BRIDGES AND
TUNNELS OF
ALLEGHENY COUNTY,
PENNSYLVANIA
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HAER
Smithfield Street Bridge, Pittsburgh, PA
01 Cover Page
02 Foreword
03 Ferries
05 Monongahela
Bridge and
Fire
12 Masonry
17 Removal
of Old and
Erection of
New Bridge
18 Flooring
19 Ornamental
Towers and
Painting
22 Alterations
23 Footnotes
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Smithfield Street Bridge, Pittsburgh, PA Historic American Engineering Record PA-2 page 5
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Monongahela Bridge Description and Fire Llewellyn Edwards describes the Monongahela Bridge as follows: "The substructure consisted of two abutments and seven piers of stone masonry. The superstructure had eight covered wood truss spans and an overall length of 1500 feet." (10) Richard Allen also comments on both the Monongahela and Allegheny Bridges (the latter not finished until 1819). The Monongahela was a Burr truss structures and Allen states that -- "Its outstanding feature was the toll collector's living quarters. He was housed in a small apartment built above the barn-like portal of the Pittsburgh side." (11) The Burr truss which appears so frequently in the chronicles of early American bridge construction, was named for Theodore Burr (1771-1822), a well known bridge designer of his day. Like all his contemporaries, he, for all but very short spans, combined the arch and truss (witness the "catenarian arches" of the Gazette account quoted earlier), but instead of combining them by strengthening the arch by the truss, as did the rest, he strengthened the truss by the arch. His design was in reality merely a series of king posts and it is safe to say that the majority of wooden covered bridges built in the United States were of the Burr truss design. (12) The designer of both the Monongahela and the Allegheny Bridges was Lewis Wernwag (1769-1843) who was perhaps the most famous of all early American bridge engineers. Born in Germany he came to the United States at the age of seventeen, settling in Philadelphia. He specialized in wooden truss spans, his first famous work being a bridge of a single span constructed in 1812 over the Schuylkill River at Philadelphia. He later constructed many highway and railroad bridges. A letter from his son John to Samuel Smedley published in Engineering News, August 13, 1885, includes a list of twenty-nine bridges built by his father during his active career of twenty-seven years. (13) Of all these bridges the Monongahela was not the least famous. Joseph H. Thompson was the builder of the Monongahela Bridge and a contract was made with him on July 9, 1816 to construct Wernwag's "double-passage bridge covered from end to end." The contract price was $110,000. (14) The Monongahela span gave many years of good service to the developing Pittsburgh region but it disappeared in ten minutes in a long trailing line of smoke and flame at two o'clock in the afternoon during the Great Fire of April 10, 1845, (15) one of those huge conflagrations that devastated American cities in the nineteenth century. (16) At the time of its destruction it was still the only bridge over the Monongahela at Pittsburgh.
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Introduction Last modified on
30-Sep-99
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