Seven Hills Road Bridge

Information and Findings From Ohio's Historic Bridge Inventory

Setting/Context

The bridge carries a 2 lane road over a railroad track and bike path north of SR 16. The rail line and parallel bike path are carried in a deep rock cut. To the south is a brickyard and quarry of the Bowerston Shale Co. During inspection, a high degree of truck traffic was observed. According to period railroad maps, the rail line spanned by the bridge was established in 1853-55 by the Steubenville & Indiana RR. The line was one in a series of links that eventually were merged into the Pittsburgh, Cincinnati, Chicago & St. Louis RR, which became the Pennsylvania RR's Pan Handle Route, the main line west from Pittsburgh to Columbus and on to Bradford, Oh., where the line split with one branch to Chicago and one to East St. Louis.

Physical Description

The one-span, 85'-long, 10-panel, pin-connected Pratt pony truss bridge is supported on ashlar abutments set atop the rock cut of the railway. The bridge is composed of built-up wrought-iron sections and eyebars but the details and composition are unusual within the study population reflecting heavy construction for its original rail-carrying purpose as well as early thinking about truss design. The upper chord is a complex, built-up shape composed of channels, angles, plate, and what appear to be two bulb-T sections although this is difficult to ascertain from visual inspection since the chord is very thick and the outer sections cover the interior ones. The verticals are built up of toe-out channels with lacing but also feature an unusual long rivet detail joining the channels. The diagonals are paired eyebars with a continuous ribbon of shaped bar lacing. The lacing is held to the eyebars by long rivets that pass through both eyebars and the lacing. The lacing also has a short rivet where the ribbons intersect. The lower chords are composed of six eyebars in each panel. The floorbeams are inverted, pin-connected, queen-post trusses with eyebars for the tension members and a rolled section for the compression member. The floorbeams are closely spaced and set directly atop the lower chords. Every fifth floorbeam extends several feet outside the truss lines to form a connection point for a built-up outrigger that is bolt connected to the lower flanges of the upper chord with a shaped, angle-clip detail.

Integrity

The bridge was clearly originally designed as a double-track railroad facility. The date of its relocation as an overpass is undocumented by available records, but it was probably in the early 20th century when the Pennsylvania RR undertook extensive programs to upgrade its lines. Despite relocation, the bridge is remarkably complete. There is some corrosion and section loss in select members, but it has not adversely impacted the overall historic integrity of the materials.

Summary of Significance

The Seven Hills Road bridge is a rare survival of the post-Civil War railroad era of innovation and development in metal-truss design. Its technological significance is exceptional since it could easily be the only railroad pony truss bridge originally designed for double-track, likely main line, service left in the country from this era (Criterion C). There are no similar bridges with these details, especially the upper chord section and floorbeams, that are known to the historic bridge inventory team. The two decades after the Civil War from 1865 to 1885 were when America's railroads rapidly expanded and constantly innovated in developing improved infrastructure and equipment for heavier loads and faster service. This was reflected in the transition from cast-iron to all wrought-iron trusses and a variety of methods experimented with for building up the shapes and making the connections. The Pennsylvania RR, which likely originally designed or ordered this bridge, was considered a leading developer of metal-truss bridge technology. The Seven Hills Road bridge reflects this innovative period in all of its details from the unusual method of building up the upper chord (no doubt so heavy because of concern of railroad loads and the double-track width of the bridge) to the method of lacing the diagonals, to the use of pin-connected, inverted queen-post trusses for the floorbeams. The bridge is dated ca. 1875 based on style, details, and materials. Due to the rapidly changing nature of truss bridge design in this era, bridges like this one remained current for less than 20 years. The intensive-level research that would be necessary to comb through scattered and fragmentary railroad company records was not undertaken. 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.

Justification

The ca. 1875 railroad bridge is unique. It has exceptional significance.

Bridge Considered Historic By Survey: Yes