McMillan Street Bridge

Information and Findings From Ohio's Historic Bridge Inventory

Setting/Context

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.

Physical Description

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.

Integrity

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 Company.

Justification

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