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Historic American Engineering Record
Davis Avenue Bridge
HAER No. PA-487

Pennsylvania Historic Bridges Recording Project - II

Spanning Woods Run Ave. at Davis Ave.
Allegheny County

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HAER No. PA-487
(Page 8)

as diverse as paper making and steel fabrication at the turn of the century. As a way of organizing labor for projects, jobbing (or subcontracting units of work) increasingly dropped out of favor in the late nineteenth century as the engineering profession became more distinct from construction around the mid-1880s. [28] The possibilities for individuals to coordinate bridge projects declined with the American Bridge Company's incorporation in 1900. The next year, the American Bridge Company consolidated twenty-four firms under its control, encompassing half of the national bridge fabrication output. [29] As municipal departments of public works became more established, they provided bureaucracies in which engineers solidified,the status of their profession. Kaufman's exceptional persistence with individual jobbing at the century's end shows continued possibilities for lone, entrepreneurial-minded engineers despite industrial and occupational trends toward consolidation.

Fort Pitt Bridge Works

Formed out of the merger of an iron works and an engineering-and-contracting firm in 1896, the Fort Pitt Bridge Works encompassed a body of experience predating its organization. Theodore A. Straub, a young engineer who had worked with Pittsburgh firms including the Keystone Bridge Works, Pittsburgh Bridge Company, and Shiffler Bridge Works, joined with his cousin H. R. Blickle to become bridge contractors in Texas in 1894. They opened an office the following year in Pittsburgh as Straub and Blickle, offering engineering and contracting services. When the Pittsburgh Architectural Iron Works fell in financial difficulties soon after building a plant at Canonsburg, Pennsylvania, stockholders of the iron works contacted Straub and Blickle to help them pluck the new facility from the troubled company. Fort Pitt Bridge Works was incorporated in 1896, acquiring the Pittsburgh Architectural Iron Works' Canonsburg plant at a sheriffs auction on 7 May. The Fort Pitt Bridge Works subsequently produced steel components for a number of Pittsburgh bridges, including those at McKee's Rocks, the Point, Smithfield Street, Sixteenth Street, and Thirty-first Street, not to mention numerous buildings in the vicinities of Pittsburgh and Canonsburg. [30]

Cantilever Construction

Scotland's Firth of Forth railroad bridge, completed in 1889, renewed interest in cantilever construction methods, which are well-suited m long-span work over difficult terrain. By 1930, cantilever construction was considered m save money when used on spans of more than 700'-0" unless falsework was unusually inexpensive. Engineers in the early 1900s used rules of

28] Darnell, Directory, viii.

29] Darnell, Directory, 85.

30] "History of Fort Pitt Bridge Works of Pittsburg," 'typescript ca 1946, FF 1, Box 1, Group A, Fort Pitt Bridge Works Collection, Archives of Industrial Society 63:27, Hillman Library, University of Pittsburgh, Pittsburgh, Pa; and Darnell, Directory, 65.

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thumb to decide on construction methods, weighing the difficulty of constructing falsework, the structure's length, and whether it spanned a body of water on which navigation had to be maintained. Cantilever methods make erection possible without falsework, for longer spans, and without obstructing navigation.[31]

Cantilevered structures share four general characteristics, although many variations are possible. Trusses or girders serve as the major carrying members. Cantilever arms extend inward from main piers, with anchor arms extending outward to counterbalance them. The cantilever arms either meet at mid-span or support a suspended span between them. Hinges at these connections resist shear but not bending moment. The result is that primary trusses or girders convey loads m the supports through shear, with vertical reactions dominating stresses in the structure. Trusses rely upon diagonal web members to carry shear, which chords must be able to transfer. Anchor spans exert uplift forces, requiring that the ends be fastened securely anchorages. [32] The Davis Avenue Bridge is an unusual variant that defied easy classification, although it was common enough to be pictorially represented in a 1908 textbook on trusses. [33]

