crushed timbering

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- arch timbering

SUBJECT AREA: Civil engineering

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The son of Polycarp Roebling, a tobacconist, he studied mathematics at Dr Unger's Pedagogium in Erfurt and went on to the Royal Polytechnic Institute in Berlin, from which he graduated in 1826 with honours in civil engineering. He spent the next three years working for the Prussian government on the construction of roads and bridges. With his brother and a group of friends, he emigrated to the United States, sailing from Bremen on 23 May 1831 and docking in Philadelphia eleven weeks later. They bought 7,000 acres (2,800 hectares) in Butler County, western Pennsylvania, and established a village, at first called Germania but later known as Saxonburg. Roebling gave up trying to establish himself as a farmer and found work for the state of Pennsylvania as Assistant Engineer on the Beaver River canal and others, then surveying a railroad route across the Allegheny Mountains. During his canal work, he noted the failings of the hemp ropes that were in use at that time, and recalled having read of wire ropes in a German journal; he built a rope-walk at his Saxonburg farm, bought a supply of iron wire and trained local labour in the method of wire twisting.

At this time, many canals crossed rivers by means of aqueducts. In 1844, the Pennsylvania Canal aqueduct across the Allegheny River was due to be renewed, having become unsafe. Roebling made proposals which were accepted by the canal company: seven wooden spans of 162 ft (49 m) each were supported on either side by a 7 in. (18 cm) diameter cable, Roebling himself having to devise all the machinery required for the erection. He subsequently built four more suspension aqueducts, one of which was converted to a toll bridge and was still in use a century later.

In 1849 he moved to Trenton, New Jersey, where he set up a new wire rope plant. In 1851 he started the construction (completed in 1855) of an 821 ft (250 m) long suspension railroad bridge across the Niagara River, 245 ft (75 m) above the rapids; each cable consisted of 3,640 wrought iron wires. A lower deck carried road traffic. He also constructed a bridge across the Ohio River between Cincinnati and Covington, a task which was much protracted due to the Civil War; this bridge was finally completed in 1866.

Roebling's crowning achievement was to have been the design and construction of the bridge over the Hudson River between Brooklyn and Staten Island, New York, but he did not live to see its completion. It had a span of 1,595 ft (486 m), designed to bear a load of 18,700 tons (19,000 tonnes) with a headroom of 135 ft (41 m). The work of building had barely started when, at the Brooklyn wharf, a boat crushed Roebling's foot against the timbering and he died of tetanus three weeks later. His son, Washington Augustus Roebling, then took charge of this great work.

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