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Description of the Design—Abandonment of the Works, 1853
The span of the bridge is greater than that of Mr. Brunel’s design for the second competition, but much less than the spans of the earlier designs, to which he had given the preference. [1] On this point, as well as on the question of site, he had to conform to the wishes of the trustees. [2] The span approved of by them necessitated the building of a very large abutment on the Leigh woods side, the height of which, from the surface of the rock to the level of the roadway, is 110 feet. Above the roadway, the tower to carry the chains is built to a height of 86 feet. On the Clifton side, the base of the tower is formed by one of the boldest of the range of St. Vincent’s rocks, which here rise almost perpendicularly to a height of 230 feet above high water, and consequently a very small abutment was required. The tower on this side is 3 feet higher than that on the Leigh woods side, and the roadway has a general inclination of about 1 in 233. Mr. Brunel thought that if the roadway were level, it would have the appearance of falling towards Clifton, owing to the ground there being precipitous, while on the Leigh woods side it is sloping.
He intended, in the construction of the bridge, to have followed out the ideas embodied in his report of 1829, and would have preferred to have had only one chain on each side of the bridge, and that much stronger than was usually adopted; but, in deference to public opinion, he put two chains, though he doubted if they would expand equally. ‘A rigid platform would in some degree prevent the unequal distribution of load thus caused, but he endeavoured to lessen the effect of unequal expansion by arranging a stirrup at the top of each suspending rod, so as to hold equally at all times on both chains, and thus to cause each to sustain its proportion of the load.’
The road platform was to have had beneath it ‘a complete system of triangular bracing, which would render it very stiff.’
In order to lessen the action of wind on the bridge, he brought down the main chains in the centre nearly to the level of the platform, and intended to apply the system of brace chains at a small angle to check vibration. There were, moreover, to be two curved chains lying horizontally, and attached underneath the platform, so as to resist the lateral action of the wind. [3]
He here introduced movable saddles to carry the chains on the top of the towers, with rollers running on perfectly flat and horizontal roller beds. [4] By this arrangement no pressure except a vertical one could come on the towers.
He also devised means, by levers and hydraulic presses, for relieving the rollers and roller beds from pressure, in the event of their requiring renewal.
Mr. Brunel ultimately determined to adopt the Egyptian style of architecture. His brother-in-law, Mr. John Callcott Horsley, R.A., gives the following account of the proposed designs for the towers:—
‘His conception of the towers or gateways at either end of the bridge was peculiarly grand and effective, as may be seen from his sketches still existing. They were to be purely Egyptian; and, in his design, he had caught the true spirit of the great remains at Philæ and Thebes. He intended to case the towers with cast iron, and, as in perfect accordance with the Egyptian character of his design, to decorate them with a series of figure subjects, illustrating the whole work of constructing the bridge, with the manufacture of the materials—beginning with quarrying the iron ore, and making the iron, and ending with a design representing the last piece of construction necessary for the bridge itself. The subjects would have been arranged in tiers (divided by simple lines) from top to bottom of the towers, and in the exact proportion of those found upon Egyptian buildings. He made very clever sketches for some of these proposed figure subjects, just to show what he intended by them. I remember a group of men carrying one of the links of the chainwork, which was excellent in character. He proposed that I should design the figure subjects, and he asked me to go down with him to Merthyr Tydvil, and make sketches of the iron processes. We accomplished our journey, and all the requisite drawings for the intended designs were made.’
The works were commenced with the Leigh abutment, which was completed in 1840, great delay having been caused by the failure of the contractors. This misfortune led to a large excess of expenditure over the original estimates. In 1843 the whole of the funds raised (amounting to 45,000£) were exhausted, and there still remained to be executed the ornamental additions to the piers (the cost of which was estimated at about 4,000£), half of the iron work, the suspension of the chains and rods, the construction of the flooring, and the completion of the approaches, &c., the estimate for the execution of which was 30,000£.
Unfortunately, all efforts to raise further subscriptions were unsuccessful; and in July 1853, when the time limited for the completion of the bridge had expired, the works were closed in, and the undertaking abandoned. [5]
[1]
| Span | 702 | feet 3 inches. |
| Versed sine | 70 | “ |
| Roadway above high-water | 248 | “ |