While economical in many situations, the lack of graceful curves and predominant linear features of most cantilevers was considered unattractive. The support systems often produced a stark frame. [34] The Davis Avenue Bridge, a modest cantilever spanning 396'-0" across a ravine in a wooded residential setting, imposed a riveted steel structure with little embellishment on verdant Riverview Park. Its functional beauty did not impress bridge critic Henry G. Tyrrell. He made a passing mention of the Davis Avenue Bridge in his 1911 History of Bridge Engineering, grouping the Allegheny City structure with another cantilever as "two highway bridges with outlines which cannot be commended." [35] As Tyrrell described it, "The Davis Ave. Cantilever ... has two lines of trusses 22 feet apart, with 20-foot panels and a road 36 feet wide, paved with asphalt on buckle plates. It is about 400 feet long with 156-foot center span and cost $26,700." [36]

He gave no indication why he so disliked the structure, assuming that his readers shared his appreciation for elegance in both appearance and design. His diagram of the Davis Avenue Bridge clearly indicated the suspended span placed between the two cantilever arms by using dotted lines for those members superfluous to the design's structural integrity, as in Figure 1.

31] John Lyle Harrington, "Recent Developments in Bridge Superstructures," Proceedings of the Engineers' Society of Western Pennsylvania 46, No.3 (Mar. 1930): 60.

32] Wilbur J. Watson, "Bridge Architecture," Proceedings of the Engineers' Society of Western Pennsylvania 46, No. 3 (Mar. 1930): 90, 92, 94.

33] A. H. Heller, Stresses in Structures and the Accompanying Deformations (New York: John Wiley & Sons,1908), 212-13.

34] Harrington, "Recent Developments," 61.

35] Henry Grattan Tyrrell, History of Bridge Engineering (Chicago: self-published, 1911), 281.

36] Tyrrell, History, 282.

HAER No. PA-487

Figure 1 -- Elevation of Davis Avenue Bridge.
Sketch by Justin M. Spivey.

Tyrrell's harsh criticism belied a concern with form over function, and must be taken in perspective. Like a growing number of engineers active during the civic improvement movements of the late nineteenth and early twentieth centuries, Tyrrell rejected strict utilitarianism as the measure by which to judge engineering achievements. That the bridge served a transportation goal at a modest cost mattered less in his eyes, perhaps, than the imposing yet somewhat ungainly appearance of the structure.

The Davis Avenue Bridge

The Davis Avenue Bridge stretches 396'-0" across the Woods Run ravine, with the bottom chord 70'-0" above the ground at mid-span. The unevenness of the ravine bottom forced workers to grade slopes before constructing the piers. Plans called for regrading the slope near the east main pier, then sinking the piers and setting all of the truss bearing pads at nearly the same elevation. The piers had to be constructed to accommodate a 2 percent grade on the eastern side of the bridge, making the task of laying masonry more exacting. [37]

A local contractor named C. M. Driver installed masonry for the Davis Avenue Bridge. The work ranged from Rose Avenue to Riverview Park, crossing the ward boundary along with the bridge. Driver used 687 cubic yards of masonry for abutments and pier foundations at a cost of $4,985.26 to the city, and he completed his work in July 1898. [38] Unfortunately, the final cost was not broken down in separate categories to reveal why Driver's original bid of $5,630.55 to complete 760 cubic yards of masonry for $6.93 a unit and 75 cubic yards of concrete for $4.85 a unit was reduced. [39]

37] City of Allegheny, "Elevation of Bridge," Drawing No. 0-49 (Oct. 1898), DEC Vault.

38] Allegheny, Municipal Reports ... 1899, 279.

39] Allegheny, Municipal Reports ... 1898, 1185.

