This bridge is an extremely rare example of a steel rigid-frame bridge, also noted for its outstanding Art Moderne architectural detailing. A nice report with some additional history was produced by History in Your Own Backyard as shown below.
Information and Findings From Ohio's Historic Bridge
The bridge carries a 4 lane street and sidewalks
over a 4 lane street and sidewalks in an urban setting in Cincinnati.
The setting is a mix of industrial and commercial development dating
from the 1920s to modern. To the north is a municipal park in the
triangular-shaped block formed by intersecting roads. The grade
separation carries McMillan Street (a major east-west arterial road)
over Reading Road (a major north-south arterial road). The bridge was
built in 1937 to replace an 1899 Whipple truss on the same alignment.
The 3 span, 217'-long, steel rigid frame bridge has
built-up variable-depth built-up, riveted girders with integral legs and
cantilevered end spans. The main span is 117' long, and the side spans
are 50' long each. The 4 ribs have angle stiffeners and riveted cover
plates at the haunches where the stresses are greatest in a rigid-frame
design. The legs are stiffened by transverse girders with arched
soffits. There are transverse stiffeners (diaphragms) with oval-shaped
cutouts between the girders, which were designed in the form of
Vierendeel girders. It has a concrete deck. The bridge is elaborately
finished in the Art Moderne-style with balustrades, stepped concrete
pilasters, and oversized pylons that progress in height from the
wingwall corners to the piers. The pylons were designed to support
stylized aluminum luminaries, which have been removed.
The bridge has the aspects of integrity. The
concrete deck was replaced in 1990.
Summary of Significance
The McMillan Street overpass was built in 1937 by
the City of Cincinnati in the Art Moderne-style that was so popular for
civic works during the 1930s. It is the only pre-1961 steel rigid frame
bridge in the ODOT study (June 2009) and ranks as one of the more
significant bridges of its era from both the engineering and aesthetic
points of view (Criterion C).
The basic engineering principles
behind the rigid frame are that the top member and the legs are integral
and the legs perform useful work in supporting the loads. One of the
advantages to the rigid frame type is that it reduces the mass of the
abutments and thus costly work in the ground. It is an economical use of
materials, and it works well in settings with limited vertical
clearance, such as overpasses. Rigid frames are indeterminate
structures, meaning that the stresses are difficult to predict. Accurate
stress analysis relied on post-1930 advances in engineering theory.
Reinforced-concrete rigid frame bridges have an intrinsic, shallow arch
profile because of the material required at the knees where the top and
legs meet and where the stresses (moments) are the greatest (In fact,
it's not uncommon for them to be misidentified as arches by laymen).
Rigid frame bridges were highly valued for their intrinsic aesthetic
qualities and were frequently favored in park and urban settings. Rigid
frame bridges were introduced into the U.S. during the 1920s but most
examples were built of reinforced-concrete not steel, for the obvious
reasons of the effort required to form the frames by riveting, involving
both the fabrication of girders with curved flanges and the haunches
where the legs meet the girders. In the McMillan Street overpass, the
oversized pylons at the piers serve to hide from view the legs and
haunches of the frame, which were probably considered unsightly due to
the stiffeners and mass of rivets. Steel rigid frame bridges, let alone
multiple span ones with cantilevered end spans, were not often attempted
prior to 1950, and this ranks as one of the most aesthetically
successful in the United States. Today, steel rigid frame bridges are
fabricated by welding, which provides greater flexibility in design.
The McMillan Street Bridge was designed by the Cincinnati Department
of Public Works, Division of Highways. Chief engineer was Armin Aren,
with architectural design by Maurice Schulzinger and structural design
by William Ivers. Kerpen Construction Company of Cincinnati was the
general contractor, and the steel was fabricated by the American Bridge
The bridge has a high level of significance because
of its uncommon steel rigid frame design and period aesthetics.
Bridge Considered Historic By Survey: Yes
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