A 400-foot-long bridge that many Portlanders use without giving a second thought has been added to the National Register of Historic Places based on its importance in the city’s development and its vintage construction method.
The Balch Gulch Bridge, completed in 1905, carries NW
Thurman Street across the gulch between NE 29th and 31st
Avenues. Soon after its completion, the
bridge became a popular and well-publicized viewpoint of the young city during the
1905 Lewis & Clark Exposition.
“The city promoted the streetcar route into Willamette
Heights as a scenic outing for fairgoers, and vantage points accessible only
via the bridge were featured in promotional photographs of the fairgrounds,” historian
Michael Taylor wrote in a comprehensive National Register document. “The
bridge’s role in showcasing Portland’s natural beauty and development potential
helped elevate the city’s image and encourage private investment, while the
improved access to Willamette Heights accelerated the neighborhood’s first and
most intensive phase of residential growth.”
A wooden predecessor built in 1892 was not strong enough to
carry street cars. Until the new bridge
opened, trolley riders had to get off a streetcar, walk across the wooden
bridge and board another car on the opposing side.
The 1905 bridge is composed of two trusses of 160 feet and 60 feet in length, sitting on three steel towers atop concrete bases. The deck of the bridge sits on top of the triangular truss structures.
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| Drawing shows span trusses and towers |
Unlike modern bridge construction, the trusses were held
together by pins – essentially large threaded bolts. The pin system allowed for speedy erection
and for some modest joint movement, based on load stresses. As historian Taylor notes, pins in newer
construction have been replaced by rivets that are considered stronger and less
susceptible to wear.
Taylor wrote that pin construction “reflects the dominant
connection method for truss bridges erected in the late nineteenth and very
early twentieth centuries. By the early 1910s, most new bridges employed
riveted joints, and over time Oregon’s inventory of pin-connected bridges has
declined.”
The Balch Gulch Bridge underwent renovation s in the 1920s,
the 1950s and again in 2014. The 2014
work paid close attention to keeping or restoring original visual elements of
the bridge, including reconstruction of decorative railings on the sides to match
the originals removed in 1955. The 2014
work also added new steel planks as the decking material.
“Despite these alterations, the bridge maintains nearly all
its character-defining features, including its Pratt deck truss design, pin
connections, original steel trusses and towers with concrete footings, and
location spanning Balch Gulch in northwest Portland’s Willamette Heights
Addition,” Taylor wrote. “It therefore
retains integrity.”
------ Fred Leeson
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