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HISTORY OF ENGINEERING.
Rook I.
The main chains were hoisted in the following manner ; six strong rope cables werestretched across the tops of the supporting pyramids, which were made to carry a temporaryplatform; on this was laid the chain which was to be united with that portion to bebrought up from the fixed points in the rock galleries to the top of the pyramidal towers.When this junction was made, the platforms of wood were removed, the rope cables wereslackened, and the chain lowered to its proper curvature. The side railing was then fixed,and the road platform constructed in a similar way to that over the IMenai, the severalparts of the chains, and method of fixing them, being alike.
The Union Suspension Bridge., over the Tweed, five miles from Berwick, constructed byCapt. S. Brown, R. N., was the first large bar chain bridge executed in Great Britain ; itwas finished about 1820.
Tim chord line, or distance between the points of suspension, is 449 feet, and the de-flection 80 feet. There are twelve main chains placed in pairs, and forming three ranges,one under the other, on each side of the bridge, and about 19 inches apart. Each link isformed of a rod 2 inches in diameter, and 15 feet in length, with an eye at each end forwelding. On the Scotch side of the Tweed the suspension pier is of ashlar stone, formedlike a pyramid, 60 feet in height, 36 feet in breadth, and 17 feet 6 inches thick at bottom.The arched opening is 12 feet wide and 17 feet high. On the other side of the river thepier is built on the rock, which is precipitous. 'Hie roadway is 387 feet in length, and18 feet wide between the parapets, and is supported by vertical rods, 1 inch in diameter,and placed 5 feet apart. The chains contain 38 square inches of iron, and its strength hasbeen computed equal to bear 1101 tons.
The Sewhaven Suspension Pier was also erected by Capt. S. Brown, R.N., in 1821, byorder of the Trinity Pier Company; its extreme length is 700 feet, and its width 4 feet.It has three divisions, each 209 feet span, with 14 feet deflection. The pier-head is 60 feetwide, and 50 feet long, supported upon 46 piles driven about 8 feet into the clay. Theland pier is of solid masonry, 6 feet square, and 20 feet high ; the main bars pass over thetop, and the hack-stays form an angle of 45 degrees to the chord line. There are two mainchains formed of rods 1 inch and 1£ inch in diameter, and 10 feet in length. The road-way is supported by two longitudinal iron side bars, which are held up by the verticalrods. The cast-iron standards that support the main chains are triangular frames cast inone piece, and the main chains lie on cast-iron saddles.
Brighton Chain Pier , opened in November, 1823, was designed by Capt. S. Brown, R.N.,who first suggested that the chains should be made of straight wrought-iron rods or bars,from 5 to 15 feet in length, with either welded eyes, or holes drilled at their ends, by whichthey might be connected either by short links or pins ; this invention he patented in 1817.
The Brighton pier extends into the sea 1014 feet from the face of the esplanade wall,and its entire length is 1136 feet, formed with four openings, each spanning 255 feet, witha deflection of 18 feet. The extreme breadth of the platform is 13 feet, and in the clearwidth 12 feet 8 inches.
The pyramidal suspension towers are made of cast-iron, united by an arch at the top ;they are 10 feet apart and 25 feet high, and each weighs about 15 tons: they are placed onpiles driven firmly into the chalk, which stand out about 13 feet above high water ; thesegroups of piles are 256 feet distant from each other, and leave a clear opening of 227 feetThe pier-head has the form of a T, and 150 piles were used, besides braces and diagonals ;over them the platform is 80 feet by 40 feet, which is paved with granite 12 inches thick,the weight of which is upwards of 200 tons.
Each of the ordinary groups of piles consists of twenty. The four main chains on eachside, which carry the platform, are formed of wrought-iron, round eye-bolts, about 2 inchesin diameter, 10 feet long, and weighing 112 lbs. each ; they are united by open couplinglinks I,* inches deep, and 1 inch thick, with bolt pins 2 inches in diameter. The totalarea of the section of the iron in the chains is 25 square inches. The platform is suspendedby vertical rods 1 inch in diameter and 5 feet apart.
Montrose Suspension Bridge , over the River Esk, was completed in the year 1829. Theiron work was provided by Captain Samuel Brown for the sum of 9430/., and the masonryof the towers cost 90S0/. ; this was exclusive of the land arches, which were a part of theold bridge.
From the centre of one tower to that of the other was 432 feet; the deflection of thechain, or versed sine of the catenary, 42 feet; the length of the suspended roadway 412 feet,and the width 12 feet; height of the roadway above the low water line 21 feet, and thatof the towers 68 feet. The dimensions of the base of the tower at the level of the roadwayare 40 feet by 20 feet: the archways through them 16 feet in width, and 24 feet in height;they are built of red sandstone ashlar, and are carried on piles. On each side were twomain chains 12 inches apart, each composed of four bars of iron 5 inches in width, 1 inchin thickness and 10 feet in length, united by plates and wrought-iron pins. The roadwaywas suspended by 1 •J-iuch perpendicular rods, placed 5 feet apart ; these had at their lowerends stirrup irons, which carried cast-iron bearers, over which the road was formed. A