Page:The Building News and Engineering Journal, Volume 22, 1872.djvu/217

 Marcu 8, 1879. THE BUILDING NEWS. 201 and curves‘round to the right with a radius of fifteen chains tillit reaches Dalston Junction, and at this point the eastern branch forks off with a curve of 10 chains radius, and joins the main line at a point about 20 chains from the western junction. The eastern branch is constructed for two lines of rails only; the western branch and the main line were made originally for three lines of rails as far as Worship-street, and from this point to Broad- street there were four or more lines of rail. With the exception of the curves at Dalston Junction there is no curve on the line less than 20 chains radius. The total length of the main (City) line is 4,060 yards, or rather more than two and a quarter miles. The length of the eastern branch is 600 yards. The steepest gradient on the line is 1 in 60. The line commences in cutting about 20ft. deep, and passes under the Kingsland-road and Dalston-lane by means of cast-iron bridges or rather galleries. The catting between retaining walls is continued as far as Grange-road, and from this point to Acton-street it is carried on an embankment be- tween retaining walls. From Acton-street to Broad-street it is wholly constructed on arches, and at the various street and road crossings is carried over either by cast-iron or wrought-iron bridges. At Forest-road and Fox-lane it was necessary to carry the line under the former and over the latter ina comparatively short length—21 chains only; hence the gradient of 1 in 60 was introduced, which, although then thought to be objectionzble, in practice is found not so. Mr. Lawford said that he was not aware that in the construction of the line any new engineering feature calling for special remark was introduced. He would, there- fore, merely describe one or two of the iron bridges, which would give a fair notion of the bulk of them. There are altogether twenty cast-iron bridges and seventeen wrought-iron bridges. The former consist of longitudinal girders with small segmental brick arches between them. The latter are of two sorts: (1) those consisting of two main box girders, with transverse plate girders, and (2) longitudinal girders only from the smaller span bridges. In both sorts of wrought-iron bridges the flooring con- sists of bent plates fin. thick. There was nothing novel in the construction of the retaining walls for the cuttings and embankments. Those in the cuttings have stood perfectly, but in the embank- ment a short length has failed, owing, as Mr. Lawford conceived, to the constant heavy traffic so close to them from the 45-ton tank locomotives, the weight of which has been increased from 42 tons since the line was opened. With regard to the arching of the viaduct, the spans varied from 25ft. to 32ft., according to the lengths of ground between street and street. The arches were all segmental, the versed sines being 6ft., 6ft. 6in., and 7ft., according to spans. ‘The piers averaged 5ft. in thickness, and the arches were 2ft. thick. These latter were all well coated with #in. of asphalte, and were thoroughly watertight. The cast-iron bridges varied in span from 20ft, to 32ft., @.e., for carrying the railway, whilst those for carrying the roads are nearly all 36ft. span. Mr. Lawford said he knew that many engineers objected to so great a span as 32ft. in a cast-iron girder, but if the girders were well made and properly tested, he thought that span, but no more, might be adopted as a safe maximum span for cast-iron girders carrying the railway. He had built many railway bridges of that span, and had never yet known any single girder fail. For streets, too, when the span did not exceed 32ft., and when there is much traffic, the cast-iron girder with brick arching offered some advantages, foremost among which were the absence of vibration from passing trains, and the consequent freedom from noise underneath, and the greater facility for making the flooring watertight, and thus preventing the rain from soaking through and dripping on to the passers-by underneath. Thedimensions of the 32ft. cast-iron girders in the centre were:—Depth of girder, 2ft. 9in.; width of bottom flange, 2ft. ; of top flange, 7in.; thickness of bottom flange, 2‘in. ; area, 66 square inches; thickness of top, 1Jin.; centre web, 2in. at bottom, and 1Jin. at top; both top and bottom flanges the same width throughout ; the depth at the end was 2ft. 3in.; camber of girder, 2in. The dimensions of the smaller span cast-iron bridges were in the same proportion as those above quoted. In no case was there less than 2ft. bearing at each end. The cast-iron girders of the road- bridges were 36ft. span, and 40ft. over all; depth in centre, 2ft., and at the ends, 1ft. Sin. ; section of bottom flange, 1ft. 10in. x 2uin., giving an area of 55 square inches ; camber, 24in. The total number of cast-iron girders used on this line was 340, every one of which was thoroughly examined and tested before it was allowed to be used. Nearly all were tested to half their breaking weight. The breaking load that could possibly come on one girder was 25 weight of a 32ft. girder was 140 tons in the centre, or 280 tons over all,*and as the greatest moving tons, and the permanent load was 43 tons, the Board of Trade regulations were strictly adhered to— i.