The Viaduct Works' Handbook

44 octagonal at this part, so as to present a flat surface, to which the distance girders are secured by bolts passing through the columns. The distance girders are tied together diagonally by 14-inch round wrought-iron bars, eight in each tier, and in the same horizontal plane, and are marked cccc in Fig. 1; they are secured inside the columns with keys or cotters. The distance girders, connecting the bases of columns, are of larger dimensions,—namely, 18 inches deep, 6 inches wide, and of thicker metal. Between each of the columns there are two vertical wrought-iron bracings, 4 inches wide, | inch thick, marked dd. Fig. 2, or seventy- two bars in a tier, each of which are fastened by a pin at each end, of 11-inch diameter, which connects it to the distance girder, in which pockets of suitable form and dimensions are cast to receive the ends of bars. Each bracing bar is connected with the distance girders at one end by two short pieces of the same size bar,—namely, about 18 inches long, in which an elongated hole, 3 inches by 1 inch, is formed, corresponding to a similar hole in the bracing bar; the latter is secured between the two short pieces by a gib and cotter, which can be tightened so as to adjust the length of the bar to suit the work. The triangles shown by Figs. 6, 7, at ee, surmount each of the piers, and rest upon the caps formed on top length of columns, to distribute the pressure of the superstructure evenly over the whole of the columns; each set consists of a strong cast-iron framing, com- posed of three longitudinal girders 2 feet deep, and eight transverse ditto binding the heads of the columns together, and forming a base, upon which are fixed cast-iron triangular framing pieces, 14 feet high, of suitable form and section to receive the main girders, which carry the floor, and take their bearing only at the apex of each triangle. Four triangles, forming a set, are united by wrought-iron vertical bracing bars, 4 inches by 1 inch, in the manner shown at //, Fig. 7. It will be seen that only two out of the fourteen columns of each pier are placed vertical; all the others are inclined inwards, the greatest inclination being about 1 in 12. In constructing the piers it was necessary to make arrangement by which the main girders could be lifted at the centre; therefore the piers were built to the requisite height without the distance girders marked b, Fig. 1, leaving a parallel opening 5 feet in width