Page:Forth Bridge (1890).djvu/69

Rh In all cases mentioned here the wire rope had a higher breaking stress than the other two.

Facility of attachment was also a very good feature; for they could be tied like an ordinary rope, or else have the end fixed round a common thimble or deadeye, and be used with shackles. Nearly all the small stages which had been passed up and down or along the members were hung by short pennants made of wire rope.

Finally, they could be slung alongside or across the structure, and by means of running snatch-blocks every place made accessible to the men, or they could be used for raising material by means of single whips worked over a steam-winch barrel. The employment of wire ropes for this purpose is well shown in the large illustration on Plate X. and Plate XV.

The sizes used here mainly were the 2$1/4$ in. or $7/8$ in. diameter, the 2$1/4$ in. or $3/4$ in. diameter, and the 1$7/8$ in. or $5/8$ in. diameter were used on cranes or for single whips upon steam winches. For special purposes 3$1/4$-in. and 4-in. ropes were used, and for the service of men's cages and hoists the 3 in. or 1 in. diameter. The tests for the latter gave a breaking stress of 26 tons to 28 tons, while nothing heavier than 3 tons in the case of material and 35 cwt. in the case of a cage full of men were ever put upon them.

The internal viaduct has already been fully described in connection with the structure. The four rail-troughs in which the double line is laid are 18 in. in depth by 16 in. in width. (Fig. 155.) They are asphalted in the bottom to the level of the heel in the angle-bars, in order to make a water-tight bottom. Upon this bottom are laid transversely, about every 2 ft. 8 in. apart, blocks of teak about 5 in. square. Between these blocks the spaces are filled in with blocks of creosoted pine, all set about $1/8$ in. to $1/4$ in. apart, and the whole is then filled up to level with a mixture of pitch and tar and black oil, which quickly sets hard.

Stiffening plates of steel, about 6 in. wide and $3/8$ in. thick, are rivetted in about every 14 ft., and project about 2 in. above the teak blocks. All blocks are cut with an inward slope towards the centre of each line of about $1/2$ in. to the foot.

The whole mass of blocks and filling, which completely seals the lower portion of the trough, are now dressed for the reception of the longitudinal sleepers, which are about 12 in. by 5$1/2$ in., and also of teakwood. They are cut in lengths which are multiples of the 2 ft. 8 in. distance of the transverse blocks, and are notched where the plate-stiffeners occur. Play to the extent of $3/16$ in. to $1/4$ in. is left between sleepers lengthwise.

Through the sleepers holes are bored every 2 ft. or 3 ft., and $3/4$in. pins driven down into the blocks. The sleepers are kept in position transversely by wedge-shaped blocks of teakwood. The upper faces of the long sleepers are dressed to receive the rails of " bridge" section, the heaviest yet rolled weighing 120 lb. to the lineal yard. A section of the rail is shown in Fig. 156. The rails are joined by a horizontal fish-plate underlying the flanges, and sunk into the sleepers with a projection entering into the hollow of the rail. The rails are screwed down by $3/4$in. wood screws with hexagon heads. The total weight of rails, fish-plates, bolts, expansion joints, &c., for the double line of rails across the bridge and viaducts, is over 600 tons.

The rail-troughs are drained of water through holes drilled into the sides every few feet at the level of the top of the tranverse [sic] blocking. In the floor of buckle-plates between the four troughs holes are placed to let the water through, these spaces being made up with asphalt mixture in such manner as to lead all the water to the outlets. Tho footpaths on each side of the double line are made up like ordinary pavements, on the system followed by the Seyssel Asphalt Company, the slope being such as to lead all water to the outer sides.

These are all arranged on the same principle, though of different lengths. In the approach viaduct span, and at the fixed ends of the central girders, the movements are so insignificant that a very short rail-joint suffices to regulate the lateral displacement of the points due to contraction; but, at the sliding ends of the central girders, where provision is made for a longitudinal movement of two feet, and at the ends of the fixed cantilevers, where half that length is provided, the arrangement is somewhat more complicated. Without going more into detail, it will suffice to say that the long rail-tongue is made an absolute fixture to the rail-trough in which its uncut end rests. Its pointed end, cut at an angle of 1 in 63, projects into the opposite trough and rests on a plate fixed therein, laying up close to the backing rail, which is bent away at an angle of 1 in 63 from the point of the tongue. The outside of the flange of the rail-tongue is cut in long steps at the same angle of 1 in 63, and is held down by draw-washers to the plate, which forms one piece with the backing-rail, but in such manner that it can slide in and out with the expansion and contraction. In doing so, however, by means of the sloping steps it draws the lower plate and with it the backing-rail always close up to the joint, which thus retains its position relative to the centre line of the bridge and thus keeps the gauge correct. The contrivance is very ingenious and unfailing in its action. (See Fig. 127.) The wind fence on each side of the viaduct is 4 ft. 6 in. high, and of close lattice work, and it is crowned by a handsome teak handrail of substantial appearance.

