Engineering Wonders of the World
Volume I

THE STORY OF THE FORTH BRIDGE. 329 wide, weighed 44 or 33 tons, as the case might be, and included five layers of plates, one . The inch thick each on Lower Bed-plates. the average- The topmost layer was practically only a rim round the outside. All rivets were counter- sunk and chipped flush with the plates so as to give perfectly smooth surfaces. A couple of layers of canvas saturated with red lead served to prevent any water finding its way in between the carefully levelled top of the pier and the bottom of the bed-plate. The accur- acy of the bolt-work was such that, though plate holes and bolts made an almost tight fit, the plates passed down the bolts without any forcing. Before going further, a few figures concerning the first section of our Facts and Figures. subject — the foun- dations and piers— may be given. The caissons contained THE FIFE TOWER IN COURSE OF CONSTRUCTION. RR, Riveting Cages. 400 tons of steel and 2,300 tons of iron. More than 33,000 cubic yards of excavation were needed for the founda- The Superstructure. tions, which consumed 44,000 cubic yards of concrete, 2,538 yards of brickwork, and 2,625 yards of rubble. Into the piers were built 29,510 cubic yards of rubble, and 135,386 cubic feet of granite, besides 300 odd tons of iron belting and bolts, anchor-plates, etc. These quantities will give some idea of the scale of operations. As the piers and their foundations are for the most part out of sight, it is interesting to notice that the Inch- garvie north-west pier (including caisson) would, if stood on an open field, tower 107 feet into the air. and have a greatest diameter considerably exceeding the length of a cricket pitch. We now come to the steel superstructure based on the twelve main piers. Beginning at the bottom, we encounter first the upper bed-plates, which form the lowest part of the giant skew- Skew- ü t)3.cks ’ 5 backs, from which spring a large number of the main members of the bridge. A matter which exercised the engineers considerably was the need for providing against the effects of wind pressure and changes of temperature upon so huge a struc- ture of steel. To grasp the problem fully, one must bear in mind the fact that the horizontal members of the towers were as