¢., six times the moving load (25 x 6) = 150 tons plus three times the permanent load (48, x 3) = 129; total, 279 tons. Thus up to a 32ft. span, Mr. Lawford said he believed that for many reasons a cast-iron girder was the best. He did not say the most economical, for he thought the increased_ weight of cast-iron metal more than counterbalanced the higher price of wrought iron. He thought, too, that where the span admitted of its being used, that cast iron was more lasting and durable than wrought iron for girders, and most cer- tainly the brick arch between the girders made a better flooring than either bent or buckle plates. Cast iron, too, retained the paint much better than wrought iron, and his experience was that if paint did rub off cast-iron girders, a sort of skin formed over the metal, which stopped any further deterioration from rust, &c. The brick abutments of the bridges on the line were all made on the same type—#.e., with pockets. Some of them were very irregular in shape, owing to the very skew angles at which the roads crossed, but in no case was there less than 6ft. Gin. width of brickwork at the smaller end of the triangular-shaped abutments. The largest wrought-iron bridge on the line is that over the Kingsland-road, near the Shoreditch Station. The height is 16ft.* clear headway above the road, and so sharp was the angle at which it crossed the road, that although the width of the road at that part was only 42ft., the span of the main girders was 122ft. This bridge consisted of two main or box girders, and forty-one transverse girders, the latter yarying in length from 5ft. to 40ft. This was occasioned by the line crossing the road at such a sharp angle, and fromits being curved over the bridge. The minimum width of the line (three lines of rails) is 36ft. between parapets. The two box girders are 10ft. high between the top and bottom flanges. The width of the top flange is 2ft. llin., that of the bottom flange 3ft. The top table, as shown by section in the centre of the girder, consists of one din. plate, four gin. plates, and four angle irons din. X 5in. x 3in., giving a total area of 115 square inches. The bottom table con- sists of five 2in. plates, and angle irons same as in top table, giving a total area (exclusive of angle irons) of 90 square inches. The rivets are Zin. diameter and 4in, pitch. This section of the girder is 69ft. long. The remaining lengths of the girder, 16ft. and 17ft. on both sides of the centre, have re- spectively one and two plates less than the central portion; this applies both to the top and bottom members. The transverse girders of this bridge consist of five sorts. A description of the longest (40ft.) wovld be a correct description of all the other transverse wrought-iron girders on the line:—Depth, 2ft. Gin.; width, 1ft. 4din.; top table, two plates, each nine-sixteenths of an { inch thick ; bottom table, two in. plates ; din. packing strip Zin. wide, and two angle irons 3}in. x 3in. x tin., both top and bottom. The two next sizes of tranverse girders (all, it is to be observed, being of the same depth—viz., 2ft. 6in.) were 1ft. 2in. and 1ft. wide respectively, both having two top and bottom jin. plates. The next girder was only 10in. wide, and had one tin. plate top and bottom, and the smallest consisted simply of two angle irons for top and bottom flanges, the centre web of all these transverse girders being +in. plate. The side plates of the girders are respectively +in., five-sixteenths of aninch, and in. in thickness, The butt ends of all plates, angle irons, &c., were planed perfectly true and smooth, and the whole of the rivet holes were drilled. The flooring consisted of bent plates fin. thick, rivetted on to springing)plates zin. thick, running over the tranverse girders the whole length of the bridge, and on which plates longitudinal timbers for carryingrails were laid. With the exception of these bridge crossings the whole line was laid on transverse sleepers. The next longest bridge on the line is that over Regent’s Canal and Dunston-road. Practically it is one bridge divided into two spans by means of a couple of cast-iron columns, the span over the canal being 78ft. long,and that over the road 59ft. long. It is com- posed of two main box girders and transverse girders 4ft. Gin. apart from centre to centre. It was so precisely similar in all respects to the bridge over the Kingsland-road (making due allowance in the sections of the main girders for the