Author: Edwards, A Trystan
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Edwards, A Trystan
WEe come now to study a branch of the subject which usually presents difficulty and the failure to understand which has been a common cause of accidents in the past; the mattter is of great importance from the point of view of public safety because the so-called shear failures occur suddenly without warning, whereas a failure due to ordinary bending always gives warning by excessive deflection. Ewart S. Andrews
LT. COLONEL J. MITCHELL MONCRIEFF, C.B.E. (vice President) proposed a hearty vote of thanks to Mr. Digby for his extremely interesting and valuable paper. In the course of his remarks he recalled a conversation he had had with the late Sir Benjamin Baker in about 1896 or 1897, when the Central London Tube Railway was being built. Sir Benjamin had said that he had had the greatest difficulty with vibration: he had thought he had got the thing absolutely like a bed, but, when he went to his club some of his friends, who happened to live over the tube, wanted to know why their china was cracking and their pictures falling. That emphasised the great importance of vibration. Col. Moncrieff also recalled that some years ago he had heen concerned with the building of a chimney about 160 ft. high, and on one occasion happened to be on the platform at the top during a high storm. It was a weird experience to feel the chimney suddenly sway to one side, hesitate, and then come back to the other side, and so on. That was another form of vibration, however.
To the Editor of The Structural Engineer. Sir, I have had occasion quite recently, to discuss with the Manager of a small engineering works, the matter of welding mild steel rods and upon asking him "Can you guarantee your weld?" he retorted by asking "Can you guarantee your steel?" Although the steel rods I was about to have welded were of British manufactsure I could not, of course, guarantee them, nor did I think that, there was any particular merit in the question, until I got a rude shock from my friend (who, by the way, comes from Glasgow, and has had a large experience in engineering and workshop practice) when he explained to me his experience at various times, and even within the past few weeks, of the behaviour of mild steel rods. My reference to welding applies to open forge-welding and rods mean rods foreinforced concrete purposes. I have always held the view that a weld, however carefully forged, could not be as strong as an original rolled rod, arguing by analogy, that, a broken limb, however well set, could not equal in efficiency and strength, the unbroken limb. My concern is not with the strength of welds, but, in arguing the merit and de-merits of welds, my friend was able to point out to me the extraordinary behaviour of round mild steel rods when being bent into truss units. Imagine an ordinary truss, some 25 ft. long of 1 in. section, which, after being bent had become slightly distorted, a very frequent happening. The truss was placed upon an anvil and three blows struck with a 14 lb. sledge-hammer. At the third blow, struck at one end of the rod, the bent portion at the other end dropped off. The diagram shows the relative position of the blow, which was merely a moderate one, and the portion of the rod that dropped off. I was shown the piece (12 in. long) that dropped off, and my friend put it through a severe practical test.