Bennington Harmon Road Bridge

Information and Findings From Ohio's Historic Bridge Inventory

Setting/Context

The bridge carries a 1 lane, unimproved road over a stream in a rural area of active farms. Posted 3 tons.

Physical Description

The 1-span, 48'-long, pin-connected Pratt pony truss is supported ashlar abutments. The trusses are traditionally composed with built up box section for the upper chords and inclined end posts and eye bars are used for the lower chords and diagonals. There is extensive impacted rust, and rod helpers have been added at the verticals. The outriggers with built up brackets appear to be original.

Integrity

Cover plate welded to end posts and other welded repairs. Helper verticals rods added. Impacted rust on box sections.

Summary of Significance

The pin connected Pratt pony truss bridge dated stylistically to ca. 1890 is one of 20 examples of the important bridge type in Morrow County with the oldest extant example dating to 1874. Many are undocumented and represent the era of standardization. This example is attributed to the Massillon Bridge Co., who sold many truss bridges to the county. It shares details common to identified examples of the company's bridges. This example has significant deterioration and added material making it one of the less complete Pratt pony truss bridge in the county. Morrow County retains many pin- connected truss bridges largely because of the economic issues associated with there replacement in a largely rural county with no industrial tax base.

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. 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'. Prior to about 1890, a variety of panel point connections (including bolts, cast-iron pieces, and pins), end panel floorbeam connections, and lower chord designs were in widespread use. 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. Post-1885 Pratt trusses show a progression toward less variation in their details such that by 1890 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 eclipsed in the highway bridge market by more rigid, rivet-connected truss designs, particularly the Warren design, but also the Pratt design as well. The transition to riveted field 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, 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 1894 and have documented or attributed builders and dates of construction and/or significant connection or member details. Post-1895 examples are less technologically significant.

Bridge Considered Historic By Survey: No