Ynysgau Iron Bridge
in Merthyr Tydfil
DEMOLISHED IN 1963. Many parts saved and held in storage by Merthyr Tydfil Council.
Designed by Watkin George, it features his distinctive heart-shaped motifs (on the central parapet castings). Built in 1799-1800[1]. A suggestion of a heart shape also appears on cast iron handrail posts on the Watkin George's Pontycafnau Bridge, and the motif appears on the Melingriffith Water Pump.
Many of the parts were saved after demolition, and it is hoped that the bridge will be assembled in whole or part in recognition of its historical significance. Not only was it one of the earliest cast iron bridges, it is of a bold and unique design. Subsequently cast iron bridges tended to follow a familiar pattern, with curved arches for road (and later rail) bridges, and flanged cast iron plates in the case of aqueducts.
Photographs of some of the surviving components are available here. Some of the castings are clearly broken, but it is not clear how much of this damage occurred during demolition, as it is known that some of the castings had been broken and repaired when the bridge was in use.
An account of the history of the bridge was written by Leo Davies and published in 1978[2]. The bridge, of 66 - 68 ft span, was of relatively lightweight construction, and was a bold design. It was nominally slightly arched, although the 'arch' comprised three nominally straight sections (although each section had aslight rise towards its mid span: the centre section had a rise of 4 inches in the middle, the overall length being 22 ft 6"). The side castings were not bolted directly together, there being oak packing pieces between the vertical faces. These would have helped to absorb shock and damp out vibration, but the flexibility would have resulted on varying loads being felt by the bolts.
1963 photos of bridge shortly before demolition here show that at that time the road metal had been removed, exposing the numerous cross girders. Another 1960s photo seems to show the presence of stone setts on the deck. Recent photos of the parts in storage show that the cross girders are of thin inverted T section. The vertical web rises slightly towards the centre. On each side of the web, at the centre and near each end, there is a boss with a vertical dovetail groove. It would be presumed that these were to accomodate connectors to join each cross girder. However, there is no evidence to suggest that connectors were used. A 1940s photo, taken when the bridge was in use, shows that the cross girders were not covered at that time - the spaces between the webs were filled with some unidentified material (possibly fine slag?), and the tops of the cross girders were exposed. These cross girders were probably installed when the bridge was repaired in 1817, the repair bill including the large some of £196 11s. 6d for castings.
Photos of the original side member castings show that they had been cast in open moulds, with numerous craters in the upper surface caused by gas bubbles rising to the surface of the molten iron.