1865.] in the Chains of Suspension Bridges. 141 



has been thrown away upon what is worse than wasted material, inasmuch 

 as that material,. remaining as load only, has to be carried by the chains, 

 and correspondingly weakens the structure. 



I am also acquainted with a very recently constructed suspension bridge 

 in which some of the links, which are 10 inches wide, have the holes in 

 their heads but 2 inches, instead of 6| inches, in which case more than two- 

 thirds of the iron in the links is useless. 



The first time my attention was seriously called to this important sub- 

 ject was when Mr. Vignoles entrusted my late firm of Fox, Henderson, 

 and Co., with the manufacture of the chains of the great suspension bridge 

 for carrying a military road over the Dnieper, at KiefF, which was con- 

 structed by him for the Russian Government. 



As the chains for this bridge weighed upwards of 1600 tons, upon 

 which the expense of transport was very heavy, they having to be shipped 

 to Odessa, and thence carted over very bad roads for upwards of 300 

 miles to KiefF, it was considered of the first importance to ascertain 

 whether or not they were well proportioned ; and accordingly a proving- 

 machine was specially prepared, of power sufficient to pull into two any 

 link intended to be used on this bridge. 



These links, as shown in the drawing attached to the contract (see 

 fig. ]), were, for convenience of transit, but 12 feet long from centre to 

 centre of pin-holes, 10|" wide by 1" thick in their body or smallest part, 

 with a head at each end also 1" thick, swelled out to 16" in width, so 

 as to allow of holes for receiving pins 4|" in diameter. The cross-sectional 

 area of these pins was 15'9 inches, or rather more than 50 per cent, in 

 excess of the cross-sectional area of the link at its smallest part. 



According to the usual mode of ascertaining the size of these pins, by 

 making them of such dimensions as to resist the force required to shear 

 them, they possessed upwards of a third more section than was thus 

 shown to be necessary. Still, in practice, a pin of this size proved alto- 

 gether disproportionate to the size of the links, and required to be increased 

 from 4^" to 6^" diameter before it was possible to break a link in its body 

 or narrowest part fracture in every previous case taking place at the hole, 

 and through the widest part of the head, as shown in fig. 2. 



The iron in the links for this bridge was of a very high quality, and was 

 manufactured by Messrs. Thorneycroft and Co., from a mixture of Indian 

 and other approved pig-iron, and required a tensile strain of about 27 tons 

 per sectional inch to break it ; so that taking the narrowest part at, say 

 10 inches, a strain of 270 tons ought (had the size of the pin been in 

 proper proportion) to have been required to pull it into two ; instead of 

 which, so long as the pins were but 4| inches in diameter, the head tore 

 across (as shown at fig. 2) at its widest part with about 180 tons, or two- 

 thirds only of the strain desired and provided for as far as the size of the 

 body of the links was concerned. 



This unexpected result led to the belief that the size of the heads was 



M 2 



