THREE SISTERS BRIDGES
HAER No. PA-490
(Page 21)

Allegheny County Government and Public Works

Popular mistrust of municipal government resulted in reform candidates being elected just when the bond issues arose, but the men who had promised to clean up city and county government lacked the connections and experience to force the bond issues through. Ironically, a return to the machine politics provided the push needed to convince voters that raising the bridges would benefit all of Pittsburgh's citizens. [87]

In 1924, three new members won elections for positions as city commissioners. Joseph G. Armstrong and E. V. Babcock earned seats as majority party commissioners, and James Houlahan took the seat apportioned by county law for the minority party representative. "Joe Armstrong was one of the old political czars who had spent his life in politics in Allegheny County," noted George S. Richardson, whose invaluable interview memories of the county building program during the 1920s provide insight into the politics and personalities crucial to building the Three Sisters Bridges. What Armstrong lacked in formal education he made up for in drive and decisiveness. [88] Although controversial because of his connections to political patronage and machine politics in Pittsburgh, Armstrong's ambition to leave a lasting mark on the municipality gave impetus to the county's building program. [89]

The three commissioners were a main reason that the 1924 bond issue passed. Even before approval of funds for bridge and road work, they began restructuring county engineering offices, hiring Norman F. Brown to head the new Department of Public Works. Brown promptly brought the engineering- and design-related offices under the umbrella of a centralized public works agency, so that long-term heads of independent offices became leaders of subordinate sections. Vernon R. Covell moved from County Engineer to chief engineer of the Bureau of Bridges, and A. D. Nutter became the chief design engineer. [90]

----

[87] P. M. Farrington, S. J. Fenves, and J. A. Tarr, The Allegheny County Highway and Bridge Program 1924-1932, Report No. R-82-132 (master's thesis, Carnegie-Mellon Univ., 1982), 43. Farrington et al. provide much information about the bridge program during this period, particularly the effect of political maneuvering on the process of proposing designs. The bibliography is helpful for indicating source material, but the lack of footnotes in the text makes tracing citations to original sources difficult.

[88] George S. Richardson, "History of Allegheny County Bridges: An Oral History of the Bridge Construction Program from April 1924 to March 1937 Inclusive," interview by Steven J Fenves, 2, in File 54: File
54: Bridges -- I -- Lists, Collected Descriptions, Pictures, Drawer I, Cabinet IV, Print Collection, James D. van Trump Library, Pittsburgh History and Landmarks Foundation, Pittsburgh, Pa. (hereafter cited as Richardson, "Oral History").

[89] Although Armstrong did indeed appoint political friends to engineering posts, he made sure that the operations of the department were not encumbered by the presence of non-engineering employees. One story Richardson related was that Armstrong gave Brown carte blanche for employment decisions and merely added absentee appointees to the payroll -- an account similar to gossip reported in local newspapers at the time.

[90] Richardson, "Oral History," 2.




THREE SISTERS BRIDGES
HAER No. PA-490
(Page 22)

Initial Bridge Designs

Four formal proposals preceded the self-anchored suspension form finally selected. [91] A 1910 design by F. A. Glafey, former chief designing engineer of the Keystone Bridge Company and of the American Bridge Company, shows a grade of just under 3 percent -- less than half the grade then on Seventh Street Bridge's north approach and slightly less than that on the Sixth Street Bridge. In 1917, Thomas M. Rees, owner of a stern-wheel boat operated on the Allegheny River, publicized the design, which had not been accepted by the War Department engineers or the County Commissioners. Rees' flyer showed a two-humped bridge, higher at its center point, with current and proposed elevations. [92]

A more seriously considered plan originated from within the county engineer's office. A. A. Henderson designed a continuous-traffic lift bridge, proposing to raise the existing bridge during the navigation season with jacks placed on piers. By using the existing bridge, the cost could be minimized, making the plan more attractive. The War Department rejected the jacking scheme, pointing out that a single jack's malfunction would make the entire bridge inoperable. At maximum height, the bridge would have had a 5.7 percent grade, nearly twice the maximum percent the city wanted. On other hand, for nearly half of the year the structure's grade would be only 1.5 percent. [93]

In order to avoid fines for noncompliance, the county commissioners had to act, regardless of the funding dilemma. With the success of the 1924 bond election and the reorganization of the Department of Public Works under the dynamic Brown, work at last began on the third plan. The county began preparing plans in 1923 and by the next year began razing the Seventh Street Bridge. The War Department forced the county to begin work on the Ninth Street Bridge while the first was torn down, despite local opposition to the inconvenience and pleas for time extensions by the county. [94]

Engineers prepared several options using steel trusses to meet the military's clearance requirement. In 1923, engineers recommended a continuous-traffic lift design with a variable top chord. The main span of 400'-0" had a 33'-0" clearance, to be raised by action at two trussed towers on piers two and three. A hydraulic lift or similar equipment would have been required at each tower to change the main span's elevation for river traffic below. A platform nestled under

----

[91] For a breakdown of plan sets that groups proposals and final drawings, see "List of Available Drawings," in Appendix A of Allegheny County Department of Engineering and Construction, "Report on In-Depth Structural Inspection and Analysis of the Sixth Street Bridge," vol. 1, Aug. 1985, in File AL 02-1307.