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Driver's work included rough coursed stone piers at elevations ranging from 170.61' to 174.63'. The two main piers each consist of four stone columns, 5'-0" wide and battered 1:12 on each side, in a 22'-0" by 25'-0" rectangle, with the longer dimension parallel to the bridge. These main piers are spaced 157'-0" apart. Rough coursed stone abutments also varied in elevation, with the west at 220.18' and east at 228.10'. A distance of 96'-0" separates the west pier from the west abutment, with 93'-10" between the east pier and the east abutment. [40] During masonry work, wing walls was added to accommodate the steep site. Workers added a nearly perpendicular and an acute wing wall at the west abutment, and parallel wing walls at the east abutment. [41]

The main piers support 25'-0"-wide truss towers at L5-L6 and L14-L15, from which cantilever and anchor arms project. The tower columns are attached by two 1-1/4" bolts or tie rods to pier shoes. [42] The cantilever and anchor arms are asymmetrical, the latter being much longer. The anchor spans are comprised of five truss panels, each 19'-0" long, while the cantilever arms have but two 19'-6" panels. The suspended span between them has four additional panels the same length. Panel points U8 through U12 describe the suspended span's upper chord, and L9 through L11 its lower chord, essentially a Pratt deck truss supported by vertical members at U8 and U12. The suspended span may have bean lifted ed in place as a unit, although no extant plans indicate the method used. Expansion dams were placed in the deck at U0, U8, and U20. The cantilever construction made members L8-L9 and L11-L12 superfluous in terms of structural support. [43] These members was added mainly to continue the arc of the lower chord, providing a consistent appearance of strength. Because of the expansion joint at U8, member U7-U8 does not carry any axial load, although it is of course necessary for continuing the roadway.

The bridge could have bean built with equal cantilever and anchor arms and no suspended span, but pinning the cantilever arms to each other at mid-span would have caused excessive uplift at the and spans. Instead, the Davis Avenue Bridge has cantilever arms truncated to include a suspended span, which allows uplift to be resisted by anchor arms attached to 3'-0" rocker posts at the abutments. [44] Pins 4-1/8" in diameter join the rocker posts to the truss and to the shoes, which are anchored by 12"-long, 3"-wide, and 3/4"-thick anchor plates embedded in

40] City of Allegheny, "Masonry Plans," Drawing No. F-1085 (26 Apr. 1898), DEC Vault; and City of Pittsburgh, "Owner and Maintenance Responsibility -- Various Bridges" Drawing No. B-061, attached to letter from Department of Law to Department of Public Works, 27 Oct. 1972, in bridge inspection files, City of Pittsburgh, Department of Engineering and Construction, Bridge Division, Pittsburgh, Pa.

41] City of Allegheny, "Alterations to Masonry Work," Plan No. E-1084 (Oct 1898), DEC Vault.

42] Allegheny, "Cross Section, etc."

43] Pittsburgh, "Owner and Maintenance"; Allegheny, "Letting Plan 377."

44] Allegheny, "Cross Section, etc."

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concrete. [45] Holes for pins were reamed to size, but sections were either pinned or riveted as indicated in plans prepared by the Fort Pitt Bridge Works, apparently as shop drawings. [46] Lateral bracing is held by gusset plates pinned at truss member connections. The braces are 7/8" square rods, except for 1-7/16" square rods at the towers. [47]

The 22'-0"-wide roadway is supported by nine lines of 15"-deep built-up stringers (18" deep in the 25'-0" tower panels), carried on 5'-0"-deep latticed deck beams. As originally built the lattice work extended under the cantilevered sidewalks. [48] The only extant picture of the Davis Avenue Bridge with the original lattice work, which was painted a lighter color than the bridge (perhaps to mimic wood lattice), appears in a Fort Pitt Bridge Works promotional brochure. [49] A plan prepared before construction showed a cross-section of two possible options for surfacing the roadway. On top of the stringers, engineers debated letting bids for a two-layer wood surface, or for buckle plates topped with concrete and 1-1/2" of asphalt. [50] For the sidewalks, each cantilevered 8'-0" with a 3'-6" railing, the options was two 4" x 16" wooden stringers supporting a single layer of timber decking or three I-beam stringers (one a roadway member) supporting a two-layer wooden wearing surface. Bids was accepted on the latter options, as indicated in a letting plan and completed drawings. The final letting plan also noted roadway and sidewalk live loads of 100 pounds per square foot on stringers and floor beams and 70 pounds per square foot on the trusses [51]

The Chester B. Albree Iron Works prepared drawings for the railings and lamp posts, which were installed in 1898. The railing design features riveted lattice in the lower two-fifths of each panel, with overlapping arcs in the upper three-fifths. Lamp posts, since removed, featured a leaf motif encircling the posts just above the railing joints. [52] Albree's firm advertised as a bridge builder in Allegheny from 1896 to 1899, but by 1901 the company specialized in railings. [53] Commemorating the bridge's completion in 1898, two name plates listed Robert McAfee, Allegheny's directory of the Department of Public Works; G. C. Langenheim,

45] City of Allegheny, "Details of Built Shoes," Drawing No. F-1112 (Oct. 1898), DEC Vault; ibid., "Masonry Plans."

