M r BrownIt was interesting to examine Rennie's structure during demolition. Although the bridge was extensively cracked the workmanship was first-class. Telford's opinion of the safety of Rennie's bridge has clearly been vindicated but the clay beneath the foundations was grossly overloaded and the factor of safety at foundation level must have been very low throughout the life of the structure. existing buildings most careful consideration had to be given to safety. I would like D2. Although there was just enough room for the new bridge structure between t o pay tribute to the Contractor's skill and safety record during this work which has proceeded without a fatal accident to the public or to the workmen, and the bridge has been completed without any detrimental effect to adjacent structures.
D3.The most delicate operation during stressing of the superstructure was hanger rod adjustment since the gantry and new beam deflexions were varying by several inches as these operations proceeded. These movements were greater than the ultimate load extension of the temporary hanger rods and after some difficulties with the first box during which one or two of the hangers broke, continuous monitoring by electrical gauges was employed.D4. As expected, creep strain of the superstructure and other small movements the end of the maintenance period by which time the youngest box member will behave not yet ceased and it will be necessary to re-set the main expansion joints about nearly two years old. There has been some minor internal hair line cracking in the box members, in particular at the lateral concrete diaphragms. . During construction of the first box the diaphragms were generally cast in situ and shortly thereafter restrained against shrinkage by post-stressing against the adjacent concrete box units.diaphragms in subsequent boxes.Minor shrinkage cracking ensued but this problem was greatly reduced by precasting
I should like 10 explain how the Paper came to he written. the context of design competitions. I thought that in a cnmpetitinn a number of 62. A few years ago it occurred to me that one might he able 10 study dcsign in alternatives would be proposed and justified as meeting a given design situation. I Posals submitted and I supposed that one might be able to see general principles anticipated that an argued judgement would then be made on the merits of the p~o -emerging which could form the basis of a university course in design. a competition there.It proved, however, a rewarding choice from three aspects.
63.The choice of Clifton was fortuitous: I merely knew that I. K. Brunel had won First, it was possible to study both sides of the project. The minute hooks of the Secondly, the Clifron project belongs to a period of rapid development of suspension Clifton Suspension Bridge Trustees have survived as well as the records of Brunei.-notably in France-there was a considerable blossoming of this particular form of bridges. At first in the United States, subsequently in Britain and on the Continent structure in the first half of the 19th century. Thirdly, the study introduced me not only to the work of Brunel and his contemporaries but also to their personalities.Mr P. S. A. Berridge, formerly Assistant Encineer (Bridges). Rritish Reilways.
Wcstcrn RcgionIt is incorrect to say Brunel designed but one olher suspension hridge, the Hungerford Bridge, besides Clifton (5 6). The so-called truss spans of Brunel's famous railway bridges at Chepstow and Saltash were in fact suspension bridges.spans, separate for each railway track) was opcned in 1852. In the two longer spans, 65. The bridge across the River Wye at Chepstow (one 308 ft and three 100 ft Brunel used riveted wrought iron tubes, 9 ft in diameter, as struts to counter the inward drag of the ends of the suspension chains (Fig. 9). The tubes were not selfsupporting. Fabricated on the low ground on the right bank of the river, each tube was built with a camber of 18 in. at the centre and was temporarily trussed prior to being launched across the river and hoisted more than 100 ft to the tops of tall Engineering Co.'s Seville Works in Dublin; on the limeslone cliff on the left bank of towcrs. On the river picr the tower was built of cast iron, imported from The lrish iron tower, and nn the rnasonry~they rested nn rollers.the river, the tower was of stone masonry. The tubes had fixed hearings on the cast 66. Once each tube had been set on its bearings, Brunel completed the erection oi the slruclural framework; two verticals and the plate girders which carried the
M r GowringThe Severn Bridge had two features which were unusual for a major bridge. First, all three foundations in the river which were submerged at high water were exposed at Papers published: Proc. Insrn c h . Engrs, 1968, 41 (Sept.) 1-104. 545 Downloaded by [] on [12/09/16].
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