1911 Encyclopædia Britannica/Menai Straits

MENAI STRAITS, a channel of the Irish Sea, separating Anglesea from Carnarvonshire, N. Wales, extending 14 m. from Beaumaris to Abermenai, and varying in breadth from 200 yds. to 2 m. It is famous for the suspension and tubular bridges which cross it. The suspension bridge carries the Holyhead road from Bangor. Designs were prepared by T. Telford. It was begun in 1819; the first chain carried over in April 1825; the last in July of the same year, and the bridge opened to the public the 30th of January 1826. The cost was £120,000. The length of the chains (from rock-fastenings) is 1715 ft., and between the piers 590 ft.; the length of the roadway between the piers is 550 ft. and the total roadway length 1000 ft.; the height of the roadway from the spring tide high-water level is 100 ft.; the breadth of the roadway including two carriage-ways and a footpath is 30 ft. The sixteen suspending chains are carried 60 ft. through rock. Their sustaining power has been calculated at 2016 tons, while the whole weight of the suspended part of the bridge is only 489 tons. During a gale a slight oscillation is noticeable on the bridge itself and from the shore. The tubular bridge carries the London & North Western railway. Here the channel is about 1100 ft. wide, and divided in the middle by the Britannia Rock, bare at low water. The tide generally rises 20 ft., with great velocity. The principal measurements are: each abutment 176 ft.; from abutment to side tower, 230 ft.; from side tower to central tower, 460 ft.; breadth of each side tower at road-level, 32 ft.; breadth of centre tower, 45 ft. 5 in. The total length of the roadway is 1841 ft. 5 in. The Britannia tower measures at its base 62 by 521/2 ft.; with a total height of 230 ft. There are 101 ft. between the sea at high tide and the bridge roadway bottom. The limestone used is from Penmon, 4 m. from Beaumaris. Four stone lions couchant guard the approaches to the bridge. The first tube of the tubular bridge was deposited in its place on the 9th of November 1849, the last on the 13th of September 1850. The total cost was £621,865. The engineer of the tubular bridge was Robert Stephenson, who was assisted by Sir William Fairbairn and Eaton Hodgkinson.