Chai'. XXIII.
136S
jecting parts of the transverse beams, which are mortised on to the piles, and thus be firmlysupported.
Foot Bridge over the Clyde at Glasgno. — The nine bays are carried on pairs of piles,distant about 42 feet apart, and under each longitudinal beam is a second, over theheads of the piles, which extends 10 or 12 feet on each side, and acts as a corbel; thisbeing firmly Ixdted through gives considerable strength to the main timbers, which arefurther strengthened by a truss formed in the parapets of the bridge.
Timber Bridges with longitudinal timbers laid across the stream, and supported atevery 15 or 20 feet by a row of piles driven into the bed of the river, have the cappingplaced upon the heads, and supported by side braces; additional strength is given by
Fig. 2207.
bolts passing through the longitudinal timbers; cross-planking forms the road or foot-way, over the ends of which another longitudinal timber is laid, and iron bolts arepassed through the whole to unite them together.
In narrow foot-bridges the piles may be driven slanting, and united at the top by a cap-ping, which, projecting considerably on each side, serves for the introduction of a strut tostrengthen the side fence or railing.
Fig. 2208.
The piles may be driven further apart when the struts are used to discharge the weightof the platform ; a horizontal timber is bolted from one pile to the other, which servesas an abutment to the struts, and unites the piles which form the piers more firmly.
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