wrote that since the initiation of the work described in the Paper more information on the rate at which concrete dried had been obtained at the Central Electricity Research Laboratories, Leatherhead. Moisture gauges, similar to those mentioned, had been placed in two large concrete structures, one being the biological shield at a nuclear power station, the other a 6 ft dia., 7 ft block of concrete in the laboratory. Readings from these gauges had been taken for over 5 years at ambient temperatures and for 13 years at higher temperatures. Fig. 12 gave a plot of the moisture gradients obtained and this indicated that, even after 5 years, the depth to which significant drying expressed as loss of evaporable water had occurred was not greater than 2 ft. These results were obtained from the difference between an active gauge and a sealed control gauge kept under the same temperature conditions for the same period. It had been found that the sealed gauges indicated an apparent moisture loss of about t% per year (expressed as the dry weight of the gauge). Quite possibly the dryingout referred to in § 44 was this 'loss' and the actual reduction in the moisture content of the concrete was much less. Fig. 12 were under ambient temperature conditions (16" k4"C). If the temperature was increased, the rate of drying increased considerably. Fig. 13 showed the effect on the moisture loss 3 in. from the surface of 5 year old concrete when the temperature was raised from an average of 20°C to an average of 36°C. Dr B. Mayfield (Civil Engineering Department, University of Nottingham) suggested that from 5 95 et seq., it would appear that the future of concrete turbo-blocks was in the balance and that one of the principal reasons for this move away from the Appendix stated that low-tuned concrete blocks 'would involve an unusual degree of use of concrete was because of the 'uncertainty as to the value of E (dynamic)'. The concrete quality control and the most accurate determination of elastic constants '. 107. The results shown in

The C.E.G.B. are installing single shaft turbo-generators of 500 and 660 MW with solid coupled shafts. It is important to assess the extent to which the operation of these large machines might be affected by changes in alignment resulting from differential movements in the turbo-generator blocks. The paper sets out the development of turbo-blocks against the evolution of turbo-generators and associated plant; and discusses the problems which have emerged as a result. The authors investigated 12 existing reinforced concrete turbo-blocks in the 120-200 MW range to establish the extent and cause of differential movements in the concrete and their resulting effects on the machine. Level measurements were taken over a period of about three years on the machine floors and basements of these blocks. These readings were correlated with changes in concrete temperature, moisture content and variations in ambient conditions. Conclusions are drawn from the investigation which can affect the design and construction of concrete turbo-blocks and particularly certain procedures for machine alignment. The continued investigation on the 500/660 MW blocks now under construction is described, as well as methods adopted for the better distribution of heat in the turbo-blocks. Current procedures for design and construction of turbo-blocks are reviewed, relative merits of concrete and steel blocks compared, and the changing roles of plant manufacturer, civil engineer and block contractor/manufacturer considered. The tentative views formed by the authors from this study, from continental sources and from their discussions with power station superintendents and staff are submitted for discussion.

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Partners) wrote that the presentation of this Paper by Mr Rae and of a similar Paper by Mr Keith served the useful purpose of emphasizing the need for a thorough examination of the incidence of vibrations in turbo-generator foundations. With the rapid increase in size of plant in the past two decade$ the risk of incidence had increased markedly and greater reliance had to be placed on the satisfactory operation of individual machines. 83. On the other hand, German engineers had been obliged to make a much more theoretical approach owing to the work over many years of Dr E. Rausch, and of others, which had led to the issue of DIN.4024. From a private English translation of part of Dr Rausch's book, 'Maschinenfundamente und Andere Dynamisch Beanspruchte Baukonstruktionen', it was impossible not to be impressed by the extraordinary thoroughness of the German methods and by the many ingenious approximations used to overcome the more intractable complications. 84. Nevertheless, the German methods, which carried much conviction by their superficial clarity, required very critical application to a particular foundation; they were developed for much smaller foundations than was now common practice in power stations, and there seemed to be grounds for doubting if the conclusions reached by a design engineer, well versed in the disciplines of structural design and using these methods, could bear close resemblance to conditions in practice. The British Standard Specification 85.It was for this reason that a suggestion was made recently to the Central Electricity Generating Board that a programme of research on the vibration of turbogenerator blocks should be undertaken. The suggestion, which was accepted, included the following proposals :(U) to observe thoroughly a particular block by recording precisely its modes and (6) to analyse current vibration desigo methods in the light of these observations; (c) to reduce the scale of these observations and analysis to a model, so as to permit rapid and economical modifications in form to be investigated and general principles to be deduced; frequencies of oscillation; ( d ) to examine the influence of the subsoil and of piles on block vibrations; and (e) if possible, finally to draw up general recommendations for vibration design of turbo-generator foundations in the future.