All plates, bars, angles, and other parts belonging to the superstructure, received as soon as they had passed through the shops or yards a thorough scraping with steel scrapers and steel wire brushes, and afterwards a coat of boiled linseed oil applied as hot as possible. As soon after erection upon the structure as could conveniently be done, and in many cases also before they were put up, they received a coat of red lead paint, and subsequently a second coat of red lead. The paint finally decided upon for the bridge is an oxide of iron paint, of which two coats are applied over the two coats of red lead already laid. The first is called a priming coat of dark chocolate brown ; the last is a finishing coat of a bright Indian or Persian red, which, however, darkens considerably in a short time. Four different kinds of paint are used, all, however, of the same composition, if of different makers.

At Fife: Craig and Rose's.

At Inchgarvie: Galley's Torbay.

At Queensferry : Carson's.

For central girders: Wolston's Torbay.

The above are for outside painting only, the inside of the tubular members receiving one coat of red and two coats of white lead paint. It is calculated that inside and out, the amount of surface to be painted is equal to 145 acres.

The batter given to the sides of the structure brings with it one disadvantage, namely, that one-half of each lattice-girder flange forms with the vertical web a recess in which rain-water can lie and cause rusting. To prevent this, all places so situated that the water cannot of its own accord drain away are tilled with asphalt-concrete—that is, a mixture of asphalt, pitch, tar, and coarse gravel—to such an extent that all water will run off by gravity. Where this is not possible, or would lead to too much weight being put on, holes are drilled, and the asphalt so laid that the water is drained to them and away through them. The top members in central towers, all horizontal bracing girders, and all recesses in top and bottom junctions, are done in this way.

The whole of the inside of the skewbacks, except where the nuts of the foundation-bolts are situated, are also dealt with in the same manner, and the same at the bottoms of the vertical columns, the diagonal columns, and the struts in cantilevers; and in all cases pipes are fixed to lead the water to the outside. By this means it is hoped to prevent all rusting in the places where access for constant and thorough inspection, is not easily to be had.

Taking them as a whole, it must be freely acknowledged that the workmen employed upon the bridge have not, to any material extent, added to the troubles and anxieties attendant upon such a work. Black sheep are found everywhere, and of the doings of such a tolerably lively account might easily be presented. Many of them hundreds of them were mere birds of passage, who arrived on the tramp, worked for a week or two, and passed on again to other parts, bringing a pair of hands with them and taking them away again, and having in the mean time made extremely little use of them except for the purpose of lifting the Saturday pay packet and wiping their mouths at the pothouse; many others also, who, too clean-shaven and too closely-cropped as to hair, vainly tried to deceive any one as to the character of the hotel they were last staying at, or to invent a plausible account of the big job which they had just left completed. The paddle-steamer, which carried the men across the river morning and night, during the day made hourly trips to the north shore and back for the service of the works and for the accommodation of visitors. Before many months had gone by it waa known all over the country to every tramp that a free passage could be had for the stepping on board the boat, and the number of men who, when on tho south side, were invariably asking for a job on tho north side, and vice vend, increased at such an alarming rate that steps had to be taken to stop the nuisance.

But apart from these, it is no exaggeration to say that no one need desire to have to do with a more civil or well-behaved lot of men, always ready to oblige, always ready to go where they were told to go, cheerfully obeying orders to change from one place to another, and, above all things, ready to help others in misfortune, not with advice but with hands and purses. Nor was there any difference in that respect on account of nationality; Scotch, English, and Irish were about equally represented as to numbers, and though the latter furnished very few skilled hands, they were mostly very hard workers and very conscientious and reliable men.

For the sinking of the caissons a number of foreign workmen were employed for a short time, and it is rather a curious coincidence that, as foreign workmen did some of the earliest work in connection with the bridge, so now again a number of foreign men are employed upon some of the last work—namely, the laying of the asphalt pavement along the footpaths of the permanent way, which is done under a sub-contract by the Seyssel Asphalt Company.

Several strikes occurred during the building of the bridge, most of them brought about, not by the men themselves, but by organised committees in connection with various Trades Unions and their disputes with employers in other parts of Scotland. The causes were often trivial enough, such as the discharge from the works of some idle scamp with an inordinate allowance of the gift of the gab, and whose demand to be reinstated in his dignity at twenty-two shillings per week, caused an immense amount of useless suffering to scores of his fellow-workmen, and more still to their families, and a proportionate increase in the takings of the neighbouring whisky shops.

The principal strike took place early in June, 1887, and was brought about through an accident, caused entirely by the carelessness of a few men. A movable stage for rivetters, consisting of two girders about 110 ft. long, disposed on either side of the vertical columns, was hung by wire ropes from winches worked by worm and wormwheel placed above. The stage served for rivetting the wind-bracings between the columns, and was made good by planking across the two girders in any place required. When one section had been done the stage was raised to the next section, and while