46] City of Allegheny, "Details of Trusses," Drawing No. F-1090 (Oct. 1898), DEC Vault.

47] Allegheny, "Strain Sheet"

48] Allegheny, "Strain Sheet"

49] "Records (1896-1949) of Fort Pitt Bridge Works," FF 1, Box 1, Group A, Fort Pitt Bridge Works Collection, Archives of Industrial Society 63:27, Hillman Library, University of Pittsburgh, Pittsburgh, Pa

50] City of Allegheny, "Buckle Plates," Drawing No. F-1094 (Oct. 1898), DEC Vault.

51] Allegheny, "Cross Section etc."

52] City of Allegheny, "Detail of Lower Part of Lamp Posts," No. F-1086 (Oct. 1898), DEC Vault.

53] Darnell, Directory, 58

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superintendent of the Bureau of Engineering; Gustave Kaufman, engineer and contractor; and Fort Pitt Bridge Works of Pittsburgh, the builder. [54]

William E. Howley received the contract for grading Davis Avenue up to the bridge, leveling the roadway between Brighton Road and Rose Avenue in Ward Eleven, improving the street up to the abutments. He moved 24,449 cubic yards of earth for the 50-foot wide section, completing the project in February 1899 at a cost of $8031.81. [55] It is possible that Howley's services was employed earlier in grading the pier slopes. W. O. Plank, a contractor with previous experience on bridge projects in the Pittsburgh area, completed paving on the structure's roadway. [56]


The litany of small contractors who assisted Kaufman in constructing the Davis Avenue Bridge and improved the adjacent roadway in 1898-99 were soon eclipsed by the consolidation of bridge companies in a single entity that soon dominated the industry in Pittsburgh and across the country. Within two years of the Davis Avenue structure's completion, half of the country's bridge-building capacity combined in one company as part of the first great merger movement that swept America. The fabrication, financing, and technical resources available to immense engineering firms made it more difficult for independent contractors like Kaufman to compete. The bridge's construction gives evidence of Allegheny's growth and the place of public works at the end of the nineteenth century. Within a decade, Allegheny would be annexed and overshadowed by the more powerful city of Pittsburgh across the river. Corporate and municipal consolidation made projects like the Davis Avenue Bridge seem insignificant when compared to grander structures sometimes produced by large business and governmental entities.

Unlike the elaborate steel arch constructed over Panther Hollow in Pittsburgh's Schenley Park in 1895-96, the Davis Avenue Bridge was a modest structure, designed for function more than form. The latter saves as a reminder of success measured by standards of the community in which it was built, not those imposed by later generations.

54] City of Allegheny, "2-Name Plates for Davis Ave. Bridge," Drawing No. D-43 (ca 1898), DEC Vault.

55] Allegheny, Municipal Reports ... 1899, 278.

56] City of Pittsburgh, Annual Reports of the Executive Departments of the City of Pittsburgh for the Year Ending January 31, 1912, vol. 1 (Pittsburgh: Pittsburgh Publishing Co.,1912), Table 3, "Tabulated Data Relating to the Free Bridges Located Within the Corporate Limits of Greater Pittsburgh, Pennsylvania." Table 3 is an invaluable reference that lists all city-owned bridges as of 1912, with dimensions, contractors, contract prices, dates of construction, and limited data about previous bridges at certain sites.

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Allegheny, city of. Municipal Reports for the Fiscal Year Ending February 28th, 1897. Oil City, Pa.: Derrick Publishing Company, 1897.

