I wish to raise two points in connexion with the Paper which presents some much needed data obtained from field measurements. 62.The calculation in Q 46 on the critical percentage of reinforcement must have been made by many engineers but the fact remains that adequate crack distribution can be achieved with lower percentages. The reason may be connected with the fact that plane sections normal to a bar do not remain plane immediately adjacent to it.The stress-raising effect of the bar may, therefore, propagate cracks at lower percentages. This is a problem that might usefully be examined using the dynamic -relaxation technique described in Paper 7033.63.. Secondly, it seems likely that the recommended precautions will not prove to be very practical and the proposal to add ice to the water could be deleterious should some of the ice fail to melt prior to placing. Nevertheless the object of preventing a iemperature rise by heat of hydration is a very desirable one. The following contribute towards this:(U) Avoiding excessively thick sections, in excess of 12 inches.(b) In hot weather, stripping shutters as soon as possible. 65.In fact there appears to be a case for re-examining the CP 20078 requirement for limiting the uncracked concrete stresses. This leads to thick sections with, in some cases, a relatively low percentage of reinforcement. There is a theoretical advantage in having thinner, more heavily reinforced sections. M r 1. B. Aitken, Construction Manager, Jarnes Miller & Partners LtdThe Authors appear to have dismissed the shrinkage characteristics of concrete rather lightly-aggregate shrinkage is very much in vogue and blamed for a number of badly cracked structures. Knowledge, therefore, of the drying shrinkage values of the aggregates used would be of interest.67. The subject in general raises the question of the designer in this connexion and his responsibility. Surely, for a good design of a concrete structure, the designer must accept the deficiencies of the material he will be using and design accordingly, viz. the designer should design the reinforcement to suit his, and only his, positioning of construction joints. He should also position narrow construction gaps (with reinforcement lapped therein.) which, from his own constructional experience, he knows will suit the contractor's method of working. He should then virtually guarantee that what cracks there are will occur at the construction joints and that these, particularly in buildings, will not be detrimental both to appearance and efficiency.68. My overseas experience with cracks, in walls 5-6 ft thick, up to 0.50 mm showed that cracking was eliminated when reinforcement was lapped in contraction gaps and that the temperature rise (35°C) was exactly the same in summer and winter (cf. 0 50) but with a delay of 20 hours in the winter hydration temperature peak.Paper published: Proc. Znsrn ciu. Engrs, 1968,39 (Jan.) 111-125.
said that in paying his tribute to the Authors for the preparation and presentation of their Paper he was very glad that they and their employers were now receiving some of the credit which was due to them for their pioneering effort in designing, building and testing this most successful model of a concrete pressure vessel. He wished to follow the lead of Mr Gill in considering where they went from now, in the situation in which a life sue concrete pressure vessel could be said to be almost "round the corner".121. High standards of integrity would, in any case, be appropriate in the case of a vessel of such large dimensions and important character. Because a nuclear vessel contained radioactivity, the standards should be even higher than might otherwise be acceptable. Vessels of the sort described were novel, there were no accepted codes of practice, and the theoretical evaluation of the strength of such a vessel was difficult and uncertain.122. In his introductory remarks Mr Gill, speaking as a designer, had laid more emphasis upon the testing of the final vessel, but Mr Davidson thought that fundamentally it was most important that the application of acceptable standards should guarantee that the design exhibited a proper margin of safety. That having been done, the testing of the vessel was then no more than a confirmation that this had been achieved.123. As had been mentioned, the factor of safety-to use a well established termcould be assessed in terms either of the ultimate load factor or of the elastic stress behaviour at the working condition. In many ways the ultimate load factor was the more realistic method, but it had its drawbacks, and he did not altogether agree with Mr Gill when he said that it could be satisfactorily calculated in all cases. It might indeed be perhaps not too difficult with a simple barrel, when one considered the hoop loads only, but as soon as one came to consider the closing ends of the cylinder, the evaluation of any theoretical ultimate failing load was extremely difficult; in fact, one was puzzled to know the mode in which it was likely to fail. In this situation one might turn towards the use of model testing, but if so, if one wanted to ascertain the ultimate load capacity of a full scale vessel by testing a model, then that model had to be very much a true to scale model, if only to ensure that it would fail in the same manner as the full scale vessel would. If it were a really true to scale model it might (or might not) be possible to suppose that the gas pressure which caused failure in the model was of the same value as the gas pressure which would cause failure in the full scale vessel. In t Proc. Instn civ. Engrs, vol. 20 (Dec. 1961
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.