lesser span), that it need not be further described. It was the best looking bridge on the line; it was built on a flat angle, but seen from a short distance looked square. Expansion and contraction in these large bridges was provided for by cast-iron plates, planed perfectly true and even, under both ends of the main girders. The other description of wrought= iron bridge alluded to was applied to those roads where the span did not exceed 45ft., and consisted of plain plate-iron longitudinal girders. Each bridge had six girders, carrying the three lines of railway, and two outside girders for the parapets. The section of the carrying girders was :—Depth, 2ft. 9in.; width, 1ft. 8in.; top tables, two din. plates; bottom tables, two plates, each nine- sixteenths of an inch thick; }in. packing strip, 74in, wide; and two angle irons, 33in. x 3gin. X gin. in both members, the central web being qin. thick. The flooring was precisely similar to that already mentioned—yiz., bent plates din. thick. In connection with this part of his subject, Mr. Lawford asked whether it was not possible, in wrought-iron bridges, to get rid of two- things, both of which were a great nuisance—viz. (1) the noise from the trains overhead, and (2) the constant dripping of the rain in wet weather. Both evils, he thought, might be very much modified, but he doubted if anything short of roofing over the entire structure of a wrought-iron bridge, and 10ft. or 15ft. beyond at each end, would ever even keep the roads underneath quite dry. One of these wrought- iron bridges he did manage to keep dry for a long time, but eventually it leaked. He believed, however, he could have improved upon that plan, and was going to apply it to a second bridge, when he was peremptorily stopped by a lawyer's letter, telling him he was infringing a patent, and threatening pro- ceedings if he ventured to goon with it. His plan, which came to so untimely an end, was simply to asphalte well the whole of the tops of the girders and bent plates, then to lay a thickness of well- tarred hair-felt over the whole, and then to asphalte that again. For eight or ten months that mode was quite effectual in keeping out the wet. Another question which he should like to hear discussed, although it was one more for the traffic manager than for the engineer, was as to the policy that led railway directors, and notably those of the North London Railway, to adopt three lines of rails. In this case they had seen their mistake in not haying originally constructed this short branch for four lines of rails, and by their short-sighted policy they had incurred an extra expense of at least £100,000. rails; but a fresh Act of Parliament was necessary, a fresh contract for works, fresh conveyances for land, &e., et hoe genus omne—all of which means money. The London and North Western Railway Company, a few years ago, pursued the same course —i.e, they put down a third line of rails from Bletchley to London, on the east or up side. Now they are putting down the fourth line on the west side. Why? Because they find it is impossible to. work a heavy and frequent traffic safely on three lines of rails. (To be concluded.) id ARCHITECTURAL & ARCHAOLOGICAL SOCIETIES. LiverrpooL ARCHITECTURAL AND ARCH#O- LOGICAL Soctery.—The eighth meeting of this session was held at the Royal Institution, on Wednesday last. A paper was read by the President on ‘‘ Hints from the Lives of Eminent Architects” ; also a paper by the Secretary on ‘*‘How to Deal with Densely Populated Districts.” Oxrorp ARCHITECTURAL AND HisTORICAL. Socrery.—The first evening meeting this term was held, by permission of the Keeper, in the large room at the Ashmolean Museum, on Tuesday week. The President of the Society occupied the chair. Mr. J. P. Earwaker, of Merton College, one of the secre- taries, then gave an account of some archxological discoveries during the past year in the neighbour- hood. He observed that a large portion of the far- famed Dorchester Dykes had been wantonly removed by the present owner of the estate. Referring to the remains of the Roman villa at Northleigh, he said that a short time since a memorial was drawn up calling the attention of the Duke of Marlborough to its bad state of preservation. Atfter waiting several months, and receiving no reply from his Grace, mention was made of it at the annual meeting in November last. He sent a letter on the subject to the Oxford Journal, and this was copied by several of the London papers. The Duke saw the letter, and it appeared that the memorial never reached him. The Duke had, however, since been furnished with a copy of it, and had expressed his willingness that a further investigation should take place, both in this and the Roman villa at Stonesfield. He had also had the tesselated pavement at Northleigh well pro- tected from the weather. Mr. Earwaker produced a
 * The line was now being widened for a fourth line of