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Dunlap's Creek Bridge
was the first cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...
, metal arch bridge
An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side...
in the United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. It was designed by Richard Delafield
Richard Delafield served as superintendent of the United States Military Academy, was Chief of Engineers, and was a major general in the Union Army during the American Civil War.-Biography:...
and built by the United States Army Corps of Engineers
The United States Army Corps of Engineers is a federal agency and a major Army command made up of some 38,000 civilian and military personnel, making it the world's largest public engineering, design and construction management agency...
. Constructed from 1836 to 1839 on the National Road
The National Road or Cumberland Road was the first major improved highway in the United States to be built by the federal government. Construction began heading west in 1811 at Cumberland, Maryland, on the Potomac River. It crossed the Allegheny Mountains and southwestern Pennsylvania, reaching...
in Brownsville, Pennsylvania
Brownsville is a borough in Fayette County, Pennsylvania, United States, officially founded in 1785 located 35 miles south of Pittsburgh along the Monongahela River...
, it remains in use today. It is listed on the National Register of Historic Places
The National Register of Historic Places is the United States government's official list of districts, sites, buildings, structures, and objects deemed worthy of preservation...
and is a National Historic Civil Engineering Landmark (1978).
There have been four structures on this site. The first two collapsed in 1808 and 1820. The third, a wood frame structure, needed replacement by 1832.
This bridge is constructed using five parallel tubular ribs, each made of 9 elliptical segments to form the 80 feet (24.4 m) arch.