IS42.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



.335 



Fie. 2. 



Q i O 



Fig. 1. 



m 



X. o 



three arms, and forms part of a circle, the middle arm is 2 ft. in length, 

 the other two in proportion; on each side of the arms are flat grooves 4| 

 of an inch deep and 3 in. broad, into which are inserted bars of wrought 

 iron, which connect the blocks with each other ; they are secured 

 thereto with square bolts driven through the shoulders and arms of 

 the blocks and the bar iron, and are fastened by coterels or forelocks. 

 Fig. 3. Section of Roadway and Ribs. 



Th« blocks are cast in one piece, but their construction is more easily 

 explained by supposing them to be formed of bars, each block will 

 then appear to consist of three horizontal and two vertical bars ; the 

 former cross the latter at the extremities and in the centre; there is a 

 perforation left both above and below the centre crossing, and the 

 vertical pieces cross the horizontal ones at a distance of 5 inches 

 inwards from their extremities; another perforation occurs when two 

 blocks are banded together; these perforations diminish the weight 

 of the fabric very much, when compared with a solid arch. Fig. 4, 

 is a perspective view showing two of these blocks united, and also a 

 portion of two of the ribs bolted together with horizontal bolls which 

 also form stays. 



FiR. 5. 



The whole structure consists of 6 ribs placed 6 feet apart, each 

 containing 105 of tliese blocks, built on each other, like the voussoir 

 of a stone arch. The abutments are of stone 24 feet thick, 42 feet in 

 breadth at bottom, and 37 feet at top. The span of the arch is 



23G feet, with a versed sine or rise of 34 feet. The height to the 

 soffit from low water mark is 100 feet. The spandrils of the arch 

 are filled in with iron circles, diminishing from the abutment to the 

 centre; the superstructure is of timber, planked over, supporting the 

 carriage road, formed of marl, gravel and limestone. The total 

 breadth is 32 feet, with footpaths of flogs, and enclosed by an iron 

 pallisade. The whole structure was put together and thrown over 

 the river in the short period of 10 days, without interrupting the 

 navigation, the centre being supported in two places by gearing or 

 frames of woodwork resting upon piles driven into the bed of the 

 river. The whole expense was £26,U00, of which £22,000 was sub- 

 scribed by R. Burdon, Esq., and secured at 5 per cent on the tolls. 

 In the centre of the pallisade on each side is a cast iron panel, with 

 the inscription "jV;7 desperandnm, auspice dto." The bridge is free 

 on entering the town, and id. toll is paid in recrossing or leaving the 

 town. 



Mr. Thomas Wilson, of Bishopwearmouth, was the engineer, who 

 was also engineer for a bridge at Staines, on the Thames. Mr. 

 Wilson, in conjunction with Mr. Burdon and Mr. Scarth, took out 

 a patent for this mode of construction, and erected a bridge at 

 Yarm, with less success, as the following account will show. The 

 foundation stone was laid September 3, 1803. The iron was com- 

 menced to be laid across September 3, 1804, and the arch completed 

 in 8 days. The arch was cast at the foundry of Messrs. Walker of 

 Rotherham. The form was a circular segment, 180 feet span, 27 feet 

 broad between the pallisades, with a 21 feet carriage road ; it was 

 composed of G ribs, each containing 39 perforated blocks of cast iron 

 4 feet deep and 4 inches thick. The whole weight, including pallisades» 

 was 250 tons. The abutments were of stone 30 feet thick, and the 

 flank walls 50 feet long from back of abutments, 7 feet in thickness at 

 base, and diminishing by G-inch offsets to 4 feet. The height of 

 parapet walls including fascia 4if eet. The contractors were, Mr. 

 Wheldon for the stonework, amount £2440, and Mr. Wilson, the en- 

 gineer, for the ironwork, amount £J60O. The bridge fell at midnight, 

 January 12, 180G. It had been open for foot passengers some time 

 previous to the failing. 



Architects were called in by the magistrates of Yorkshire and 

 Durham to ascertain the cause of the falling, who reported that the 

 internal masonry of the abutment was insufficient to resist the lateral 

 pressure of the arch ; they were clearly of opinion that this was the 

 occasion of its fall; a complaint was made to the same effect by the 

 surveyor during the progress of the work. The manner of placing 

 the ribs was not generally approved of, as not being calculated to 

 take an equal bearing or pressure. The old bridge, which had not 

 been pulled down, was then repaired, widened, and substituted for 

 the iron one. These particulars of the Yarm bridge are taken from 

 Grave's History of Cleveland, pub. 1808, page 68, appendix No. 1^ 

 and of the Sunderland Bridge, Surtees' History of Durham, vol. 1, 

 page 227, and three plates now very scarce, published at the time 

 of the erection, but I am sorry to say that no letter-press accompa- 

 nied them. They were engraved by R. Clarke, drawn by J. Raffield 

 and designed by G. T. Wilson. The above untoward event of the 

 falling in of the bridge at Yarm, in ray mind, is the reason why this 

 mode of construction has not been more frequently employed, and the 

 distrust of iron as a material for bridge building, as it will be seen 

 that this bridge was built only 21 years after the introduction of iron 

 for bridges. In conclusion, I beg to offer to you, at least, the novel 

 idea of rendering cast iron bridges less brittle by submitting the iron 

 to the process of annealing or to assimilate it by a gradual reduction 

 of its temperature, more to the nature of wrought iron, which ap- 

 pears to me would also increase its capability of resistance to com- 

 pression. The division of the portions of the arc into short lengths, 

 as the blocks in Sunderland Bridge, has great advantages in providing 

 for the expansion, as when so subdivided it is not so much felt, being 

 divided insensibly among the different joints. 



