The Iron Bridge - Repairs

Repairs

Just a few years after the construction of the bridge, cracks appeared in the masonry abutments, partly caused by ground movement. Some of the present-day cracks in the cast iron may date from this time, although others are probably casting cracks from defects such as blow holes. Some cracks were pinned with wrought iron straps, but others have been left free. By 1802, the southern stone abutment had to be demolished and replaced with temporary wooden arches before eventually being replaced by iron arches. However, many of the cracks visible in the bridge today have been left untouched. The bridge was over-designed and subsequent bridges, such as those built by Thomas Telford, used much less cast iron. For example, his cast iron arch bridge at Buildwas, upstream from Ironbridge, used less than half the weight for a greater span (130 foot span, 170 tons of cast iron). However, it suffered similar problems of abutment movement and was replaced in 1902.

The cast iron bridge at Coalport downstream, built in 1818, is much more impressive because of its lean, streamlined design, and the higher quality of the cast iron arches. Thus it still carries vehicular traffic, albeit as a single carriageway. It has about half the weight of cast iron as the original Ironbridge, and is longer than the earlier iron structure. It was renovated in 2004 including replacement of the cast iron pavement by lighter equivalents.

More information about how the bridge was built came from the discovery in 1997 of a small watercolour by Elias Martin in a Stockholm museum. This showed the bridge under construction in 1779.

In 1972, a programme of major repairs took place on the foundations of the bridge. It involved creating a ferro-concrete inverted arch under the river. Inward movement of the bridge abutments had compressed the bridge and caused the centre of the arch to rise by a few feet. This counter-arch resists this compressive force from the abutments.

In 1999-2000, the bridge was renovated again, with replacement of the cast iron road plates with steel plates, and a lightweight top surface.

These renovations, together with recent research, revealed more about the building process and the manufacture of the cast iron parts. While the smaller parts were cast using wooden patterns, the large ribs were cast into excavated moulds in the casting sand. It is now known that 70 per cent of the components were made individually to fit, and as a result each is slightly different from the others. English Heritage, together with the Ironbridge Gorge Museums Trust, carried out a full archaeological survey, record and analysis of the bridge in 1999–2000. A half-size replica of the main section of the bridge was built in 2001 as part of the research for the BBC Timewatch programme which was shown in 2002.