ABUTMENTS, PIERS AND RAILINGS.
stone bridge abutmentFig. 280.—End Of A Bridge.
Fig. 280.—End Of A Bridge.
Fig. 280.—End Of A Bridge.
wooden pierFig. 281.—Framed Pier.
Fig. 281.—Framed Pier.
Fig. 281.—Framed Pier.
If the sills of a bridge are laid directly upon the dry walls of an abutment, or upon a heavy plank, the jar of passing teams soon displaces some of the stones, and brings undue strain upon certain portions of the wall. To avoid this, abutments are best made of cut stones, and laid in cement. A wooden bent for the support of the ends of the bridge may be made as shown infigure 280. The whole should be constructed of heavy timber, pinned together. A coat of white lead should cover the interior surface of all joints. The number and position of the posts of the wooden abutment are seen in the engraving. A log should be laid upon the wall atm, to relievethe bridge from the shock of the passing wagons. A center pier should be avoided as much as possible, as it offers serious obstruction in floods, and ice, driftwood and other floating matter become piled against it, seriously imperiling the entire structure.
stone bridge with central pierFig. 282.—Bridge Supported By Piles.
Fig. 282.—Bridge Supported By Piles.
Fig. 282.—Bridge Supported By Piles.
side and end view of bridgeFig. 283. —— Railing Of Bridge. —— Fig. 284.
Fig. 283. —— Railing Of Bridge. —— Fig. 284.
Fig. 283. —— Railing Of Bridge. —— Fig. 284.
But in cases where the length of the bridge is so great as to require one or more piers, they may be constructed on the plan shown infigure 281, or in case the bottom is so soft as to render the mudsill insecure, a line of piles supporting a cross-timber, as infigure 282. A strong, reliable parapet or railing should always be provided. The want of one may be the cause of fatal accidents to persons and horses.Figure 283gives a side view of a good railing, andfigure 284shows the manner of bracing the posts to the ends of the cross-beams. They should be thus braced at every alternate post of the railing. The floor should be double, as shown infigure 285, the lower planks laid diagonally, and the upper layer crosswise.
wooden planksFig. 285.—Plank Floor Of Bridge.
Fig. 285.—Plank Floor Of Bridge.
Fig. 285.—Plank Floor Of Bridge.