DiscussionThe chairman, said that with this work, as with all research, what was important was the application of the results in everyday practice. If he had read the Paper aright, it seemed to him that the Author was really advocating that in design one should, calculate on a composite structure, so arranged as to eliminate sway, which meant taking into consideration the infilling or any other factor which contributed towards the stability and strength of a tall frame. In practice, of course, that was extremely diflicult. Many frames were designed without any very clear idea of the details of the infilling. He did not know if that was the fault of architects or of engineers, but it certainly happened in practice, and he was very well aware of it, because as the Engineer to a local authority he was responsible for c h e c k h literally hundreds of structures of the nature in question which were submitted by structural engineers; at the time that they were submitted and had to be approved within a statutory period there were no details of m n g , or at least not s a c i e n t details to make it possible to make proper calculations of the rigidity.65. If the design were so accurate and economic as to have taken note of all the strengthening effects, which in most buildings would be due to infilling rather than bracing, what happened when, as was usual, somebody decided to cut openings in the infilling? Presumably the factor of safety would have to take care of it.66. Crude though the observation might be, therefore, it was important to remember the practical conditions of application, while at the same time acknowledging and being grateful for the very meticulous and careful analysis of the factors themselves in formulating improved methods of design. Dr M. R. Home (Lecturer, Department of Engineering, University of Cambridge) said that there was one point of great practical importance on which he would place much greater emphasis than did the Author, namely, in relation to strain-hardening. In the Author's second example of frame instability, a four-storey frame bent " strong ways", the Author had stated in 8 54: "it is unlikely that strain-hardening occurred except at the centre of the third-storey beam." It was important to remember that the conception of a plastic hinge was an idealization. Unless a hinge formed in a region of uniform bending moment, it never behaved as an ideal hinge and consequently its stiffness did not vanish. This was a direct result of strain-hardening and should be taken into account when dealing with the effect of plastic hinges on stabiIity.68. Fig. 24 showed experimental loadideflexion curves for 8-in. X 4-in. joists submitted to single-and two-point loads. For a two-point load (joist J.3), where between the loads the beam was under a uniform moment, the plastic hinge conception of zero rigidity at the plastic collapse load was almost attained, but under a singlepoint load (joist J.2) the beam retained a rigidity which, although much less than the elastic value, was far from negligib...

said that he wished first to congratulate Mr Alexander on his Paper and on his subject. It seemed to him that the particular subject was very important for the railways and introduced many important items in modernization.62. In the old type of yard with clasp brakes, if the wagon did not conform or the weather conditions changed one had the problem of the wagon stopping short or buffing-up a t too high a speed. The Dowty units solved the problem of varying rollability. 63.The Dowty installation was the latest development in marshalling yards but, of course, all kinds of developments had been going on through the years both in Britain and abroad. He had read most of Mr Alexander's papers and accounts of yards in the United States, Canada, and the United Kingdom and Europe, and there was one item which seemed to him to be most important and yet never seemed to be mentioned. If one followed the processes of a marshalling yard step by step and took these in conjunction with the types of wagon to consider what was the best type of wagon for any process, one reached the rather strange conclusion that the most satisfactory wagon for the purpose was the old-fashioned British standard wagon, i.e. the wagon fitted with loose-link coupling and a hand brake which could be operated by the shunter from either side. 64.Modern wagons had screw couplings and piped brakes, either vacuum or pressure, but in either case the procedure was the same. To undo the brake the man had to step between the wagon and the rails, and he had to do the same for screw coupling. The net effect was that the processing of a series of modern wagons through a yard of this type actually took longer than a series of the older wagons. Also, when the shunter disconnected the pipe at a cut, owing to the requirement that when a train divided by accident the brakes must go on, the mere act of loosening the pipe would put the brakes on, and the shunter still had to exhaust the reservoir before the trucks became mobile. Because of this need, in the case of countries with long trains to which power brakes were fitted, when a train arrived at a marshalling yard the first act of the shunters was to bleed the pipe throughout the train. In some cases this might take about an hour. One therefore had the peculiar anomaly that the most sophisticated yard seemed to be built in order to process the most old-fashioned type of wagon, and it appeared that if one had a modern wagon in that yard it would take longer to process and cause more trouble.65. It would seem that the answer to the problem was an automatic coupling which would operate both the couplings and the brakes simultaneously. The requirements of such a coupling should be as follows :(U) if there was an accidental parting of two halves of a train the brakes must come on immediately ; (b) the shunter must be able to pull a lever which would automatically release the coupling and the pipe, and also operate the valve so that the brakes would not be thrown on, after which the cuts could be humped;

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