[92] "Do Not Be Deceived by the Anti Bridge Organization So Called 'Hump,' " flyer (26 Jan. 1917), in File AL 02, ACDPW.

[93] Farrington, Highway and Bridge Program, 84-84; and "Alternate Plan & Elevation, Continuous-Traffic Lift Bridge," Drawing No. 5867 (12 Apr. 1923), ACDPW.

[94] "Action Follows County Rule That Bridge Must Go," 21 Nov. 1924, Pittsburgh Post, in Pittsburgh Bridges -- Ninth Street file, Pennsylvania Room, Carnegie Library, Pittsburgh, Pa.




THREE SISTERS BRIDGES
HAER No. PA-490
(Page 23)

the northern span provided the railroad right-of-way for the Baltimore & Ohio Railroad below street traffic at the River Avenue and Federal Street intersection. [95]

A second option, for a fixed bridge, received War Department approval. In 1924 engineers designed a structure with a parabolic top chord, its 410'-0" main span meeting the 47'-0" clearance for the required 180'-0". In addition to the three main spans, two side spans without trussing extended to the approaches, with the B&O access under the pier and embankment anchoring the northern side span. The bridge's grade of 4.175 percent exceeded the 3 percent desired, but would have meant less entanglement in procuring property or altering streets on either side of the structure. [96]

The third proposal included continuous truss bridges at Sixth and Ninth streets, designed by the city Bureau of Architecture, and a cantilever bridge at Seventh Street, designed by local architects Rutan, Russel & Wood. [97] The plans were the culmination of a long process of compromise between a dozen organizations involved in the approval process. The grades did not exceed 4 percent, but the approaches were narrower than the roadways. After clearing the fixed bridge proposal with the War Department, city and county planning departments, the state's Public Service Commission, the Citizens committee on City Plan, as well as securing support from powerful local organizations such as the Chamber of Commerce, the county submitted the drawings to the little-known Art Commission "for suggestion and approval." The commission, an advisory body created by the state in 1911 to approve Pittsburgh bridges costing more than $25,000, was expected to rubber-stamp the project. [98] While waiting for approval, the county printed specifications and opened the bidding process. The commission faced pressure for quick approval as demolition of the Seventh Street Bridge proceeded and the Ninth Street's imminent razing loomed. [99]

The commission's veto of the final plans shocked engineers and city leaders. The commission sent engineers back to the drawing board with instructions for a more attractive bridge that would not mar the downtown skyline with metal structures above the deck.

----

[95] "Alternate Plan and Elevation, Continuous Traffic Lift," Drawing No. 5866 (12 Apr. 1923), ACDPW.

[96] "Bridge No. 2 Allegheny River, Plan & Elevation," Drawing No. 6106 (15 May 1924), ACDPW.

[97] "Pushing Plans for New Bridges," Pittsburgh Telegraph, 6 June 1929, in File AL 03, ACDPW.

[98] Stanley L Roush, "The Sixth, Seventh and Ninth Street Bridges' Pittsburgh, Pa.," American Architect (5 Feb. 1928): 194.

[99] Allegheny County Department of Public Works, "Specifications for the Construction of the New Sixth Street Bridge, Pittsburgh, Pa." (New York: Evening Post Job Printing House, n.d.), in File AL 02, ACDPW; Brown, "AIIegheny County Improvements," 20; "Bridge Plans Approved by Planning Body," Pittsburgh Gazette, 17 May 1924, in File AL 03, ACDPW; Allegheny County Department of Public Works, "Application Docket No. I l, 747-24," to Public Service Commission regarding authority to reconstruct and operate a structure crossing the Baltimore & Ohio Railroad Company's right-of-way, n.d., in File AL 02, ACDPW; and "Report of the Grand Jury," 19 June 1924, regarding authority to take down existing Sixth Street Bridge, in File AL 02, ACDPW.




THREE SISTERS BRIDGES
HAER No. PA-490
(Page 24)

The requirement forced the department to reevaluate unusual ways of meeting the aesthetic mandate. Architects supplied a variety of sketches, including simple trusses, tied arches, cantilevers, and ordinary suspension bridges to the Art Commission; members had favored the last, despite known difficulties in using suspension forms at the downtown locations. After the truss design's rejection, architects again prepared a view of existing and proposed suspension bridges to help engineers visualize their task.

