Pratt, Thomas Willis

SUBJECT AREA: Civil engineering

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b. 4 July 1812 Boston, Massachusetts, USA

d. 10 July 1875 Boston, Massachusetts, USA.

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American civil engineer, inventor of the Pratt truss.

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The son of Caleb and Sally Pratt, Thomas Pratt attended public school in Boston before going on to the Rensselaer School (now the Rensselaer Polytechnic Institute) in Troy, New York. While at school, his spare time was spent assisting his father, a well-known architect, in his practice. He is said to have drawn a complete set of plans for a substantial house when only 12 years old. At the conclusion of his studies, he was offered a teaching position at Rensselaer but turned it down as he was planning an engineering career; he became a government assistant on the construction of dry docks at Charleston, South Carolina, and Norfolk, Virginia.

After this experience of government work, he turned to railroad construction, first with the Boston and Lowell and Boston and Maine railroads, followed by many others. In this work, he became involved in bridge construction, mostly as consulting engineer. His best-known bridge was that over the Merrimack River at Newburyport, Massachusetts, which he built with six long timber spans and a metal drawspan. He also invented a new method of ship propulsion, a form of steam boiler, an equalizer for drawbridge supports and an improved form of combined timber and steel truss; he is best known, however, for the Pratt truss. This did not truly come into its own until the inception of all-metal construction for bridges, by which time it was too late for Pratt to gain much financial reward from it.

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Further Reading

D.B.Steinman and S.R.Watson, 1941, Bridges and their Builders, New York: Dover Books.

D.Malone (ed.), Dictionary of American Biography, New York: Charles Scribner.

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