said that the cost of an underground railway system was very high, but the value of such a system to a city was in fact considerably higher than its direct commercial value measured in terms of receipts from fares. An underground railway in a city was just as important as its sewerage system or fire service; it was essential. In any city with a population approaching one million an underground railway was needed, whether the authorities wished to provide it or not. Efforts were sometimes made to avoid providing it. For example, at Caracas in Venezuela, which had been essentially an old Spanish colonial town, the Government had used bulldozers to knock down buildings and make great straight avenues to enable motor-cars to move faster, but the result had been a great many more motor-cars and the roads were as jammed up as before; so the authorities had had to think again about the provision of underground railways. The cost of such railways was extremely high, but it was impossible to do without them.92. The cost, however, was the real difficulty. The average citizen was compelled to live some distance from his place of employment and to travel there and back on at least 5 days a week. If he lived, say, 12 miles from Charing Cross, the cost was about E40 a year. From nearer the centre, say from Hammersmith or Clapham, it was about f 2 2 a year. Since 75% of the population of Britain earned E12 a week or less, that represented a large proportion of income, yet it was not sufficient to pay for the construction of underground railways. That was the problem. The streets of London were congested with parked cars, and Mr Morgan was convinced that the vast majority of them belonged to people who lived near the underground system but insisted on coming into the centre by road. To take legal proceedings against the drivers would require many hundreds more magistrates! He had been told that 873% of these cars were subsidized to some extent by the employers of those who used them. That pointed to the need for the development of underground railways on a bigger scale than at present.93. Mr Morgan mentioned an underground railway which had been proposed in Calcutta at one time which would have required a passenger density of 10 persons/sq. m or ]/sq. ft. He had suggested that 0.5 person/sq. ft was a more realistic figure and he was shocked to learn that the figure went up to 0.6 person/sq. ft at the worst periods in London.94. Mr Morgan had made an estimate (based on experience with the precast concrete lining used for the main-line tunnels at Potters Bar) of the saving in prime cost by the use of a new type of concrete lining in place of the cast-iron lining. It appeared that the tunnelling costs could be reduced by about 50% by using such a lining for a plain tunnel; it would not be so advantageous with the number of stations on the proposed tube line, and the cost of the whole scheme would not be reduced in that proportion. For the running tunnels, however, such a reduction in cost should be possible. This type of lining, h...

No abstract

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...