The Ashburton Guardian, COUNTY AGRICULTURAL & SPORTING RECORDER. SATURDAY, JANUARY 3, 1880.
The collapse of the great bridge across the Tay at Dundee cannot fail to cause much consternation in engineering circles, as well as amongst the travelling public. The fall of this bridge turns what has been admired as a great engineering triumph into an engineering failure, and the accident will probably have the effect of checking for a time enterprise in the direction of spanning large tracts of water with colossal viaducts. The completion of the Tay Bridge, and its apparent success as a railway track over a wide arm of the sea, had the effect of giving impetus to even a larger undertaking of the same description, namely, a bridge over the Firth of Forth. Last accounts inform us that preparations were being made for commencing the Forth Bridge, and its successful erection would have placed London within a working-day’s ride of the extreme north of railway-reached Scotland. The check given to the Forth Bridge, however, will only be temporary ; for it is a reasonable deduction that if engineering skill can span a great river with a bridge that will withstand the force of wind and current for two years, and then only partly succumb to a fearful gale, the same skill, on finding out the weak point of the first structure, will be able to replace it with one whose added strength will sustain for twenty years or longer shocks of greater severity than that which ruined its predecessor. The loss of life by the fall of, the Tay Bridge, however much to be deplored, is only history repeating itself. In all great en- • gineering undertakings, in a line different and more extensive than formerly known, martyrs have been made to the cause of science, and the human race has had to pay in lives a heavy penalty for learning where errors have have been made, and .how to rectify them. The bridge just destroyed was the largest ever undertaken in any part of the known uorld, and before it was opened for traffic the most severe test the best skill could devise was applied to it, and the result seemed satisfactory to the best practical eyes, ere human life was entrusted upon its huge, though seemingly delicate piers. Whatever of culpability or recklessness may have existed in connection with the building of the bridge or with its working as a part of a railway system, will assuredly be dragged to light, and whoever is to biamo—whether engineer, contractor, railway manager, or workman —for tho loss of 90 human lives,will be held answerable. Still, even the forfeiture of a hundred culpable lives who may, directly or jidirectly, innocently or guiltily, have caused the deaths of those 90 innocent travellers will not again restore the
dead io the world they, have left for tTer. Their part in time is played, and their untimely end is to be deplored, but they leave to those behind a valuable legacy—an opportunity, when all the skill of the scientific world is centred upon one object, of profiting for the future by the lesson their fatal engulphment in the waters of the Tay leaves open to be learned. While we cannot but deplore on the one hand the sad calamity—we would be inhuman otherwise—we cannot shut our eyes on the other to the fact that the terrible accident has been ruled by an allwise # Providence to happen at an opportune time—at a time when the scientific world was big with great viaduct enterprises, over not simply rivers of ordinary force, and over whose waters gales of great force sometimes blow, but actually when it is contemplated to bridge the English Channel, and connect the coasts of England and France with a structure similar in character to that which has given way with such fatal consequences midway between the Scotch counties of Fife and Forfar.
As we have said, the time is big with lessons of living moment to the travelling public, and it is to be hoped the contributions to engineering knowledge given by the weak point of the Tay Bridge will be such as will in a large measure secure travellers in the future who may cross the new structures —when these have been completed, and they assuredly will become an accomplished fact—against unwarned death by a failure of the railway roadway midsea.
It may be well to give a few figures showing the magnitude of the structure whose partial destruction has had such a fatal effect. One of the chief railway companies in Scotland is the North British, and finding that a great detour could be avoided between Dundee and Edinburgh by spanning the Tay at the latter town, the idea of the present bridge was conceived in 1860 by Mr. T. Bouch, engineer. For some years Mr. Bouch’s mind had been directed to the idea of a Tay bridge, and at almost every meeting of the North British shareholders the proposal cropped up—now ridiculed, now approved to some extent. Ultimately the imperative necessity of making the line to Edinburgh from Dundee direct instead of circuitous, and thus bringing more equal competition into play with the Caledonian Company for the direct English traffic with the extreme north of Scotland, became apparent; and Mr. Bouch, having perfected the plan of the bridge that has just suffered, the design was accepted in 1870, the estimated cost being something like £360,000. A tender by Mr. Grote, the contractor who built the bridge, was accepted, at a figure somewhat under the estimated cost, and the the work was proceeded with. It took between six and seven years to complete, but its completion had the effect of hugely increasing the traffic on the line of the company that promoted it. The bridge took the Frith of Tay water at the Magdalen Green, about a mile and a half from the centre of the town, and, following an oblique direction towards the southern shore, struck the Fife side near the hamlet of Woodhaven, half a mile further up stream. The exact length of the bridge over water was two miles, but a quarter of mile of approach was required on either side, and its great length gave it the credit of being the longest bridge in the world. In all, the structure crossed the estuary in 84 spans, the first 14 of which from the Magdalen Green were founded on rock. Six of these were 2i ft long, one 155 ft (to meet rock foundations, and to avoid sand) and seven of COft; another eighteen of 60ft followed ; then eleven of 120 ft; one of 150 ft, and thirteen huge leaps of 230 ft ; from these the spans gradually shortened, from twelve of 136 ft to ten of 120 f t; and then came two of 80ft ; till the southern approach was met in three spans of 60ft. At the Woodhaven, or southern end, the piers were of brick, built on shore and floated out to their position in the river. The remainder of the piers were iron cylinders solidified with concrete, and sunk in the bed of the stream. These cylinders formed pedestals for the supffcrt*t-o|loin. wrought iron pillars on which the'-roadway structure rested, half a mile of which -appears to have given way in the night and caused the accident. The townspeople of Perth raised objections to tbe bridge, inasmuch as it would interfere with the passage of ships up to their wharf. To quash this objection it was necessary to build the structure at an altitude sufficient to admit vessels of heavy tonnage to sail under, and if our memory serves us fairly, the span over the deepest current was 80 or 90 feet high. The writer, however, sailed under a side span in a steamer as large and with as lofty masts as any in the New Zealand trade, and this before the larger spans wore built. The roadway was wide enough to admit of a second line of rails being laid down, but it was deemed advisable, for safer working, to lay only oneThe structure as it spanned the wide estuary had a most fragile appearance in the distance, but notwithstanding its appearance of lightness it took 8200 tons of iron in its construction, 87,000 cubic feet of timber, 15,000 casks of cement, and 10,000,000 bricks, and it was considered so great an undei'taking as to be worthy of a hand-book of no mean size, being devoted to details of its history, and a scientific description of the work of its erection.
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