HISTORY OF ENGINEERING.
Book I.
514
Fig. 521.
Fig. 522.
verse section through the main chains, exhibiting a little more than one half of the entirewidth ; the middle footway and one passage for carriages, also represents the position ofthe several lines of chains where they cross or pass over the saddles; the sections andelevation of the main pier show the position of the main chains in the other direction,or in a line at right angles with the passage across the stream.
The suspejision chains were first firmly secured to the flat cast-iron plates; the chain bars,each 10 feet in length, were then laid down by placing the five together, which constitutedone breadth ; and the consecutive lengths were thus carried on, united by flat iron platesand bolts, until the apex of the suspension piers was arrived at, the whole chain beingsupported by a timber framework placed underneath.
On the apex of each of the suspension piers was a cast-iron saddle, in which werewrought-iron rollers and brass bushes, which as the temperature varied allowed some playto the chains, and regulated any contraction or expansion of the iron; as the rollers wereself-acting, no derangement could very well take place from this cause.
Mr. Davies Gilbert furnished Mr. Telford at various times with information highlyuseful for the completion of this bridge; that gentleman calculated the dimensions to begiven to the several bars of a catenary arch formed in iron or steel upon the suspensionprinciple. He assumed the tenacity of iron to be 50,OCX) for a square inch, and its specificgravity 7-8, and Mr. James Jardine formed the following table for the construction of thechains. The first column shows the distance between the points of support; the second,the length of curve, or chain, between the points of support; the third, the axis of curve,or versed sine, of the chain; the fourth, the angle, nearly, between horizontal line andcurve, at the point of support; the fifth, the tension, or strain, on each chain by its ownweight, at either point of support; the sixth, the tension or strain on the sixteen chains bytheir own weight, at either point of support; the seventh, the weight of one chain; andthe eighth column the weight of the sixteen chains.
Feet.
Feet.
Feet.
Angle.
Tons.
Tons.
Tons.
Tons.
500
565-6
35
14° O’
20-87
333-9
10-10
161*6
560
567*5
40
15 54
18-53
296-5
10*13
162-1
560
569-5
45
17 52
16-57
265-1
10-17
162-7
The transverse section through the main chains and roadway shows the positions of theseveral parts, and the cast-iron pipes 3 inches in diameter, strutted or braced with diagonalbars ; w’ithin the pipes is a wrought-iron bolt, 1^ inch in diameter, which connects togetherthe four lines of suspending chains. The footpath in the middle of the transverse sectionis 4 feet in width, and the two other divisions are each 12 feet: between the oak guards ofeach carriage-w'ay is .a width of 7 feet 6 inches; the iron truss-rods and king-posts intro-duced beneath the roadway bars add very considerably to the strength of the platforms.In the arrangement of the several parts of this bridge the greatest attention was paid tothe manner in which they were united together, and also to allow of any portion beingtaken out and reinstated, in case of accidental fracture or injury of any kind; in thisstupendous undertaking the constant stress upon particular parts, where destructive in itseffects, could be easily remedied without endangering the entire work.