_____. Municipal Reports for the Fiscal Year Ending February 28th, 1898. Allegheny, Pa.: T. A. McNary, 1898.

_____. Municipal Reports for the Fiscal Year Ending February 28th, 1899. Oil City, Pa.: Derrick Publishing Company, 1899.

_____. Park Commission. Second Annual Report of the Park Commission of the City of Allegheny, January 1st, 1870. Pittsburgh: W. G. Johnston & Co., 1870.

Baldwin, Leland D. Pittsburgh: The Story of a City. Pittsburgh: Univ. of Pittsburgh Press, 1937.

Church, Samuel Harden. Short History of Pittsburgh, 1758-1908. New York: DeVinne Press, 1908.

Darnell, Victor C. Directory of American Bridge-Building Companies 1840-1900. Occasional Publication No. 4. Washington, D.C.: Society for Industrial Archeology, 1984.

Everts, L. H. History of Allegheny Co., Pennsylvania. Philadelphia: L.H.Everts & Co., 1876.

Harrington, John Lyle. "Recent Developments in Bridge Superstructures." Proceedings of the Engineers' Society of Western Pennsylvania 46,No. 3 (Mar. 1930): 52-76.

Heller, A. H. Stresses in Structures and the Accompanying Deformations. New York: John Wiley & Sons, 1908.

History of Allegheny County, Pennsylvania. Chicago: A.Warner & Co.,1889.

Hool, George A., and W. S. Kinne. Movable and Long-Span Steel Bridges. New York: McGraw-Hill, 1923.

Hopkins, G. M. Atlas of the Cities of Pittsburgh and Allegheny, from Official Records, Private Plans and Actual Surveys. Philadelphia: G. M. Hopkins, 1882.

_____. Atlas of the County of Allegheny, Penna., from Official Records, Private Plans and Actual Surveys Philadelphia: G. M. Hopkins, 1876.

_____. Map of the Cities of Pittsburgh, and Allegheny, Showing the New Arrangement of the Wards, from Official Records and Actual Surveys. Philadelphia: G. M. Hopkins, 1876.

Kaufman, Gustave. "The Reconstruction of the Ninth Street Bridge, Pittsburg, Pa." Proceedings of Engineers' Society of Western Pennsylvania 8 (1892): 189-226.

Kelly, J. M. Handbook of Greater Pittsburgh. 1st ed. Pittsburgh:J.M.Kelly, 1895.

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Pittsburgh, city of. Annual Reports of the Executive Departments of the City of Pittsburgh for the Year Ending January 31, 1912. Vol. 1. Pittsburgh:Pittsburgh Publishing Co., 1912.

Pittsburg Post.

Tyrrell, Henry Grattan. History of Bridge Engineering. Chicago: self-published, 1911.

U.S. Works Progress Administration, comp. Story of Old Allegheny City. Pittsburgh: Allegheny Centennial Committee, 1941.

Watson, Wilbur J. "Bridge Architecture." Proceedings of the Engineers' Society of Western Pennsylvania 46, No. 3 (Mar. 1930): 77-94.

Wilkins, W. G. "The Reconstruction of the Sixth Street Bridge at Pittsburg, Pa." Proceedings of the Engineers' Society of Western Pennsylvania 9 (1895): 143-67.


Archives of Industrial Society, Hillman Library, University of Pittsburgh, Pittsburgh, Pa. City Photographer's Collection and Port Pitt Bridge Works Collection.

Carnegie Library of Pittsburgh, Pittsburgh, Pa. Allegheny Regional Branch.

_____. Pennsylvania Room.

City of Pittsburgh, Department of Engineering and Construction, Bridge Division, Pittsburgh, Pa. Bridge inspection reports and vault drawings files.

Henry Heinz Regional History Center, Pittsburgh, Pa. Archives of the Western Pennsylvania Historical Society.

Pennsylvania State Library, Harrisburg, Pa.

Pittsburgh History and Landmarks Foundation, Pittsburgh, Pa.

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HAER Text: Haven Hawley, August 1998. Revised March 2001.; Pennsylvania Historic Bridges Recording Project - II
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