Tay Bridge Disaster Letters 2: ‘The Tay Bridge A Wind-Trap’ (17 January, 1880)

On the 28 December 1879, the Tay Rail Bridge designed by Thomas Bouch collapsed in a terrible storm. The disaster claimed the lives of all 75 passengers (although only 60 bodies were found). Naturally the tragedy featured heavily in ‘The People’s Journal’ and large features on the inquests were regularly found in the paper throughout 1880. Amongst the reporting there were also letters from readers published about the events. In this letter “A.H.” discusses a perceived design flaw in the bridge.

 

“A.H.” writes:—The Tay Bridge was a wind-trap because it was constructed with open lattice work. Those who understand the matter know this; those who do not may think the statement ridiculous. The latter believe, and the engineers who designed the Bridge seem to have believed, that by constructing the sides with open lattice work the wind would pass through without exerting its full powers on the Bridge. Let us examine the facts and illustrate them. Any one who has stood by the side of an exposed wall in a snow-storm and watched the driving snowflakes must have noticed that the current becomes deflected a good distance before reaching the wall, and, instead of striking the wall, as one would at first sight suppose, passes right over. This is what always happens with a wall close from bottom to top. Watch it as it blows towards an open, sparred wall of the same height, and you will see it make straight for the opener fence, which it will strike with great force and will not pass through to the extent one might suppose (just as in the case of the close wall), which it strikes with very much more force than would at first sight appear. From where this is written there are some narrow strips of plantation; one of them is protected by a boarding 5 feet high, and this boarding is close. The other was protected in the same way, but with this important difference, it was composed of sparred work. The spare were nailed on perpendicularly, with two inches between them; they are 4 inches broad. What is the result? Equally exposed, the sparred fence has been utterly demolished. Pieces of it too large for two men to carry were blown twenty, and in one instance forty-five yards. The close one is a little awayed, but has sustained no serious damage. Mark this difference in the way each was secure. The close one was put up carefully, the posts to which it was nailed being of a substantial nature, and they were carefully secured in the ground. Its purpose was to shelter a plantation, and it only incurred the force of the gale at a little distance beyond where it was put. The other was equally well put up, and had the additional support of a very securely fixed stay (buttress) to every post. Those who put it up were acquainted with the above facts as to the manner wind behaves with close and lattice work, and yet it is wholly ruined, while the other stands. While it stood it afforded much better shelter than the close one; it caught the current of wind; the other (close) one deflected it. Another instance:—There is a garden here much exposed, and for the purpose of sheltering it it was surrounded with a wall. Any one acquainted with such knows that it is only the ground within a few feet of the wall that can or will derive benefit from it, while the pent up wind only strikes the ground a few yards on with augmented force. But place, a foot or two off, such a seemingly useless barrier as wire-netting, and the shelter which will be afforded will be such as never so many feet of wall could not afford. Should any one doubt this, don’t sneer; try the experiment. Fancy may say that the comparatively large open space and thin wire of the netting will allow the wind to pass easily, but fact teaches us a very different thing indeed. Fasten a board at the bottom of a stream and provide against the water passing below it; then test the pressure, and you will be surprised at its littleness. Why? The water passes easily over the top. Construct a piece of lattice work of equal dimensions, with spaces equal to the breadth of the spars to allow the water to pass through, and you will find the pressure materially increased. This is exactly the opposite of what one would expect, but it is not our expectation that we must calculate on. But it may be urged that the open spaces of the Tay Bridge lattice-work were as large as to allow the wind to pass easily. This is more apparent than real, and we must never forget that what the first side allowed to pass would be intercepted by the other. A passenger train has the same liability to catch the wind, the spaces between and underneath the carriages acting in the same way as the spaces between the lattice work. Regarding it thus, any one may at once see through the fallacy of the theory which supposes that the train in question withstood the wind when exposed to its full force, and got blown over when partially (at least) sheltered. We might cite any number of witnesses to prove our case. That is not our object. It is to direct attention to facts which, had they had due consideration, might have saved many thousands of pounds, and prevented such a sad loss of life. To point out the best form of girder to present the least resistance possible to the wind would take up your space needlessly, for once the principle is recognised there is no fear of the details being properly planned. Buttressing or cabling may also be left alone, as, doubtless, these will receive due attention May we, however, suggest a combination of both? The pier which supports a buttress may also serve as a hold for cabling. Before closing, allow me to suggest to railway officials the desirableness the sticking in twigs of willows on all places on railway cuttings where springs render landslips possible. Such occur every winter, to the no small trouble of those who have the care of keeping the way clear, and the no small expense of the proprietors and sometimes to the danger of life. Cuttings of willow stuck in before the leaves expand will root and grow, and the roots will bind the whole into one. If desirable, the tops may be cut down yearly after the first year or two without in any way affecting their usefulness. Such an offer issued to each surfaceman would end in a great saving and cost the proprietors nothing, as willow cuttings are to be had anywhere, and these thrive best in wet, spongy places.

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