Partners) supported very strongly the Authors' conclusions that, for this type of central development, the cast in situ flat-plate slab was undoubtedly the cheapest, and the quickest to use. It also achieved the minimum depth of deck construction and allowed for the easiest distribution of mechanical, electrical and sanitary services. It had in addition a satisfactory natural fire resistance.73. His own firm was at present concerned with the design of the new town centre at Cumbernauld, near Glasgow, which was roughly 600 ft in one direction and would extend to about half a mile in the other direction. Here, too, flat-plate slabs were being used for the six lower deck-levels.74. The main difference between Cumbernauld and the Elephant and Castle was that whereas the spans at the latter were generally 24 ft, those at Cumbernauld were generally 35 ft and 44 ft. Many different forms of construction, including ordinary concrete beams and slabs, precast concrete, structural steelwork, composite construction, and prestressed concrete had been studied, but for the particular dimensions waffle flat-plate slabs gave the cheapest overall solution to the job.75. The greatest loads carried by the floors at Cumbernauld were those of the construction of the next floor up, and, indeed, as a result, the structure had already been pre-tested, so to speak, with a good load factor. 76. Fig. 21 showed the ingenious method of formwork which had been devised by the contractors, Messrs Duncan Logan. The rib sofits were formed by steel T-sections in pieces generally about 6 ft long. These were supported on special props arranged at 6 ft centres in the two directions. The indentations were then created by fibreglass pans pushed up from beneath. The advantage of inserting the pans from beneath was that after the concrete had been placed the pans were then free to be released first while the ribs were still supported by the T's. 77. Another feature of this formwork system was that the special props gave double support to the waffle ribs. At the end of each prop there was a bearing plate, which formed its own little piece of soffit shuttering, and the main lengths of the steel T s were then supported separately from the props with independent adjustment. This enabled the rib soffits to be struck earlier than the removal of the props, which were required to support the ribs in between.78. The sequence of construction therefore was to set up the props and T's; then to place the reinforcements; then to present the fibreglass pans from underneath; and then to pour the concrete. The pans were then removed by a brief shot of compressed air 48 hours later; the rib soffits were struck at seven days, but the props at 6 ft centres in both directions were left in position for 14 days.79. The Authors were correct in saying that the problem arising from the use of flat-plate slabs was the inflexibility which this could lead to in terms of changed requirements. At Cumbernauld they were trying to meet this point by providing large openings in the floors t...
I would like to pay tribute to the many individuals and organizations to whom we are indebted for co-operation and assistance in bringing this scheme to fruition and to acknowledge the help of our Architect and .our assistants in the office and the site supervisory staff.74. We have also had sympathetic help from the Port of London Authority who have appreciated the difficult problem posed by the nature of the trade effluent in Dagenham. Mr P. A. BanksThe pilot scale trials of secondary treatment of trade waste mentioned in 0 11 have now been completed. With the agreement of the Port of London Authority these trials have been conducted using a section of the full-scale domestic secondary treatment plant.76. The object of the trials was twofold: first, to confirm the practicability of treating trade waste alone, i.e. without mixing it with the domestic settled sewage; and secondly, to find the minimum aeration period that could safely be used. Both these objectives have been achieved.77. The plant was started on a mixture of trade and settled sewage, and in the course of eleven weeks the proportion of trade waste feed was increased to 100%. For eight weeks, whilst the retention period was kept at 12 h or more, satisfactory results were achieved, i.e. the BOD was around 20 p.p.m. under steady conditions. For the remaining weeks of the six month experiment the retention was reduced progressively to 8 h and the BOD figure worsened markedly. During the experiment there was no reduction of ammoniacal nitrogen when running at 100% trade waste. M r J. Perks, Hadsphaltic Construction Co. LtdMy contribution to this discussion is restricted to the construction section generally, and in particular to Contract Cl. The Authors within the text of their Paper have made reference to various management and construction techniques and I feel that it would be of general interest if some were more fully described. 79.In 8 51, the Authors refer to programming and to the use by the Cl Contractor of network techniques, both manual and computer assisted. A major network for the Contract was prepared manually but the resulting programme proved to some extent to be unsatisfactory, inasmuch as structures bearing high float, despite resource restraints, were difficult to position. Upon the major critical structures it became evident that the most effective control could be maintained by restricting detailed programming to construction periods of three months, and it was on these that computer assistance was used. The most successful use of this technique was upon the power wing, where a saving in construction time was directly attributable to the control that the Contractor was able to exercise. 80.In 0 56, dealing with the main power and pumping station, the Authors mention that the cofferdam frames created difficulties in shuttering, and Figs 15 and 17 illustrate this point.That this method of construction was necessary was clearly indicated by the Engineer in his tender documents, but I submit that the opportunity
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