Rustic Carpentry :: CHAPTER X. FOOT-BRIDGES.

CHAPTER X. FOOT-BRIDGES.

Very pleasing effects may be produced in public or private recreation grounds by the constructional use of rustic work of good design.

Fig. 121.—Rustic Foot-bridge. Fig. 121.—Rustic Foot-bridge.

Fig. 122. Fig. 122.	Fig. 123. Fig. 123.
	Fig. 124. Fig. 124.
	Fig. 125. Fig. 125.
Fig. 122.—Cross Section of Foot-bridge. Fig. 123.—Enlarged Section of Girders for Foot-bridge. Figs. 124 and 125.—Parts of Joint of Post and Girder.

Fig. 126. Fig. 126.	Fig. 127. Fig. 127.	Fig. 128. Fig. 128.
Fig. 126.—Detail of Middle Rail and Post of Foot-bridge. Figs. 127 and 128.—Joint of Strut to Post of Foot-bridge.

Fig. 129.—Twig Hollowed to fit Rail of Foot-bridge. Fig. 129.—Twig Hollowed to fit Rail of Foot-bridge.

Fig. 121 is a perspective view of a rustic foot-bridge suitable for a span of 8 ft. or 12 ft. The banks of the stream to be bridged are excavated to allow of the building of a low rubble wall, on which the sleepers rest, as shown in Fig. 122. The girders are formed of spruce or larch spars. In the present instance, four are used; and they may be 8 in. or 10 in. in diameter, according to the length of the span. They are roughly adzed down to sit on the sleepers, and each girder is also worked down tolerably flat on the inner sides. The girders are then bolted together in pairs with six ¾ in. diameter coach bolts, as shown by Fig. 123. The posts are tenoned and wedged to fit mortices in the girders. Figs. 124 and 125 show the mortice and tenon joint.

Fig. 130.—Elevated Foot-bridge. 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. 131.—Girder and Post of Elevated Foot-bridge Bolted to Sleeper.

Fig. 132.—Cross Section of Elevated Foot-bridge at Lower Step (Fig. 130). 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.

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