DiscussionMr Rudolph Glossop observed that the design of the transit shed a t No. 19 Berth, Eastern Dock, London Dock, was based on a three-hinged portal frame, and so far as he knew, it was the first structure of its kind to be built in Great Britain. He then displayed a series of slides illustrating some practical details of its construction.Each portal frame was composed of four comparatively simple precast units-two top booms and two vertical booms-the maximum weight of any unit being 3-1 tons, which was well within the capacity of an ordinary mobile crane. The vertical booms could be handled without prestress, but the top booms were designed to be stressed before removing from the casting bed. On the whole, those members had been found quite easy to handle on the site, although it had been necessary to be very careful to use the correct lifting points on the top boom. Those were at 2 feet from the tapered end and 9 feet from the outer end. As could be seen from the first slide, that construction gave a span of 74 feet and plenty of head-room clear of obstruction, so that it was well suited to a building in which cargo was to be moved and stacked.All the members had been cast on the site, the concrete being mixed in an ordinary 10s mixer and barrowed to the shutters. The mix had consisted of 5$ cubic feet of coarse aggregate (4 -3 inch), 4 cubic feet of moist sand, and 2 cwt of Portland cement. The water/cement ratio had been 0.3, so that about 1 gallon of water had been added for every bag of cement. It was interesting to note that the natural water-content of the aggregate was usually about 14 gallon per bag of cement, so that slight variations in the natura1 moisture-content of the aggregate had been important and careful site control had been necessary.The results obtained from that mix had been :Strength at 3 days (average value) : 4,720 lb.
The Royal Portbury Dock, Bristol F. IRWIN-CHILDS, W. J. SlVEWRlGHT 81 P. T. SHAW Messrs Irwin-Childs, Sivewright and Shaw Among the interesting features in the scheme not fully dealt with in the Paper are the unusually large mitre gates with their unique action which has enabled the range to be extended. The latest comparable examples of locks built in Europe and Russia are all reinforced concrete cantilever structures of conventional form and proportions, built in open excavation in the dry, with a concrete volume ranging from 2 to 4 times that of Portbury. Indirect savings arose from the overall concept at Portbury and particularly from major excavation and filling executed in the dry.71. There were constraints imposed by the largely rural site which nevertheless carried a number of public utilities which had to be maintained. 72.In the diaphragm work the closeness of the bond between soils and concrete was illustrated by the appearance of the walls after exposure. The greater thickness of the overlying silts was largely discounted when assessing the resistance to overturning of the structure, greater reliance being placed on the mart, the quality and dryness of which were shown after excavation of the cross-lock tunnels and the circular arch cofferdam.73. There were no fatalities among the labour force over the 5 year construction period.M r A. J. S. Mansfield, Edmund Nuttall Ltd The.diaphragm walling contract at Bristol, on which I was agent, represented about 1% of all the world's diaphragm walling then constructed and was the largest single contract let for the Royal Portbury Dock.75. My comments will be confined to construction details. The contract was undertaken by the joint venture of Edmund Nuttall Limited and SIF Entreprise Bachy of Paris. Possibly the greatest contribution to success made by Bachy was the grab which they brought to Bristol (Fig. 17). The characteristics which are noteworthy are the rope suspension, giving speed and simplicity of operation, and the long body which provided vertical directional accuracy so essential to the diaphragm walling operation. The grab dealt successfully with both the hard and soft ground found at Bristol.76. There were 500 reinforcement cages in the contract which were necessarily constructed horizontally on the ground, and had to be lifted to a vertical position to place them within the trench. The danger of permanently distorting a cage during lifting was overcome by providing adequate bracing within the cage, by using a stiffening strong back frame externally and by utilizing two cranes to carry out the lift.77. I should like to ask the Authors whether, with the benefit of the experience gained on other contracts since 1973, they would now adopt a different configuration for the panel layout, and in particular perhaps incorporate a shear connector such as the type used at Redcar.
At what stage of the work were the archaeological discoveries made? Presumably there were discussions between the Iraqi Ministry of Construction and the organization responsible for archaeological preservation. It would be of interest to know whether the Engineer was consulted on this matter and, for example, if he was allowed to give consideration to the possible redesigning of the bridge, perhaps by increasing the spans, to avoid destruction of the ancient brickwork. M r P. L. Martin, Rendel, Palmer & TrittonThe foundation design for the bridge was dominated by consideration of the extraordinary scour conditions. Design studies therefore centred on pile capacity under both vertical and lateral load at times of flood. This discussion contribution enlarges on the pile testing which was camed out. 45.The first two pile tests did not confirm either that the permanent piles would have adequate bearing capacity or that settlements under working load would be within acceptable limits. A further test was made. The test had two objectives. The first was to prove the effectiveness of the unorthodox procedure for cleaning the base of the pile shaft. The second was to determine the relationship between end bearing capacity and the standard penetration test data obtained from the site investigations. An extrapolation could then be made to determine base capacity under scour conditions. Ideally this test would have been made on a pile founded at -9.0 m, but, even if skin friction could have been eliminated entirely, it would have been necessary to increase the test load to compensate for the increased overburden pressure (from +5.0 m to river-bed level) over that occurring at maximum scour. Furthermore, a test pile could not by then
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