The Iron Bridge: desk study and engineering assessment

The Iron Bridge in Shropshire was a pioneering structure. Constructed in 1779, it was the first iron bridge in the world. Its unique semi-circular shape creates an elegance when reflected in the river, yet it is essentially the wrong form for a cast-iron engineering structure, being highly redundant and unable to accommodate the significant movement that has occurred in the Severn Gorge at this location. This has led to the many crack defects that now exist in the ironwork. This paper outlines the work undertaken for custodian English Heritage in both researching the history of defects in the bridge and modelling and assessing the present-day structure. It looks at the long history of repairs on the structure. It describes in summary the extensive process of surface and solid modelling and advanced analysis undertaken to assess the current capacity. It concludes that, although many predate modern conservation practice, the bridge repairs have essentially followed good conservation principles and that sufficient capacity exists to assure continued public enjoyment of the bridge.