The Viaduct Works' Handbook

43 = £12,000 55,640 Therefore 1800 feet, at £7 10s. per foot This would necessitate the use of 26 piers as before each 200 feet high, which, at the same price would amount to ....................... The total cost being . £67,640 From the above it will be seen that where piers of great height are necessary, large spans are most economical. On the other hand, if their height is small, it will be found that small spans and nu- merous piers are more economical than large spans and few piers, because, in the latter case, the cost of the spans will be much greater in proportion to the space covered, and the quantity of material in the piers must also be increased in proportion to the greater weight to be carried by them. The piers of Crumlin Viaduct combine, with lightness and strength, economy of material and facility for erection. A description of one of the highest will apply to all, as they only differ in height. It consist of fourteen hollow cast-iron columns, 12 inches external diameter, arranged in the form of an irregular hexagon, as shown in plan, Fig. 1. The two columns aa are of metal 1 inch thick, all the others are -inch thick; each column is 170 feet long, consisting of ten lengths, each 17 feet, connected by bolts passing through lugs cast on outside, as shown at Figs. 4, 5; a projection of ± inch is formed on one end of each, which fits into a corresponding recess inside the adjoining length; all are accurately turned and fitted at the joints; the bottom rests on a short piece of column jointed in similar manner, and formed into a base-plate 3 feet square, and is 2 feet 3 inches high ; strong 1-inch feathers cast outside to distribute the pressure of column upon the base-plate. The base-plate is fastened to the masonry or rock by ragbolts 12 inches long, let into the stone, and secured there by pouring in the interstices molten brimstone. The top or head of each column is formed into a cap 2 feet square, 1 inch thick. The columns are all connected together by a system of horizontal bracing, which occurs near each joint, or at the top of each length, or tier, of columns, and consists of cast-iron distance pieces, of a girder form of section, with a flange running through its centre, called “distance girders;” they are 12 inches deep, 5 inches wide, and 4- inch metal, arranged as shown in Fig. 2; the columns are formed