334 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[October, 



plained by the di.igram were for 15 feet bearings, 12 in. deep in tlie 

 centre, and 8 in. at tlie ends, and 1 J in. thick in the centre ; the forked 

 or divided parts were each U tl"'^k, and the roll at the top 2i in. 

 diameter. They were proved to 20 tons by 13 tons in the centre, 

 although there is not a probability of their having to carry 9 tons, but 

 the object was to give confidence to the public; the deflexion was an 

 inch. The skew-backs were cast hollow, having stiffening pieces 

 about 3 ft. apart, as shown by the plan and section. 



Between the girders arches were turned in half a brick in cement, 

 care being taken in setting out the work to bring in the courses with 

 very close joints, and so as for the bricks to touch each other at the 

 lower side ; the 5 or G centre courses were put in without cement, so 

 as to get jammed in tight, after which they were grouted. The rise 

 of the arch was 5 inches, the spandrils were not filled in, and the 

 bricks were well snaked in water. 



The centreing was in all cases held up or suspended to the girders 

 by iron hangers, whereby the weight was gradually placed upon it; 

 this would not have been the case if the centreing had been put up on 

 props and afterwards struck in the common way. 



About 22,000 feet of these arches have been turned, and not the 

 slightest appearance of a settlement is to be found in any part of them. 

 The floors over the arches are formed in the usual manner, with joists 

 and sleepers. The iiitrados are plastered, and a soffit with papier 

 mache work is fixed to the underside of the girders to conceal them. 



The reliance to be placed on this method of building as a security 

 against the extension of fire from room to room, has been fully tested 

 in the following manner ; a large coke fire was made in the centre of 

 each room on the basement floor (which is only 8 feet high) in order 

 to dry the plastering, &c., and although the heat was kept up intensely 

 strong on many successive days, yet it had no worse effect than to 

 make the floor boards, in only two cases out of eighteen, of the rooms 

 over, swell a little so as to be barely perceptible, and that was evi- 

 dently caused by the quantity of steam driven through from the wet 

 plastering of the arches and walls below. 



I am. Sir, 



30, Guildford Street, Your obedient servant, 



September 2, 1842. Charles Dter. 



NOTES ON THE CONSTRUCTION OF BRIDGES. 

 Description of Sunderland Iron Bridge, nilh remarks on its construction, and ishy it has not been more adopted. 



In the " Notes on the Construction of Iron Bridges" in your July 

 number, among other matters noticed, it is contended that no advan- 

 tage is gained in confining the principal weight of iron in the arch at 

 the bottom, over the equal distribution of the metal in the arch, the 

 spandril filling and roadway bearer, and that the great elasticity of 

 wrought iron renders it inapplicable to the purposes of bridge 

 building. The former remark is fully confirmed, and the latter obvi- 

 ated by a combination of the two materials, as in Sunderland Bridge, 

 a sketch of which accompanies this paper, and which for sake of 

 brevity, and as distinction of its construction, I will name the 

 Vertebrated Bridge, the wrought iron bands being like the spinal 

 chord, and the short portions of the arc of cast iron framework 

 being the bones. When it is considered that in each of these ribs, 

 there is a sectional area of 134 superficial inches of wrought iron 

 employed, whose power of resistance to comjiression is within an 

 eighth of being twice as much as cast iron, the utility of this mode of 

 construction over that wholly of cast iron must be self-evident, and 

 moreover, the time since the erection of the bridge under consider- 

 ation proves its practical durability.* 



Should the system of a combination of the two materials be fully 

 carried out, by making the bars of wrought iron radiate from the 



* 'the use of wrought iron in connexion with bridgenork, is shown in Mr. 

 Brunei's arch, described iu Journal, vol. 1, 1838, page 119, which contained 

 no less than 54 pieces of hoop iron, 1 inch broad, by -rj thick, interspersed 

 between the joints. 



crown of the arch so as to fill up the whole of the spandril, as in the 

 case with the filling in of the spandril of Chepstow Bridge (a plate of 

 which is given in Weale's Bridges), I have no doubt of the feasibility 

 of extending an arch of this description to the extent of 500 feet, an 

 extent proposed by Telford for the bridge over the Menai Straits, 

 or of 000 feet, as proposed over the Thames by the same engineer. 



Mr. Rennie's experiment on Southwark Bridge (see Journal, vol. 3, 

 1840, page 133) proves that the dilation and contraction of the metal 

 is no impediment, being in that structure only -^ of an inch for an 

 alteration of temperature of 1° of Fahrenheit, and the whole contraction 

 of iron from a fluid to a solid state being yij as stated by Mr. 

 Edwards, in his account of the Pont du Carrousel in Journal, for 

 last August, page 279. 



I must now return to the subject at the head of the paper, and 

 commence with its history. So early as 1790, Rowland Burdon Esq.^ 

 conceived the idea of throwing an arch of cast iron over the Wear, 

 at Sunderland, for whicli purpose an Act of Parliament was obtained 

 in 1792. The foundation stone was laid September 24th, 1793, and 

 the bridge opened August, 1796. The quantity of iron in the struc- 

 ture is 260 tons, of which 46 tons are wrought iron. The novelty of 

 the plan adopted on the suggestion of Mr. Burdon, consisted in 

 retaining, with the use of a metallic material, the usual form and 

 principle of the stone arch, by the subdivision of the iron into blocks, 

 answering to the stone of the common arch. These blocks. Figs. 1 and 2^ 

 are of cast iron, 5 feet in depth and 4 inches in thickness ; each block haa 



