Issue 1

To the Editor of The Structural Engineer. Water-Cement Ratio. Sir,-In reference to Mr. C S Gray’s letter,Professor Duff A Abrams states that "Aggregates of equivalent concrete making qualities may be produced by an indefinite number of different gradings of a given material." "Aggregates of equivalent concrete qualities may be produced from materials of widely different size and grading." "In general, fine and coarse aggregates of widely different size or grading can be combined in such a manner as to produce similar results in concrete." The meaning seems to point clearly to the fact that size or grading may vary widely in each aggregate, but not the different aggregates unless they have equivalent concrete qualities. W D Williams

We very much regret that the following printers' errors occurred in the December issue of The Structural Engineer :- Page 398- "Stewart & Partridges,Limited" should read "Stewart & Partners, Limited" Page 404- The figure "330 O.D." should read "300 O.D." Page 409-"Chief Surveyor" should read "Chief Quantity Surveyor" Page 42-"Breaking of cracks" should read "Breathing of Cracks".

Perhaps the most characteristic property of metals at high temperatures is their ability to flow or creep when under prolonged load, and it is because of that property that the stress necessary to cause fracture of a metal at high temperatures depends on its time of application. Table I illustrates the marked falling away in the stress required to cause fracture, the longer the stress is applied. In the case of nickel-chromium steel at 600°C and brass at 250ºC stresses less than one fortieth of the breaking strengths determined from ordinary tensile tests at 600°C and 250ºC respectively, cause creep of the order of 10-5 inch per inch per day. If, at the stresses given in the last column of Table I, the creep were continuous at 10-5 inch per inch per day a deformation of 1 inch in 100 inches would be produced in 1,000 days, or roughly three years. In many instances, therefore, even such low stresses as those cited are too high for working stresses. H J Tapsell

Dr Oscar Faber said the paper hardly lent itself to discussion in the ordinary manner, because it was such an excellent description of modern cement manufacture,and nobody could argue with anything that was said in the paper. That made it more difficult to arouse at any rate a very fierce discussion. The first years of his own college course were spent in a cement works, and he had been interested in cement ever since, and for that reason he had appreciated the paper very much. In referring to the universal practice of adding gypsum to make cement slow setting, the author said this is added to the extent of anywhere between 2 per cent, and 3 per cent., but the British Standard specification required that it should not exceed 2.75 per cent. This obviously meant that there was some objection to gypsum if it were introduced in excessive quantities. The objection to gypsum was that an excess of it made a cement what was known as unsound, and it gave the cement certain properties which were deleterious to a permanent concrete.

The future will always hold interest for those who are full of vigour and enterprise and, as a comparatively young and very progressive Institution, we are looking forward with an intense interest to the future and the possible developments in Structural Engineering. It is not intended to put forward any attempt at a prophecy, but rather to indicate in some manner the developments which are at present in their infancy, and search among these for guidance as to the direction in which some headway is likely to be made in the near future. A Lakeman

It has been felt for a long time by those with much practical experience that the statutory requirements governing the employment of structural steel in buildings were quite unnecessarily onerous and tended to produce structures unnecessarily expensive, in which the economic benefit to be derived from the proper employment of constructional steel was to a large extent lost. Consulting engineers in particular have been in revolt against this attitude for many years, and have been firmly convinced that a lower standard of strength, i.e., smaller floor loads and higher stresses ought to be permitted. This view was also taken by the Steelwork Association, who took the long view that if steel buildings could be really economically designed with limitations imposed only by physical requirements and not by indefensible statutory requirements, it would in-the long run benefit industry from every angle. In conformity with this general idea of cheapening building with steel and doing whatever research was necessary to define authoritatively the proper standard in regard to all matters in connection with its employment, the Committee of Council, after con- sulting the Institution of Civil Engineers,arranged for the Department of Scientific and Industrial Research to arrange for this scheme of co-operative investigations.

The designers and manufacturers of steelwork for buildings have expressed continuously, for several years, their view that it is possible to economise to a considerable extent, and with safety, if building regulations would permit. This urge for economy has not arisen suddenly,and has no relation to an economic crisis; the urge arises from a realisation that steel can be utilised to better advantage, particularly in pillars, because greater stresses are justifiable than are at present permitted. The experience of other countries and their development of the more economical and advantageous employment of steel has been noted by British engineers. They have shown that, given less restrictions, they are capable of competing for overseas trade, but they are just as eager to utilise their steel in the most economical way in the home market. It is unquestionably the opinion of a large body of structural engineers that existing regulations are in many respects of a very conservative character and will bear rather drastic revision under several heads. F E Drury

The President, proposing a very hearty vote of thanks to Mr. Creswell for having put the matter so clearly before the members, said he was wondering when structural engineers would have the opportunity to acquire legal knowledge in addition to all the scientific knowledge they must possess; perhaps the matter was one which might be placed before the Institution’s Board of Examiners. Mr W.C.Cocking(Past Member of Council) paid a tribute to Mr. Creswell in respect of his very happy knack of drawing the attention of professional men to various matters, often of very great importance, but which had previously escaped their attention, and said that the paper referred to many matters which professional men did not often consider.