Engineering Wonders of the World
Volume I

336 ENGINEERING WONDERS OF THE WORLD. when the ties should have been cut and the girder allowed to ride free. It was also essen- tial that the plate-ties should be released immediately, to permit the cantilevers to contract when the air cooled. DIAGRAM SHOWING THE JOINING-UP OF A CENTRAL GIRDER BETWEEN CANTILEVERS. ww, Wedges. The Fife girder was taken in hand first. Wedge-pieces to fit the top gaps accurately at a certain temperature were made and drilled ready for bolting. Also, A furnaces were built round the Delicate plate - ties to heat them to Task. redness—and softness—while the riveting-up should be in progress. After several days of waiting the rivet holes in the two ends of the top boom coincided. The wedge-pieces were driven down and made fast, and the furnaces started round the plate-ties. At the critical moment the bolts were knocked out, allowing the girder to ride free on its own bearings as an independent whole. In the case of the Queensferry girder the heating of the ties was not done fast enough, with the result that the sudden change of temperature sheared the last A few bolts, and freed the girder Dramatic with a sudden shock, which Episode. was fe}t from One end of the bridge to the other, and caused a momentary panic. Thus the completion of the bridge-work proper proved somewhat dramatic. The rails of the permanent way are carried in troughs partly filled with transverse blocks of teak and pine set in asphalt, and with longitudinal teak sleepers held in position by wooden wedges. The rails themselves are of the “ bridge ” type, with broad bottom flanges and a longitudinal hollow space underneath, into which enters a tongue on the top side of the fish-plates Ingenious at rail-junctions. Perhaps the Joint most interesting feature of the rail work is the type of expansion joint used at the end of the cantilevers, where a maximum longitudinal movement of two feet is allowed for. At these points the continuity of the rails has to be broken, without depriving the wheels . of support. The difficulty was surmounted in the following manner. From one side of the gap a long rail tongue, cut to a point at an angle of 1 in 63, crosses to the trough on the other side, in which, it rests on a long flat plate. This plate is attached to the end of the other rail, which is bent outwards from the centre line on the same angle of 1 in 63, and overlaps the tongue for a considerable distance. The inside edge of the flange of the rail tongue has long steps cut in it, parallel to the overlapping rail and pressing against studs in the plate attached to that rail. When the gap between canti- lever and girder increases or decreases, the inside edge of the tongue moves parallel to the centre line of the bridge, while the flange pulls the lap rail nearer or allows it to be pushed outwards by the tongue, according to circumstances. In this way the exact gauge is maintained under all conditions. The bridge was opened by the (then) Prince of Wales on March 4, 1890—a memorable occasion in the history of engineering. The total cost of the bridge and its ap- proaches exceeded three million pounds ster- ling. The foundations and piers, with their 140,000 cubic yards of con- crete and masonry, were re- L. S» D, sponsible for £800,000 of this sum. The number of rivets used to hold the 50,000 odd tons of steel together is esti- mated at six millions. But even these figures are perhaps not so striking as the