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clearance, which was 14'-0" and 12'-0" less than the bridge's height. After supporting the bridge under the floor beams, they disassembled the top chord and stabilized each panel point on the trusses. [151]

Steering the bridge under the Manchester Bridge and the railroad bridge at Brunot's Island, the tugboat captains went through the Ohio River lock and up the back channel toward Coraopolis, where piers and abutments had been constructed. Reversing the process and using the same jacks and steel frames to raise the structure 32'-0", the company erected the Cooper bridge 30 days after the project began. [152]


Completing the Sixth Street Bridge

Work proceeded on the new Sixth Street Bridge, with the Foundation Company called to accept last-minute revisions of piers 1 and 4 to accommodate subway construction at a later date. Bion J. Arnold's influential transportation report called for converting street-level areas downtown to pedestrian and automobile use. He recommended building tunnels for subways to connect Pittsburgh's central business district with selected areas, including the North Side. Although business owners and city officials hotly contested the exact route for such a system, the North Side access required by any future subway system was not in doubt. [153]

The revisions proposed constructing tunnel shields that could be pierced when the city decided on a final route. The tubes were 68'-0" on center, with suggested radii ranging from 7'-9" to 9'-0", and steel reinforcement overhead. One proposal for the construction shows plans using three separate open box caissons to form the base of each pier. [154] The tube openings provided slightly different angles for each direction to adapt to the grades and length of approaches on north and south shores, anticipating lines that bent outward to avoid the two main piers. The city of Pittsburgh absorbed the cost of the alterations to the original plan, paying the Foundation Company the same contract costs negotiated for the bridge work of up to $40,000 for the south pier and $80,000 for the north pier. [155] (The subway openings have yet to be used, however. Pittsburgh's underground light rail system, constructed between 1980 and 1985, follows a Sixth Street alignment for several blocks but does not cross the river.)

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[151] ACDPW, "Floating Intact."

[152] ACDPW, "Floating Intact."

[153] Arnold, Report.

[154] "Scheme B, Suggested Plan for Using Three Separate Open Box Caissons for Base of Each Pier," 23 Aug. 1926, in Files AL 02-04, ACDPW.

[155] City of Pittsburgh, to Allegheny County, regarding articles of agreement for construction work on the south pier and abutment of the Sixth Street Bridge and the north pier and abutment of the Sixth Street Bridge, in File AL 02, ACDPW. See also Drawings No. 287 and 297 (23 Nov. 1926), in Files AL 02-04, ACDPW.




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Even with the subway alterations, the Foundation Company completed its work four months ahead of schedule, leaving to the American Bridge Company a working schedule during Pittsburgh's bitter winter weather. The company continued to fabricate components at its Ambridge shop, completing two-fifths of the 6,000 tons needed while it waited for better river conditions. In the meantime, workers pre-assembled smaller components off site. Brown's office justified the apparent delay in a press release, responding to business owners who insisted that work continue amidst the winter by noting no contractor could reasonably be expected to erect the side-span falsework necessary for the project with the dangerous currents and ice faced by the American Bridge Company. The uniqueness of a suspension bridge erected by cantilever methods required exceptional caution. [156]


Conclusion

Its predecessor razed in September 1924, the Seventh Street Bridge was the first completed. The county opened the Seventh Street Bridge on 17 June 1926, and the Ninth Street Bridge on 26 November of the same year. County commissioners soothed area business owners anxious for a return to normal commerce by allowing pedestrians to use the Sixth Street Bridge's downstream sidewalk on 14 September 1928, in advance of the bridge's official opening. In a move that symbolized commitment to keeping its public works promises, the capstone of Allegheny County's 1924 construction program was brought to a close almost exactly four years after workers began tearing down the first of the three bridges. The Sixth Street Bridge was opened to all traffic on 19 October 1928. [157]

The county's public works projects in the 1920s employed local labor instead of contracting with outside consultants or companies, and materials were procured from area manufacturers. "Every pound of the thousands of tons of steel used in our bridges was manufactured in the mills of our district," Armstrong wrote in his re-election campaign literature in 1931. He reminded voters that he had helped oversee the construction of ninety-nine bridge projects at a cost of $47.2 million Included in the list were the Coraopolis Bridge, at Neville Island in Coraopolis Borough in 1928, costing $0.8 million; the Sixth Street Bridge in 1928, $1.5 million; the Seventh Street Bridge in 1926, $1.4 million; and the Ninth Street Bridge in 1926, also $1.4 million. Significant in themselves, the bridges were only part of a massive $31 million construction plan beginning in 1924 and ending in 1931. Armstrong boasted, "More county

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[156] Carbon copy of memo,"New 6th Street Bridge," n.d., in File AL 02, ACDPW.

[157] Plowden, Bridges, 239; "Ninth St. Bridge Formally Opened," Pittsburgh Chronicle Telegraph, 26 Nov. 1926, in Clippings File, Pittsburgh Bridges -- Ninth Street, Pennsylvania Room, Carnegie Library, Pittsburgh, Pa.; "Parade Marks Sixth Street Span Opening," Pittsburgh Post-Gazette, 20 Oct. 1928, in Clippings File, Pittsburgh Bridges -- Sixth Street, Pennsylvania Room, Carnegie Library, Pittsburgh, Pa.; and "Opening of the Sixth Street Bridge Sidewalk, Friday, September 14, 1928, 4:00 P.M. Daylight Saving Time," press release from Norman F. Brown's office (12 Sep. 1928), in File AL 02, ACDPW.




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improvements were made during this 8 year period than during the previous 136 years of the county's existence. [158]

One of Armstrong's pieces of campaign literature, a lavishly illustrated brochure, prominently featured an aerial view of the "Trinity of Bridges" overlaid with a photo of American Institute of Steel Construction's 1928 award to the Sixth Street Bridge. [159] AISC named the structure "The Most Beautiful Steel Bridge" constructed in 1928, adding to the fame of the Allegheny County Department of Public Works and publicizing the potential of steel for enhancing not only strength but attractiveness One of five judges, Charles Evan Fowler, commented on the choice of winners:

The new Sixth Street Bridge at Pittsburgh was selected because in my opinion it combined the essential elements of beauty, simplicity, symmetry, harmony, and proportion, and also because of its originality of design, it being a self anchoring eye-bar cable suspension bridge. The cables have enough section to give a very satisfying appearance of stability, combined with simplicity of construction. The towers are very chaste in design, yet heavy enough to give every appearance of strength and solidity. The large arch over the roadway is surmounted by an unequal number of portal openings, yet very harmonious with the entire design of the towers, and the graceful curve of the cables. [160]

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Last modified: 05-May-2003

HAER Text: Haven Hawley, August 1998; Pennsylvania Historic Bridges Recording Project - II
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