The construction of the Ohl Street Bridge, located on the Greenville Borough-Hempfield Township line, illustrates the planning and construction process of a metal truss bridge.

        As the area’s industrial center, Greenville expanded south in the late nineteenth and early twentieth centuries, and formerly vacant or agricultural land became valued for industrial and residential development. In 1876, E.W. Hodge established the Hodge Manufacturing Company on New Street. Other industries soon joined it. The largest was the Bessemer & Lake Erie Railroad, which established a major rail yard, repair shops, and a roundhouse in South Greenville. Residential neighborhoods sprang up to house the employees of these plants. A footbridge was erected to allow those living on the west side of the Shenango River to reach these facilities.

Map of South Greenville showing the Ohl Street Bridge and nearby industries in 1931.

Map taken from the 1931 Sanborn Map Company Fire Insurance Map of Greenville, Mercer County, Pennsylvania.

        In September 1907, “not less than twenty-four resident taxpayers” of Greenville and Hempfield Township petitioned the Court of Quarter Sessions for a road bridge to replace the footbridge. The six viewers appointed to appraise the crossing agreed that a bridge was necessary and took the somewhat unusual step of recommending details, including type of bridge (single span steel truss), its length (150 ft) and width (40 ft), the need for a sidewalk, and the width of the approach roads leading to the structure. In all likelihood, this indicated that the Mercer County Engineer already knew what type of truss bridge he planned to design. The viewers presented the report to the Grand Jury on October 21, 1907. It was approved two days later. In November, the County Commissioners agreed to pay for the bridge.

        The Commissioners selected the Canton Bridge Company of Canton, Ohio to construct the bridge. The Pratt through truss bridge constructed by the company was two spans rather than one and, at 256 ft, much longer than the viewers recommended. A contract between Mercer County and the Canton Bridge Company carefully detailed erection specifications. Structural steel was to be used throughout, with the exception of cast steel for shoes and bearings and cast iron for decorative elements such as the bridge nameplates, portal cresting, and railing ornaments. The bridge deck was specified as built up arched corrugated steel plates resting on the lower flanges of the steel stringers to be filled and surfaced with concrete. The center section of the deck was to be much heavier than the rest, in order to support a proposed streetcar line that was never built. This also accounts for the bridge’s width.

        The contract also detailed the dead and live loads the bridge had to accommodate; the degree of workmanship with which it must be erected; and even the approved methods by which it must be assembled. Notably, bridge members were to be erected using rivets driven with pneumatic hammers rather than hammered by hand. However, on-site construction specified the use of pinned connections at the panel points, not rivets. Since the bridge was replacing a footbridge, a broad cantilevered sidewalk was built on the north side of the bridge with provisions made for the possible later addition of a second sidewalk on the south side of the bridge.

Ohl Street Bridge details of pinned connections.

Diagrams taken from the Ohl Street Bridge blueprints 1908.

        The Canton Bridge Company completed the Ohl Street Bridge in October 1909. The bridge featured decorative details designed to enhance the bridge’s aesthetic appeal. The portal struts were embellished with quarter round sunburst cresting and spherical finials, and the sidewalk railing was artfully composed of overlapping strips of metal and decorated with rosettes. Inspectors appointed by the court to insure that the bridge was built as designed called the Ohl Street Bridge “first class in every respect.”