TRANSACTIONS OF THE SECTIONS. 151 



stronger, and cheaper principle than the timber framing heretofore 

 used in this country. 



For this purpose the author exhibited models on a large scale of the 

 peculiar ' lamination' of the timber in the arches, by which, along 

 with other advantages, a decided advantage is gained in strength. 



With a model upon this principle for a bridge across the Tyne 

 120 feet span, experiments were made in the presence of part of the 

 managing directors of the railway, and some scientific persons, which 

 proved highly satisfactory; for a weight of 250 stone was placed 

 upon it, without the slightest deflexion of the arch being perceptible. 

 This, multiplied by 144, accoi-ding to the scale of the model, gives 

 34,900 stone, or upwards of 218 tons, as the weightthe arch of 120 feet 

 would bear without being aifected. A great surplus strength was 

 therefore manifest, to cover all contingencies, and make allowances for 

 the increased span and extra dimensions. 



The plans and elevations of two viaducts at Ouseburn and Willing- 

 ton Dean were laid before the section. The former, at the eastern 

 suburb of Newcastle, is 920 feet in length and 108 feet in height ; there 

 are five arches, of 1 16 feet span each, and two stone arches, at each end, 

 of 45 feet span each. These were introduced in order to prevent the 

 mounds coming too close upon the very steep banks of the ravine. 

 The latter bridge is 1150 feet long, and consists of seven arches, 120 

 feet span each. The height up to the roadway is 82 feet. Stone 

 arches were not requisite here, as the banks are of a more gradual 

 slope. 



The piers and abutments are of stone. Each arm is composed of 

 three ribs, formed to the proportionate curve shown on the model. 

 Every rib is put together with 3-inch deck deals, in lengths of from 

 20 to 45 feet, and two of the deals in width. The first course is 

 formed of two whole deals in width, and the next of one whole and two 

 half deals ; and so on alternately until the whole rib is formed. Each 

 rib consists of 15 deals in height or thickness, and the ends are butted 

 one against the other, breaking joint, so that no two of the horizontal 

 or radiating joints shall come together. The whole are connected with 

 oak trenails or pins, each of which passes through three of the deals in 

 thickness. Between every deal a layer of brown paper, dipped in boiling 

 tar, is laid, to secure the joints from being affected by wet, and so as to 

 make the timbers bed tightly one upon the other. The ends of each 

 rib are inserted into large cast iron shoes or sockets, which are first fixed 

 to the springing stones of the masonry, and secured with long iron bolts, 

 four to each plate, run in with lead. The three ribs are connected 

 together with diagonal braces and iron bolts. 



The spandrils, formed by the arches, being great, on account of the 

 span, the framing is made in proportionate strength. A beam 

 14 inches square is fixed about the middle of the spandril, inclining 

 upwards to the crown of the arch ; from which struts are carried, both 

 above and below it. Those above are perpendicular to the longitudi- 

 nal beams of tiie roadway, and those below are radiating to the centre 

 of the arch. 



