34 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Febuvabt, 



(luality from the Baltic, and the whole of it was subjected to the 

 process of Kyaii's patent. 



The arched ribs are shown in Plate III., figs. 1 and 2; and in 

 detail, figs. 3 to 12. The spans of 116 feet, have a versed sine of 

 33 feet, the radius being 68 feet. The ribs are constructed of 

 Dantzic deck deals, 11 inches wide by 3 inches thick, dressed and 

 cut to lengths of from 20 feet to 16 feet. The first course of the 

 rib is two deals in width, bent over the centre, and tlie next is one 

 whole and two half deals, and so on alternately until the whole rib 

 is formed ; each rib consists of fourteen deals in thickness, exclu- 

 sive of tlie weathering or capping on the top ; tlie ends of the deals 

 throughout are butted against each other, and arranged so that no 

 two of the radiating joints may come together. A layer of strong 

 brown paper dipped in boiling tar, is put between all the joints to 

 bed them and to exclude the wet. The whole of the deals are well 

 fixed together with the best U inch oak trenails placed »• feet 

 apart, and each treiuiil is of a suificient length to go through three 

 thicknesses or the deals. The ends of the deals are all inserted 

 into the cast-iron plates already described, bedded in patent felt 

 and tar, and well caulked. 



Diagonal side braces 6i inches by 6,1 inches, (shown in fig. 2, 

 Plate III.), are fixed between the ribs \vith wrought-iron bars l^ 

 inch diameter, at intervals of aliout 29 feet apart, to bind and con- 

 nect the whole together. From the ribs, a series of radiating and 

 horizontal struts, are carried up in the manner shown in the en- 

 gravings ; the ends of all the struts are doulile tenoned into proper 

 mortices cut to receive them, in the timbers and ribs. A spandril 

 beam 13,1 inches square, (figs. 3, 4, 8, and 9, Plate III.,) is placed 

 about the middle of the spandril, inclining upwards to the crown 

 of the arch, and butting against a horizontal piece of the same 

 dimensions at the top. The struts below this beam radiate to the 

 centre, and those above are perpendicular to the roadway. One of 

 the radiating struts in each spandril, called in the drawings the 

 spandril strut, (figs. 5 and 6, Plate III.,) is continued on from the 

 rib up to the longitudinal beams, and is firmly connected by iron 

 straps and bolts to them and the spandril beams, and the former 

 are then secured down to the masonry with iron bolts, which run 8 

 feet into the ashlar work. In considering this geometrical arrange- 

 ment of strutting in the spandrils, it will be evident how much 

 rigidity is produced : a weight coming upon one haunch of the arch 

 is resisted on the opposite haunch, by the spandril strutting, and 

 especially by the main strut, ccmnected as it is with the weight of 

 masonry laid hold of by the bolts, from the main longitudinal 

 beam. 



The longitudinal beams, 13^ inches square, are fixed and laid the 

 full length of the structure, to the gradient of the railway, above 

 which the joists, 13i inches by 6f inches, are laid 4. feet apart from 

 centre to centre, and spiked down upon them. The ends of all 

 the joists are rounded, and project about 2 feet 6 inches over the 

 longitudinal beams, fig. 10, and the whole are then covered with 

 planking, 11 inches by 3 inches, laid longitudinally, and properly 

 spiked down and caulked ; this platform is then covered with a 

 composition of boiling tar and lime, mixed with gravel whilst it is 

 being laid on ; thus forming a coating completely impervious to 

 the wet. At the meeting of the longitudinal beam and the crown 

 piece, an iron strap is bound over them and the longitudinal beam, 

 and it is then run through the rib, and screwed up underneath it. 

 Another strap is put round the rib and the spandril beam, about 

 12 feet further down on each side, and another at each of the 

 spandril struts. An open railing, 5 feet high, is fixed alongside 

 each side of the bridge, the upright standards are 8 feet apart, 

 fixed to every alternate joist, and five horizontal rails, halved and 

 spiked to them, run the full length. 



The total width of the Ouse Burn Viaduct, measuring within the 

 railing, is 26 feet, from which a footpath is taken, 5 feet wide, 

 separated from the railway by a line of railing on tlie south side, 

 as shown in fig. 2. 



In constructing both the masonry and timber work of this via- 

 duct, the scaffolding and the centering used were very light and 

 simple. For the former, a temporary railway, 35 feet high, raised 

 upon upright bearers, struts, &c., was laid the full length, on each 

 side of the intended structure; and was afterwards raised, as the 

 building proceeded, to within a few feet of the height of the finished 

 platform. On this railway temporary cranes were placed, spanning 

 from one rail to the other, connected at the top with beams of tim- 

 ber, and fitted up with proper winches, blocks, chains, &c. &c. ; 

 these cranes were generally worked by four men. The centering 

 for turning the ribs and building all the timber work was exceed- 

 ingly light ; it was composed merely of three ribs, weighing about 

 18 cwt. each, or 2 tons li cwt. fur each rib. A whole centre could 



be removed in a day from one arch, and fixed in its place for 

 another arch, by about twenty men, employing the travelling 

 cranes. 



