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A Meeting of the Institution was held at Denison House, Vauxhall Bridge Road, London, S.W.l, on Thursday, December 20th, 1923, when a paper on "The Practical Designing of Structural Steelwork Details" was read by Mr. Joseph B. Clarke; after which a vote of thanks was proposed by MR. S. BYLANDER, M.I.Struct.E., in the following terms:-
He said it was very delightful to listen to a paper of this kind, where a thorough study had been made of the subject, both mathematically and practically. He thoroughly agreed with the principle of the paper, that connections should be denoted by the efficiency; but whether or not each individaal connection should be given a number to represent its strength he was not quite so sure about. Personally, he considered that the simplest method, and the method which undoubtedly would be followed in future by good designers, was to have a table giving the efficiency factor for any one group of rivets with a certain eccentricity. Mr. Clarke had called it the “index number,” but he (Mr. Bylander) preferred the term “efficiency factor.” Mr. Clarke had shown a simple formula for arriving at this factor, and, after all, that was the essential part of the paper. It would be agreed that it was a very laborious matter to calculate the actual strength of every group of rivets used for connections, but Mr. Clarke had worked out and given structural engineers a factor which they could use, without this labour of ascertaining the polar moment of inertia, of a group of rivets, and further, of ascertaining the maximum strength, knowing the stress due to twisting. He did not quite understand why Mr. Clarke had selected the graphical method of ascertaining the factor, from the stress due to the loading and the stress due to the twisting. He himself would prefer to adopt the mathematical formula shown on the screen, and he hoped that, Mr. Clarke would, later, add the details of the derivation of his formula. Obviously the formula he had given indicated the solution by a graphical method. It could be expressed equally well under the root sign. Mr. Clarke had made a statement that the vertical and horizontal component of the stress due to twisting was derived from a formula, but he had not stated the derivation of that formula. He had said that it was, of course, important that th6 stress was ascertained for the outermost rivet, but that, said Mr. Bylander, was not necessarily so. It must be the rivet on which the greatest total stress occurred, and not necessarily the rivet which was the greatest distance away from the centre. Then, Mr. Clarke had not drawn attention to two or three conditions which were very essential to the truth of his argument, namely, that certain assumptions had to be made. The assumption that the centre of gravity of the rivet was the point around which the connection would turn in case any movement took place within the elastic limit, was one, it was an assumption which he
quite agreed with, because it was a si
Prof. S. W. Perrott, in opening the discussion, said he would like to suggest that each member taking part would mention his name. As Mr. Clarke was not present to hear the remarks it was essential in dealing with each point in the paper, to do so as clearly as possible in order that the reports sent forward to Mr. Clarke would be as clear as possible. Continuing, he said that this was a paper very suitable for meetings, and one which should be welcomed because matters of this kind were always wanted to deal with. It is in the details that new things can be done with great advantage. The suggestions set out in this paper formed a type of detail which might be of great use to structural engineers. He hoped everyone would contribute to it. The Hon. Secretary then read a written criticism from Mr. Durose which we hope to publish in a later issue.
The essential factors that I have in mind for the purpose of this short article are labour and materials. There are others, including that of need. Space will not, however, permit oi my dealing with this aspect of the question, although I would summarise the views that I have previously and more definitely expressed with reference to it by saying that the need is very great indeed; and although variously estimated there can be no doubt that it is limited in practice only by the availability of our resources in labour, material and finance.
Sir Charles T. Ruthen