Blome Road Bridge

Information and Findings From Ohio's Historic Bridge Inventory

Setting/Context

The bridge carries 1 lane of a 2 lane road over a stream in the village of Indian Hill. There are stop signs at either end of the bridge for traffic control. The adjacent quadrants are wooded. A sign on the bridge identifies it as an Indian Hill Historical Society Historic Landmark.

Physical Description

The skewed, 1 span, 94'-long, pin-connected, Pratt thru truss bridge was built in 1888 and underpinned with a steel stringer superstructure in 1990. The truss floorbeams rest atop the stringers. The truss is traditionally composed of built-up compression members and eyebar tension members. The upper chords are toe-out channels with cover plate and battens. The verticals are toe-out channels with lacing. The upper lateral braces are T-shaped sections that connect to the upper chords with U-shaped clips. The bridge has lattice portal bracing. There are two lines of pipe railings that connect to the end post coverplate with cast-iron pieces. U-shaped hangers pick up the built-up floorbeams at the lower panel points. The end panel floorbeam hangers are an unusual detail of threaded rods that pass through a cast-iron separating piece between the lower chord eyebars and are fixed by a plate to the lower flange of the floorbeam. The bridge is supported on stone abutments with concrete extensions to accept the underpinning girders.

Integrity

Underpinned with steel stringers in 1990. Floorbeams have section loss and have been strengthened with welded plate at the webs. Some welded repairs to the inclined end post cover plates at the bearings. The underpinning has relieved the truss of live loads but the truss lines continue to function as trusses.

Summary of Significance

The 1888 pin-connected Pratt thru truss bridge was designed by engineer William H. Harrison and fabricated by the Queen City Bridge Company of Cincinnati. It is an early and complete example of its type/design that reflects the work of a local builder prior to the era of standardization. The bridge has details that are not common to other builders, including the floorbeam hanger detail and the pipe railing detail with cast-iron pieces (Criterion C).

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design of the last quarter of the 19th century and continued to be built into the 20th century, although eventually superseded in popularity by Warren trusses.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. Ohio has three covered bridges that use this combination configuration, but they are all modern reconstructions based on the Pratt patent. 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.

In Ohio, there are 185 Pratt trusses dating from ca. 1874 to 1945 with 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. Significant unaltered examples of riveted-connected Pratt trusses date from ca. 1900 to 1915.

William H. Harrison, the bridge's engineer, was Cincinnati's City Engineer from ca. 1872-1889. He was also for some time the chief engineer of the Queen City Bridge Company, and he located and oversaw the construction of some sections of the Cincinnati & Eastern Railway. He died in April 1889.

Justification

The bridge is one of over 150 extant pin-connected truss bridges dating from 1874 for pony trusses and 1876 for thru trusses. Twenty six predate 1888 and represent the era of experimentation that evolved into standardized designs by about 1888. This example has moderate significance because the genre that is so well represented in Ohio.

Bridge Considered Historic By Survey: Yes