Occasional Electronic Publication No. 1 - Society for Industrial ...

Bowstring Configurations
Not all bowstring configurations are trusses. Tied arches and other non-truss configurations are indicated
with a # symbol.
Bowstring truss: A bowstring truss is a truss with an arched upper compression chord and a horizontal
tension bottom chord that connects the ends of the arched chord. Diagonal members in the truss web
help prevent the arched chord from deforming under moving loads placed on the bridge deck, which is
hung from the arch. Some bowstring configurations are “inverted” with a horizontal top chord in
conjunction with a curved tension chord.
Tied arch: A tied arch contains horizontal thrust by a tension member that connects the ends of the
arch. The bridge deck is supported beneath the arch only by vertical hangers. Any tendency for the
arch to deform due to a moving load on the bridge must be solely resisted by the rigidity of the arch.
PATENT CHRONOLOGY
Long, G. W. 1830: All-timber, Howe-type web with a single diagonal in each panel.
Whipple 1841: Iron. Ends of top chord are splayed. Paired verticals. Crossed diagonals.
# Lanergan 1850: Three overlapping bowstring arches. Labeled “truss.”
Guiou 1856: Iron. Web of radial posts, plus full, half, and quarter-span V-pattern braces.
Avery, G. S. 1857: Layered top chord. Web of crossed diagonal struts and rod ties.
# Meigs & Reeves 1857: Radiating ties originating from common mid-span location.
# Moseley 1857: Web of very closely spaced radiating hangers perpendicular to the arch. Labeled “truss.”
Swartz 1857: Supplemental tension rods extend from short towers to mid span.
# Ham 1859: Curved-chord Howe with single diagonal in panels. Three superimposed full-span arches.
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