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Evidence of the emergence of an independent cable structure technology in
Texas centers around US Patents issued to three Texas inventors in three
consecutive years; 1887, 1888 and 1889. These wire-based bridge patents have
recently come to light as a result of research by the Historic American
Engineering Record (HAER). HAER historian Dr. Mark Brown has pointed out that
the arrival of the railroads in the 1870s and 1880s increased demand for roads
and bridges in Texas.
Amendments to the state constitution in 1883 and 1890 authorized county
commissioner's courts to levy taxes for road construction. Development of the
wire-based bridge patents can be seen as a response to the demand for economical
bridges in locations remote from railroad infrastructure. The inventors resided
in three contiguous north Texas counties along the Red River border with
Oklahoma: Montague, Cooke, and Grayson Counties. Considering their temporal and
geographic proximity, it is difficult to imagine that the men did not have some
interaction either as partners or as competitors.
Patent of Joseph Mitchell, Montague County (1887)
Joseph Mitchell’s patent was granted August 16, 1887. It depicts the use of
ground anchored, galvanized wire deck cables, what would today be called a
"ribbon" bridge.
The structure also features redundant timber struts and metal rod stays
superimposed on the ribbon system. The struts and stays form cantilever arms
extending from intermediate timber pier posts towards the center span. A
king-post truss suspended between the cantilever arms completes the structure.
Mitchell makes it clear in his patent that he considers the wire deck cables
and his system for post-tensioning them by inserting a rod between the cable
wires and twisting them to be his unique new contributions. No structures
employing Mitchell's patented system are known to exist in Texas. There is
evidence that Mitchell left Texas in 1888 and continued his career building
bridges in Indiana.
Patents of Edwin E. Runyon, Cooke County (1888 – 1893)
E. E. Runyon was granted six bridge patents from 1888 to 1893. His first,
granted December 18, 1888, the year Mitchell departed Texas, depicts a structure
with striking similarities to Mitchell’s structural system. It has
ground-anchored deck cables "formed of continuous twisted wires" and draped over
intermediate piers, as shown below.
Runyon's piers are of the same configuration as Mitchell's piers except they
are made from "tubular metallic braces" rather than timber. Mitchell's redundant
timber struts are eliminated entirely, and his metal stay rods are replaced with
wire cables.
The suspended span is eliminated by the use of a center floorbeam supported
by a continuous cable stay draped over each pier. The result is a rather elegant
cable-stayed "ribbon" bridge.
Runyon’s additional patents focused on various details not shown in the
initial patent. The remnants of two Runyon cable-stayed "ribbon" bridges have
survived. Although little is known about the life of Runyon, the prolific output
of his partner, William Flinn, has saved Runyon from obscurity.
Patents of William H. C. Greer, Grayson County (1889 – 1912)
The third patentee was William Henry Clay Greer. Greer was granted a patent for
a basic suspension bridge in 1889 and a second patent for supplemental details
in 1894. After 16 years, he repeated this pattern with two more patents: a
bridge patent in 1910 and a second for supplemental details in 1912. Greer
claimed that his use of wire rope rather than built-up cables was a labor saving
innovation. A bracing scheme Greer devised to control deflections of
the wire rope catenaries is shown below.
All of Greer's patents are for catenary cable suspension bridges with two
main cables. He makes no use of the deck cables, cable stays, or the twisted
wire characteristic of the Runyon patents. He eschews the use of cables spun in
situ from coiled drawn bridge wire.
The remains of the only known extant Greer structure are on private property
in Grayson County. On this structure, the "independent cables" are wire rope.
The floorbeam connection matches details shown in the earlier pair of Greer
patents.
Greer patents provide details showing his main cables, ground-anchored to a
toggle bar of "tough wood or bar-iron." The patents also indicate that he was
preoccupied with bracing schemes to control the deflection of the catenaries.
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