The architectural renderings depicted a bridge type that "would have fallen down had it been built as that particular drawing showed," noted John Lyle Harrington, a Kansas City engineer who had seen the proposals. [100] Architects played little role in the decision-making processes of the newly-organized department when their advice differed with that of the design engineers, according to Richardson. The new hierarchy within the Department of Public Works integrated architects into engineering projects, but all conflicting advice was resolved by the director, who was an engineer. Thus, while architects and engineers both presented designs, final internal department decisions favored engineering concerns. [101]

With the B&O right-of-way on the northern shore and a boulevard development anticipated by the Pittsburgh Planning Commission on the southern wharf, engineers lacked adequate anchorages. The two existing suspension bridges had suffered from anchorage movements. The county declined to take the controversial step of asking Pittsburgh to condemn businesses adjacent to the approaches. With only adumbrated approaches thus available, engineers considered more unusual anchorages and suspension systems. By thinking of the bridge as a unit, engineers deliberated whether the bridge's own forces could provide a system of support, with the piers bearing all vertical forces. [102]


Self-Anchored Suspension: Technological Diffusion

The only precedent that matched the specifications thrown back at the county's engineers was a single bridge constructed over the Rhine at Cologne, Germany, in 1915. Although the entire Department of Public Works has been credited with the design that finally succeeded in pacifying all organizations involved in the decision, and Covell has generally received main credit for his leadership, exactly who suggested the design presents a puzzling aspect of the Sixth Street Bridge's history.

City planners must have been aware of European engineering and architecture because prominent municipal reports during the first decades of the twentieth century featured examples from around the world. Frederick Law Olmsted's 1910 report about improvements necessary to

----

[100] John Lyle Harrington, "Recent Developments in Bridge Superstructures," Proceedings of the Engineers' Society of Western Pennsylvania 46, No. 3 ( 1930): 68.

[101] Wilbur J. Watson, "Bridge Architecture," Proceedings of the Engineers' Society of Western Pennsylvania 46, No. 3 (1930): 84, 87.

[102] Harrington, "Recent Developments," 68.




THREE SISTERS BRIDGES
HAER No. PA-490
(Page 25)

keep Pittsburgh's downtown transportation systems efficient and attractive included numerous examples of European structures, from municipal buildings to various bridge types. [103]

News of the self-anchored structure successfully built in Germany became available in English-language engineering literature just as the county's first truss drawings were rejected as unsuitable. George A. Hool and W. S. Kinne made an oblique reference in their book, Movable and Long-Span Steel Bridges. The authors noted that "modern suspension bridge construction is principally confined to the suspended stiffening truss type," but their broad secondary category of "suspension trusses, or braced chain bridges" included exceptions -- one of which was the 1915 Cologne bridge. Hool and Kinne included a photo of the structure that clearly showed the eye-bar chains attached to the bridge deck. Whether their picture might have conveyed the possibilities of self-anchored design is debatable. The text accompanying their description of this second category of bridges never referred to the structure as self-anchoring. [104]

By 1922 one of the better known advisors on cantilever and suspension bridge structures noted the peculiar strengths represented in the Cologne bridge's design. [105] David B. Steinman's running dispute with J. A. L. Waddell about the relative costs of suspension and cantilever forms continued a debate with roots in the Quebec Bridge collapse. The 1907 construction disaster, accompanied by the 1916 accident during a second attempt, heightened a growing preference for suspension bridges. [106] In light of the popular and engineering support for suspension structures, Steinman's first edition of A Practical Treatise on Suspension Bridges fed a growing demand for technical information about components such as eye-bars and stiffening systems. Steinman's notoriety and the fact that his book was reviewed in the engineering press make it likely that Allegheny County's engineers could have examined the first edition of his book. [107]

----

[103] Frederick Law Olmsted, Pittsburgh: Main Thoroughfares and the Down Town District (Pittsburgh: Committee on City Planning, 1910).

[104] George A. Hool and W. S. Kinne, Movable and Long-Span Steel Bridges (New York: McGraw-Hill, 1923), 324-33.

[105] D. B. Steinman, A Practical Treatise on Suspension Bridges: Their Design, Construction and Erection, 1st ed. (New York: John Wiley & Sons, 1922), 53 et passim.

[106] Petroski, Engineers of Dreams, 101-18. For Petroski's analysis of the cantilever-suspension bridge debate, see ibid., 111.

[107] Waddell and Steinman waged a turf war in professional literature during the 1910s, arguing that comparative cost of the two bridge types indicated different uses. Waddell complimented the less established Steinman on attempting to calculate costs -- primarily as a way of setting his opponent up for criticism in using approximations of weights when calculating the span lengths at which both types proved equally economical. J. A. L. Waddell, Economics of Bridgework: A Sequel to Bridge Engineering (New York: John Wiley & Sons, 1921), see especially 8-9, 104-106, 268; D. B. Steinman, Suspension Bridges and Cantilevers: Their Economic Proportions and Limiting Spans, 2nd ed. (New York: D. Van Nostrand Co., 1913); see also C. B. McCullough, Economics of Highway Bridge Types (Chicago: Gillette Publishing Co., 1929).

    Despite Waddell's attack, Steinman may have had the last laugh. He proved more open than Waddell to new ways of categorizing bridge structures, noting in 1922 the existence of new technologies, such as eye-bars and self-anchored suspension spans, which eventually blurred the boundaries of the debate. (Steven J. Fenves of Carnegie-Mellon University's Department of Civil Engineering kindly noted Steinman's contributions to the technological diffusion discussed above.)




Next Page

Page created:
Last modified: 05-May-2003

HAER Text: Haven Hawley, August 1998; Pennsylvania Historic Bridges Recording Project - II
visit site - "American Memory" at Library of Congress
visit site - National Park Service -- Historic American Engineering Record