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Similar mouldings run along the ribs at the distance of 2 feet from thebottom, and thh thickness of metal between them is 1 inch.
At the meeting at the crown the ribs present a section of 2 feet in depth,with a uniform thickness of 4 inches; their ends are rounded into circular arcs,which fit into corresponding sockets in the sides of the casbiron key, hereinafterdescribed.
The ends of the ribs resting on the hearing piers are cast with circular holes,to admit the holts which attach the wrought-iron ties; round these holes the metalis swelled into bosses, 4 inches thick, and the same thickness is continued to thebottom of the ribs, which is slightly rounded.
The ends of the ribs just described rest in chairs, forming part of a cast-ironplate, which extends along the whole length of the piers, which is run with Romancement, and firmly bolted to a course of stone, hereinafter described.
The w r rought-iron ties are attached to the ribs by bolts passing through theholes above-mentioned, and are united in the middle by a connecting link andholts. On this joint, which it encloses in a kind of box, rests the main strut.
It consists of a cast-iron pillar, with fins projecting from the sides; the upperpart is cast hollow, in the form of a rectangular pipe, to admit of a strong bar ofwrought-iron being inserted, and firmly riveted in its place.
'This bar extends through a hole in the key, and by means of a strong threadscrew and nut working against the underside of the key admits of an adjustmentof the length of the strut.
The cast-iron open work, between main ribs and the ties, are shown on thedrawings. The top rests firmly against the bottom of the ribs, and is attached tothem by means of feet projecting at intervals and fastened by wrought-iron wedgesinto corresponding sockets cast on the side of the ribs.
The bottom is cast in the shape of a three-sided box, the top resting on theties, the sides enclosing them ; and the box is completed by pieces of boiler-platebeing screwed on beneath, neatly fitted to the edges of the box and cut to theexact width.
The ties are kept at the proper distance from each other by pieces cast atintervals on the top of the above-mentioned box, and fitting accurately betweenthem.
The meeting-plate consists of a cast-iron plate, extending the whole width ofthe bridge, with the keys of the different ribs cast on it at the proper intervals.
The parts between the keys are strengthened by fins projecting from each
side.