Caldwell Road Bridge

Information and Findings From Ohio's Historic Bridge Inventory

Setting/Context

The bridge carries a 1 lane road (closed to traffic) over a stream in a sparsely developed, rural setting.

Physical Description

The 1 span, 114'-long, pin-connected Pratt thru truss bridge is supported on stone abutments. The lightly built bridge has eyebar lower chords and diagonals. The lower chords are guided through the floorbeam hangers in the end panels by a casting with clamps. The upper chords are toe-out channels with lacing on top and battens below. The verticals are channels with lacing. The bridge has A-frame lattice portals. The upper lateral bracing is a shallow, built-up variable depth beam with brackets. It has built-up shaped beams supported from hangers at the lower chord panel points. It is finished with lattice railings.

Integrity

Closed in 1988 due to a crushed floorbeam. The bridge has integrity of design, but materials are deteriorating.

Summary of Significance

The pin-connected Pratt thru truss bridge was reportedly built in 1890 by the Variety Iron Works of Cleveland, according to ODOT's first bridge inventory, although the builders plaque has been lost and the county does not have written documentation. The bridge is technologically significant because of its date of construction and non-standard details, including upper lateral bracing, portal bracing, upper chords, shaped beams, and lower-chord clamps at the floorbeam hangers (Criterion C). This is the only documented example of a bridge built by the Variety Iron Works in the ODOT inventory (July 2009). The Variety Iron Works was established prior to 1879 when a fire destroyed the works. The works were rebuilt and by 1894 it reported a 3,500 ton annual capacity, which had expanded to 10,000 tons by 1903, making it among the six largest bridge works in Ohio. As the company names suggests, however, it did a "variety" of iron and steel fabrication and erection, including buildings, but it was perhaps best known for its dock machinery, including the famous Hulett iron-ore unloaders.

Pratt trusses were undoubtedly the most popular truss design of the last quarter of the 19th century and continued to be built into the 20th century, although eventually superseded in popularity by Warren trusses. The design, which initially was a combination of wood compression and iron tension members, was patented in 1844 by Thomas & Caleb Pratt. The great advantage of the Pratt over other designs was the relative ease of calculating the distribution of stresses. More significantly, it translated well into an all-metal design in lengths of less than 200'. Significant surviving examples of all-metal Pratt trusses mostly date to the last quarter of the 19th century, and they are found with thru, pony, and the less common bedstead configuration. Prior to about 1890, a variety of panel point connections were in widespread use (including bolts, cast-iron pieces, and pins), but engineering opinion was coalescing around pins as the most efficient and constructible. Many of the connection details were proprietary and associated with individual builders or companies, and thus earlier examples are generally taken to be technologically significant in showing the evolution of the design. Later post-1890 Pratt trusses show a progression toward less variation in their details such that by 1900 the design was quite formulaic with few significant differences between the designs of various builders. This marked the end of the pin-connected Pratt's technological evolution and, in fact, it was soon waning and eclipsed in the highway bridge market by more rigid, rivet-connected truss designs, particularly the Warren but also riveted Pratts. The transition to riveted connections, which happened even earlier with railroads than highways, was in no small part due to concerns about stress reversals at the pins under heavier loads and improvements in pneumatic field riveting equipment in the early 1900s. In Ohio, Pratt truss highway bridges, whether pinned or riveted, were almost always built under the auspices of counties and local units of government; the Pratt was not a standard design of the state highway department. There are at least 60 dating prior to 1900 (Phase 1A, 2008). The technologically significant unaltered examples of pin-connected Pratt trusses for the most part date prior to 1900 and have documented or attributed builders and dates of construction and/or significant connection or member details. Later post-1900 examples are less technologically significant.

Justification

Although within well represented population, this example is a rare example of a state fabricator and it is complete.

Bridge Considered Historic By Survey: Yes

View PDF Historic Bridge Inventory Sheet and Historic Bridge Management Plan