THE TAX BRIDGE.

Nelson Evening Mail, Volume XV, Issue 7, 8 January 1880, Page 2

THE TAX BRIDGE.

The Post gives the following description of this bridge which was recently the scene of so terrible a disaster: — The Tay river — or estuary — at the point where it is crossed by the famous and fatal bridge, is a little over two miles broad. Kocks, which on the Fife side rise out of the water, and on the Dundee side approach the surface, disappear as the middle of the river is neared, until at length they are found too far below the river-bed to be of much use as foundations for the piers of the bridge. But there is above the rocks a stratum of gravel 18ft. thick, of which an engineering writer remarks, that it is "quite able to bear the weight put upon it, and so serves the purpose for foundations, although not of the same solidity as the firm and enduring rock. Whether this, after all, proved a source of weakness to the strncture has yet to be learned. The bridge itself is of no fewer than 87 spans, supported by 85 piers, the total length being 10,612 ft, or 2 miles and 52ft. Of these 87 spans, 74 are of varying length, ranging from 69 to 170 ft. But over the middle of the river, the navigable channel, there are 13 spans, each 245 ft long, supported by piers so lofty that at the highest tide there is a clear waterway of 88ft perpendicular, which gives abundant space for the steamers and small vessels which ply between Perth and Newburg. There seems no doubt that these were the thirteen spans which are recorded to have given way. Extending as they did over the navigable channel in the middle of the, estuary, thep would be exposed to the full fury of the tempest, which would have had all the more power owing to the enormous unsupported length of each span (245 ft.), and the resistance offered by the passing train. How it came about that all the thirteen spans gave way together has yet to be explained. The bridge underwent the most severe and stringent tests by the Government authorities before it was allowed to be used for public traffic. One consisted in crossing it with six goods engines belonging to the North British Railway. These are the heaviest and most'powerf ul goods engines in the kingdom, each weighing with its tender no less than 7 1 tons, and were built expressly for the exceptionally steep gradients of the Waverley portion of that line. The. six engines weighing in the aggregate 426 tons — more than double the weight of an ordinary train, and four times that of the one which was associated with the disaster — were not only run across the bridge, but were rested for a time on each of the 87 spans, and the deflection was practically inappreciable. This renders the collapse of a structure so severely and sucessfully tested all the more remarkable unless the foun-

dationg, which, as we have, shown, were hot considered alt that could be desired; proved unequal to the continued strain aiid gave way on its being enhanced by the presstire of a furious storm meeting the resistance of the passing train. It is idle, however, to indulge iv mere conjectures, and we must bo content to await the arrival of full explanations by {aail. Proceeding with our account of the ill-fated bridge, we may mention that it was projected by the directors of the North British Railway Company to save a considerable amount of time, distance, expense, and trouble on the journey between Dundee and the Sbuth. It is estimated that they effected a blear saving of at least £40,000 per annum in working expenses through the erection of the bri ige, while gaining many other advantages. The contract was taken in 1871, but unforsseen delays arose, and operations were not actually commenced uutil August," 1875, the contract having been transferred (on the death of Mr be. Bergue; the original contractor) to Messrs Hopkins'; Gillkes, an.d Co., Mr A. Grot he, C.E., (from whose report we glean the present particulars) being the managing engineer. In two years it was completed, and the first train crossed it on 25th September, 1877, although it was not formally opened for traffic until 3 1st May, 1878. Some Of the piers were of brickwork, set in Port land demerit; others were iron cylinders; the lower portion filled with concrete or brickwork. The bridge itself was constructed on the lattice girder principle, its course being a long curve with the convexity to the westward. The girders were raised to their position by hydraulic power at the rate of 20ft per day. Every possible care and forethought seems to have been exercised on this gigantic bridge, and all available modern engineering skill and mechanical appliances brought to bear in its construction. That, nevertheless, it should have collapsed so disastrously, and with consequences so fatal, will tend somewhat to shake the popular faith in the infallibility of modern engineers, whose readiness to undertake the most stupendous works that the human imagination can conceive has grown into what has been well called " a splendid audacity* '*