1382
THEORY AND PRACTICE OF ENGINEERING.
Book 11.
Bridge over the Delaware , at Trenton , in AVw Jersey , in America , built by Air. Burr, in1804, consists of five arches of different span, and crosses the river where its width is
Fig. 2279.
DELAWARE BRIDGE.
1100 feet. The arches rise from their chord, line, in the proportion of 13 to 100 feet,and they are all segments of circles : there arc in the width of the bridge five parallel
rows of these arches; one traverses the middle, two are placed at a distance of 11 feet, andadmit carriages between them ; the outer are at a further distance of 4 feet 6 inches,forming two carriage and two footways.
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Fig. 2281.
The ribs are cut from planks of white pine from 35 to 50 feet in length, 12 incheswide, and 4 inches thick; these planks are laid close together, the joints being broken, andhaving an equal depth throughout of 3 feet; they are all held firmly together by ironstraps : thus a rib is made as strong as one of whole timber, and, to prevent them from
Fig. 2283.
springing, horizontal tie-beams are introduced, from one pier to the other, connectedby diagonal timbers with the ribs ; these are carried above the spandrills of the arches,which are filled in with diagonal braces ; thus the ribs are so strengthened above and belowthat they cannot easily change their form.