Prospect Mount Vernon Road Bridge

Information and Findings From Ohio's Historic Bridge Inventory

Setting/Context

The bridge carries a 1 lane rural road over a stream in a rural area of active farms and scattered modern houses.

Physical Description

The 1 span, 63'-long, pin-connected Pratt pony truss bridge is supported on ashlar abutments that have been augmented with full-height concrete walls. The truss lines are traditionally composed with no innovative or distinctive details. Cover plate has been welded to some end posts

Integrity

Impact damage. Impacted rust to box section members.

Summary of Significance

The date of construction of the ca. 1892 pin connected Pratt pony truss bridge is not documented in Morrow County records, but stylistically it represents the standardization of design typical of ca. 1890 and later bridges. It 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. Morrow County retains many deteriorating pin connected truss bridges largely because of the economic issues associated with there replacement in a largely rural county with no industrial tax base. This example is not historically or technologically significant.

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-1890 Pratt trusses show a progression toward less variation in their details such that by 1895 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. Post-1895 examples are less technologically significant.

Bridge Considered Historic By Survey: No