SOUTH WALES KAILWAY. 



[1852. 



method of crossing wide spans. Tlie present -w-ork of Mr. Brunei's 

 is another mode," and shows, as might have been exjjected, his 

 peculiarly oris;inal and bold conception, accompanied by extraor- 

 dinary economy, by arranging his materials m the form of a large 

 suspended truss, and attaching the roadway to suspension chains 

 kept in a state of rigidity by vertical trusses or struts inserted 

 between the chains, and a circular wrought-iron tube, spanning 

 the river, 309 feet in length. 



The bridge is 600 feet long : there are thi-ee spans over the 

 laud of 100 feet each, which are supported upon cast-iron cyUn- 

 der-s 6 feet in diameter and Ij inch thick. These cylindere were 

 sunk to an average depth of 48 feet, through numerous beds of 

 clay, quicksand, marl, &c., to the solid limestone rock, which was 

 found to dip at an angle of 45 degrees; it had, therefore, to be 

 carefully levelled hoiizontally, and the cylindere bedded level. 

 These cylinders were sunk by excavating within them, and press- 

 ing them down by heavyweights; in doing which very great 

 difficulties were overcome— immense volumes of fresh water were 

 tapjjed, requu-ing a 30 horse engine to pump them out. The 



quantity very much increased during high water, which lises 44 

 feet, and in many of the cyhnders work had to be suspended until 

 the tide receded. Although the Wye is a tidal river, and there- 

 fore salt, no salt water was found in these sinkings. Again, 

 dangers arose from sudden and extensive irruptions of soft river 

 silt, "often bursting in with such rapidity that the men had hardly 

 time to escape. Some of the strata were found covered with 

 immense conglomerate boulders, indicating a former river bed. 

 These having been overcome, the cyhndei-s were filled with con- 

 crete, composed of Portland cement, sand and gravel, which set 

 in a few days as hard as rock. The concrete is filled up to the 

 level of the roadway, so that, shoiild a cylinder decay, it might be 

 taken out and replaced in sections in safety. 



There are sis cyhnders at the west end of the main span ; upon 

 those, a standard or tower of cast-iron plate.?, fifty feet high, is 

 erected. A similar tower of masonry is bmlt at the east end, upon 

 the edge of the rocky precipice of thy Wye. Each roadway being 

 perfectly separate, we wOl describe that which is now opened. 



Fig. 1. 



In the annexed diagram, (Fig. 2) the cyhnders are b ; the standard 

 (e e e) having openings to admit the train to pass. On the west 

 standard is a cross girder of wrought-iron (s) upon which the 

 tubes (i) re^t. The tube serves to keep apart and steady the 

 towere; and to the ends of the tube are attached the suspending 

 chains. Xow, in an ordinary suspension bridge, the chains hang 

 in a festoon, and are free to move, according to the limited 

 weights passing under them ; but this flexibiUty would be inad- 

 missible in a railway bridge, and the continuity of the rail would 

 be destroyed if a very small deflexion took place when passed 

 over by a hea\"y locomotive. With a view to give this necessaiy 

 rigidity, Mr. Brunei has introduced at every third part of the 

 tube a stiff -m-ought-kon girder, connecting firmly the tube to the 

 roadway girders ; and, with the aid of other adjusting screws, the 

 suspension chains are pulled or stretched as nearly straight as 

 desirable. Other diagonal chains connect these points, so that at 

 whatever part of the Bridge an engine may be passing its weight 

 is distributed all over the tube and chains by these arrangements. 



The tube is laid upon the iron standards, but is free to move 

 upon rollers at the top of the masonry standai'd. The expansion 

 on the hottest day yet experienced has not exceeded one inch. 



The tube is strengthened within by the inti-oduction of dia- 

 phragms or discs at every 30 feet, which render it both hght 

 and stiff. 



Tlie roadway girders (d) are fonncd of a deep thin plate of iron, 

 stiffened at inter\als. At the top it has a strong triangular cell 

 to resist compression, and at the bottom a double plate of riveted 

 iron to resist extension. 



Between these side road girders are small cross girders (k) 

 (Fig. 1) riveted to them diagonally. Ujion the cros,? girdere 4 inch 

 creosoted planks are secured in the contrary diagonal direction 

 (l), so that by crossing each other stitfhe.ss is producei.!. Eighteen 

 inches of gravel are laid over all, and then the ordinary permanent 

 way upon longitudinal sleepers. 



The land abutment (a) is built of masonrj-. In the plan the 

 letters b indicate the supporting cylinder; e e are the tubes; h h 

 the cLaias radiating from the ends of the tube, which is 9 feet in 



diameter, to the saddle links on the sides of the roadway at g, 

 where thfi width is 14 feet. 



The second tube is now com- 

 plete, and may be seen in the 

 yard near the Bridge : it is ex- 

 pected to be floated next month. 

 The pontoons for can-ring one 

 end of the second tube across the 

 river are economically fonned of 

 six ordinaiT iron canal boats, 

 three being placed bottom up- 

 wards upon the lower thi'ee. 



The other end of the tut* 

 win be conveyed upon a railway 

 formed upon piles, extending 

 from the land to the six river 

 cylindeis; so that while the 

 pontoons ai-e pulled across by 

 powerful tackle at one end, the 

 latter end wiU be on a can-iage 

 rolling upon the railway to its 

 place. Strong temporaiy erc-c- 

 tions of timber are constnicted 

 upon each side of the river to 

 lift the second tube. We must 

 not omit to mention that the 

 elaborate drawings instructions, 

 and calculations, connected -snth 

 this laborious work, were made 

 under Mi-. Brunei, by his prin- 

 cipal ai»istant in London, Mr. 

 Robert P. Brereton. The resi- 

 dent engineer of the hne of tlie 

 bridge is Mr. William George 

 Owen, assisted by Messrs. Dibbin 

 and Siiycrs. 



The contractors for the iron- 

 work are Messrs. Finch & Willey, 

 of Windsor Foundry, Liverpool ; for the masonry, Mr. Sharpo. 



