures in the United Kingdom that had at least one span with a clear opening of more than 40.0 m.