The WiLLiNGTON ViAnicT is precisely the same in construction 

 and design as that at the Ouse Burn ; but diflfers in its dimensions, 

 and although it is not so high, it is longer, and has two more tim- 

 ber arches of greater span. The total length is 10 ju feet, and the 

 height is 82 feet. There are seven timber arches and six stone 

 piers, with two stone abutments; five of the arches are 120 feet 

 span each, and two 115 feet span each ; the width between the 

 railing on each side is 21 feet, being just sufficient for the double 

 line of railway, as there is no footpath upon this viaduct. Two 

 of the piers are built upon piles 36 feet long, at a depth of about 

 50 feet below the surface, as there is a great extent of alluvial de- 

 posit immediately on the site, which is frequently covered, during 

 high tides or floods, by the river Tyne flowing up at the small 

 burn. 



Both these viaducts span over numerous houses and manufac- 

 tories. 



The method of building the viaduct at Willington was somewhat 

 difl'erent from that adopted at the Ouse Burn, and perhaps not so 

 unique ; inasmuch as there were no travelling cranes or temporary 

 railway, and the removal of the centres was attended witli greater 

 labour, for while at the Ouse Burn the removal of a centre occu- 

 pied twenty men, with the cranes, only one day, the same work 

 employed twenty men for ten days at A\'illington. The masonry 

 of each pier was set with a fixed or jib crane, of a sufficient height 

 to hoist all the stones, having the usual counterbalance at the 

 opposite end of the horizontal beam. 



In this system of timber bridge building, the straight trussing in 

 the main principle of support, is «lispensed with, for the spandril 

 framing should not be looked upon as partaking of that character ; 

 it is merely a continuation of the wood-work, to convey the weight 

 coming upon the roadway, on to the simple curved rib, and all 

 timbers in a state of tension are avoided, for when a weight comes 

 upon the roadway, the whole of the structure undergoes compres- 

 sion. 



It is not meant to advocate timber bridges on this or any prin- 

 ciple in preference to stone, or other more durable material ; but 

 it will not be denied, that the great saving of capital in the first 

 instance is a very important argument in favour of their adop- 

 tion. 



The actual cost of the Ouse Burn Viaduct, including all contin- 

 gencies and extras, was: — for the masonry, 17,235/.; for the car- 

 pentry, 7,265/. ; making together, 24,500/. 



The total cost of the Willington Viaduct, was : — masonry, 13,153/. ; 

 carpentry, 10,349/. ; together, 23,502/. 



The piers, Mr. Green observes, are stronger than necessary for 

 the weight of the superstructure, for the directors of the New- 

 castle and North Shields Railway not only being sceptical as to the 

 safety of this novel mode of construction, but having a desire to 

 finish all the bridges on the line with stone arches, wished the ma- 

 sonry to be made of such solidity and bulk as to bear stone arches 

 if required, and the piers and abutments were, therefore, built 

 accordingly. The additional cost for building stone arches, how- 

 ever, <m a fair calculation, was found to amount to 9,000/. for the 

 Ouse Burn Viaduct, which would have made a total of 33,500/. 

 The centering « ould luive cost at least 3,000/. for each viaduct, so 

 that at a moderate calculation tlie actual saving of capital is up- 

 wards of 10,000/. 



Messrs. Green have just completed a large viaduct, on precisely 

 the same principle as those of the Ouse Burn and Willington Dean, 

 for his grace the Duke of Buccleuch, across the South Esk at Dal- 

 keith, in connexion with the Edinburgh and Dalkeith Railway, and 

 for the transit of coal from the collieries of his grace in that neigh- 

 bourhood ; it has only a single line of railway and a footpath. The 

 total length of this work is 830 feet, the height is 87 feet to the 

 platform, and the width across between the railing is 14 feet. It 

 has seven arches, five of 120 feet, and two of 110 feet spiin each, 

 with a versed sine of 30 feet. There are only two ribs, 8 feet 4 

 inches apart, in each arch, and of a deal and a half (1 foot 4 inches) 

 in width, and ten deals (2 feet 7 inches) in depth. Tlie longitudi- 

 nal beams are half balks of timber, 13| inches by 6j inches. There 

 are two stone abutments, each 40 feet long, and five stone piers. 

 The largest pier is 91 feet high from the foundation, which is 5 feet 

 below the surface. All the piers are 10 feet thick at the springing, 

 12 feet 10 inches wide, and 5 feet 4 inches thick at the top, under- 

 neath the roadway. The total cost was : — masonry, 3,617/. ; car- 

 pentry, 3,358/. ; together, 6,975/., which is a very small amount for 

 a work of such magnitude. 



