The through truss spans incorporated in the present Coraopolis Bridge were originally erected across the Allegheny River at Sixth Street in Pittsburgh, linking Pittsburgh with the main business thoroughfare of neighboring
Allegheny City. This was the third of four bridges to serve that location, which is considered among Pittsburgh's most important river crossings. The growth of Pittsburgh was strongly influenced by its numerous waterways, and the successful linking of the city with its neighboring communities by means of bridges was a significant factor in the development of its metropolitan identity. Allegheny City was annexed by Pittsburgh in 1907, becoming the city's "North Side".
First Sixth Street Bridge The first bridge to cross the Allegheny at Sixth Street was a six-span, flat-roofed,
covered wooden bridge constructed in 1819. This bridge had a total length of , consisting of four spans, a span, and a span. The design and construction of this bridge have traditionally been attributed to a Mr. Lothrop; it was presumably a
Burr arch truss, like the Ninth (Hand) Street Bridge, another of Lothrop's products. Physical evidence for this assumption survived until the 1890s, when an observer reported that the skewbacks from the wooden arches remained visible in the north abutment.
Second Sixth Street Bridge In 1860, a wire-suspension bridge, designed by
John A. Roebling, replaced the decaying timber structure. This bridge was four spans long, with two main spans, and approach spans measuring each. The bridge was dominated by cast iron towers, each formed by four cast iron columns. Although the Roebling bridge, with its iron superstructure, was generally believed non-flammable, it fell victim to fire on June 19, 1881. The bridge was not destroyed, but its floor system of white pine and white oak was severely damaged. John Harper, president of the
Allegheny Bridge Company, which owned and operated the structure, stated that he believed the fire was the result of "sparks and perhaps flame from the stacks" of passing steamboats igniting bird nests located under the superstructure of the bridge. After heavy electric streetcars were introduced to the bridge in 1890, concern over its functional capacity grew, and in 1891 plans were begun to replace the suspension bridge with one that could better handle the steadily increasing traffic, as well as permit trolleys to cross without reducing their speed.
Third Sixth Street Bridge The third Sixth Street Bridge was designed by the nationally significant engineer
Theodore Cooper (1839–1919). This bridge has been identified as the last surviving structure entirely designed by Cooper, whose involvement extended even to such details as the bridge's handrail, lamps, and fascia. The third Sixth Street Bridge, like most roadway river bridges in the 19th century, was privately built and operated as a
toll crossing. The total cost of construction was $560,000. This cost was underwritten by the Sixth Street Bridge Company and Fidelity Title and Trust Company, successors to the Allegheny Bridge Company, which had received its charter in 1810. When the bridge was opened in 1893, the toll was set at two cents for each man, while women crossed at no charge. Beginning in the late 1890s, Allegheny County and the City of Pittsburgh undertook a systematic program of acquiring the privately owned bridges within their jurisdiction and eliminating their tolls. The Sixth Street Bridge was purchased by Allegheny County in 1911 along with nine other bridges at the combined price of $2,851,000; all ten of these bridges were subsequently declared free. The trusses for the third Sixth Street Bridge were fabricated by the Union Bridge Company. This company had been formed in 1884 by the merging of the Central Bridge Company of Buffalo, New York, and Kellogg and Maurice of Athens, Pennsylvania. The Buffalo plant was closed around 1890, so presumably the trusses were produced in the shops which remained at Athens. The superstructure was erected by the Baird Brothers, John and William, who first advertised in the Pittsburgh and Allegheny City Directory in 1886 as contractors located at Home and Valley Streets. In the 1891 and 1892 editions of the Directory they were listed as bridge builders; their listings no longer appeared by 1900, and by 1911 William Baird had left the construction business and had begun managing a hotel. The Baird Brothers had been involved with numerous bridge projects and companies in the late nineteenth century. William Baird had worked on seven bridges crossing the
Missouri River, the Merchants Bridge across the
Mississippi River at
St. Louis, two bridges crossing the
Ohio River at
Wheeling, West Virginia, the bridge carrying the
Baltimore and Ohio Railroad across the
Susquehanna River, and bridges at
Steubenville, Ohio, and
Poughkeepsie, New York. John Baird had also been involved in the construction of the
Eads Bridge in
St. Louis and the Cairo bridge in
Memphis, and was employed by the McCann Construction Company, the Keystone Bridge Company, and
American Bridge Company. This bridge was also outgrown. While the
Pittsburgh City Council and the Municipal Affairs Committee of the
Pittsburgh Chamber of Commerce argued for the retention and upgrading of the existing bridges, the issue was ultimately decided by the
Department of War, acting under the authority of Section 18 of the Rivers and Harbors Act of March 3, 1890 (30 Stat., 1121–1153). This act empowered the Secretary of War to require the removal or alteration of any bridge which " ... is an unreasonable obstruction to the free navigation . . . on account of insufficient height, width of span, or otherwise". So, unfortunately, the War Department decreed that the numerous bridges over the Allegheny with their differing spacing of piers, main spans, and generally low clearances, were an impediment to navigation, and decreed that all bridges would have to be replaced. Although the decree was discussed in the early 1900s, and first issued in 1917, serious work did not begin till 1924. As part of the
Three Sisters (Pittsburgh) project, the bridges at Sixth, Seventh, and Ninth Streets were to be demolished and replaced. The other two bridges were destroyed and scrapped, but the Cooper Bowstring trusses were moved to Coraopolis and reused. ==Moving the Sixth Street Bridge to Coraopolis==