Engineering Wonders of the World
Volume I

THE KOVAL ALBERT BRIDGE. 37 The Ironwork of the Main Spans. Scheme for Floating- the Spans. curved wrought-iron elliptical tube 16 feet 9 inches broad and 12 feet 3 inches high, con- stituting a flat arch, while massive chains were suspended from end to end on either side of the tube. At eleven points in the length of the girder the chains were connected to the tube by upright standards, from which in turn the ironwork on which the track was to rest took its sup- port. This arrangement was especially note- worthy as combining the tubular and chain suspension principles, with the result that the entire structure ;is elegant and substantial in appearance, while the cost was reduced to a minimum—a feature very necessary to suit the finances of the Cornwall Railway Com- pany, its builders. The ironwork was erected on the Devon- shire shore of the river ; and when the first span had been completed, elaborate arrange- ments were made for floating it into position. To do this it was necessary that it should be transferred securely to pontoons, but it was essential that these should be brought to the girder, which was too massive to be embarked in any other way. Accordingly, space for the admission of water was excavated underneath the girder near the ends, and in each of these “ docks ” two iron pontoons were placed. The latter drew about 8 feet 6 inches of water, and were capable of sustaining a weight of 500 tons each, or a total of 2,000 tons, as compared with the 1,100 tons weight of the ironwork. By means of valves, water was admitted into the pon- toons, and they sank on to timbers placed to receive them. Upon each pair of pontoons was erected an elaborate timber framework to support the weight of half the girder. It consisted of stout timber props, some of them 40 feet long, extending upward to the arched tube, and attached to it by iron sus- pension rods, so that when the operation of floating was completed the pontoons would be free to pass away from under the girder. Every part having been tested, extensive preparations were made for moving the pon- This view gives an idea of the size of the arched tubes. toons and their precious load. On this part of the work about five hundred men were employed. Five vessels, obtained from the Government authorities, were moored in dif- ferent positions in the river—one on the eastern side, another in the centre, a third on the western side above the bridge, while the other two occupied intermediate positions. On board were a number of men from the dockyard and sailors Preparations to operate the powerful capstans made, for warping the tube into posi- tion. Four hawsers were also attached to wind- lasses at different points on shore, thus complet- ing the arrangement for guiding and controlling the pontoons in every direction as they floated out from the shore. Able nauiical assistance was also obtained ; while to ensure that his instructions should be clearly understood and immediately complied with, Brunel appointed to each of the vessels one of his assistants as “ captain,” whose duty it was to superintend the men and execute his orders. Signals were given from a platform in the centre of the girder, near which Brunel stationed himself.