Fig. 130.—Elevated Foot-bridge.
The posts and top rails are 4½ in. or 5½ in. in diameter, and the intermediate rails 3 in. in diameter. [Fig. 126] indicates the method of jointing the rails to the posts. The girder spars, with posts and rails fitted, having been placed in position on the sleepers, and plumbed up and stayed, the floor battens, 11 in. by 2½ in., are fixed and the struts are fitted and pinned or spiked to the posts and sleepers. The joint for the struts is shown by [Figs. 127] and [128].
Fig. 131.—Girder and Post of Elevated Foot-bridge Bolted to Sleeper.
Fig. 132.—Cross Section of Elevated Foot-bridge at Lower Step ([Fig. 130]).
If the bridge happens to be in a locality that is subject to periodical flooding, it should be anchored to prevent its being unseated by flood water. The anchoring can be best effected by driving four short piles into the soil on the inside of both girders and near their ends. The girders can be fastened to the piles with coach bolts. The tops of the piles will be concealed by the end floor battens. The smaller twigs forming the ornamentation are now fixed, and [Fig. 129] shows the vertical piece hollowed to fit the rails.
[Fig. 130] gives a part view, in longitudinal section, of an elevated bridge, suitable for a span of 12 ft. to 18 ft., and raised on piles to enable small boats and canoes to pass under. Elm logs are suitable for the pile foundation. An iron ring must be fitted over the tops of the logs while they are being driven, and it will be necessary to use a pile-driver. The logs, having been sufficiently driven, are cut off to the required height from the ground line. Three piles on each side are required to carry the sleepers. The bridge is 5 ft. 6 in. wide, and the spars for girders are 12 in. in diameter. The sleepers are bolted to the piles, and the girders are also bolted to the sleepers as shown by [Fig. 131]. A row of smaller piles is now driven, and a plank, 11 in. by 3 in., is housed to the top ends of these piles, and also connected to the projecting ends of the girders. The treads of the steps rest upon the tops of the smaller piles, and the outer side of the piles and planks is covered with split saplings (see [Fig. 130], and the cross-section, [Fig. 132]). The handrails and balustrades are fixed in similar manner to those in [Fig. 121].