Page:Forth Bridge (1890).djvu/47

Rh sides were put together and drilled, as also a mass of small detail work, and all the temporary girders used in the erection and in the stagings.

Outside these workshops and the drill-roads, many acres of ground were taken up with the building up and fitting together of the various girders, of which the single booms had been drilled in No. 1 shed. Thus a great portion of the internal viaduct was put together and a number of bracings which had to be templated in the first instance in situ, were done and multiplied. These portions of the internal viaduct were erected for one pair only, however, and in the others it was simply repeated.

The bottom junctions, or junctions between bottom members, struts and ties and wind-bracings in cantilevers, were laid down and finished on the drill-roads, while those of the top members with struts and ties were laid down and built in tho field.

For the handling of the plates, beams, and other parts of the tubular members and the skewbacks and bottom junctions, powerful travelling cranes (see Fig. 75), some with curved jibs 40 ft. high, were used, and these could move about all over the drill-roads, being shifted from one line of rails to another by means of traversers. Ordinary derrick cranes worked by steam or by hand were also largely used.

In the shops, however, most of this work was done by hydraulic cranes of very simple construction, yet eminently adapted for their work. (See Figs. 84 and 85.) In many places they were so disposed that material could be lifted and swung round from one to the other so as to traverse the whole length and breadth of the shop. (See Fig. 76.)

A large amount of rivetting was done in the yards and the field in the case of such portions of the girders as the booms of the tension members, and later on, whole portions of the rectangular wind-bracing girders, of which then the joints only required rivetting up after they were erected. Much rivetting was also done upon the longitudinal beams and the diaphragms in the tubular members. All this rivetting was done by hydraulic machines, and could be finished at an extremely cheap rate.

The work in both No. 1 and No. 2 sheds, and on the drill-roads, was carried on day and night, though the number of men was much greater during the day-time. The working hours were from 6 a.m. till 5.15 p.m., and from 5.45 p.m. until 5.45 a.m. for night shift. No deduction was made for meal hours during the night, the full twelve hours being paid for. When necessary the work in the field was also carried on during the night.

The total output of work from all these places has amounted to as much as 1800 tons in a month, which is a very large quantity when it is considered through how many hands every piece was required to pass before it could be called finished.

The lower or fixed bedplates, in size about 37 ft. long by 17 ft. wide, are built up of five layers of plates, the lowest $3/4$ in. in thickness, the second $1 1/4$ in., and the third and fourth 1 in., alternately laid longitudinally and transversely, to obtain distribution of fibre in all directions. The fifth layer consists simply of a band, 11 in. wide and $1/2$ in. thick, laid round the edges of the bedplate, partly as a stiffener, partly as a means of retaining the lubricating medium between the lower and upper bedplates. Immediately under the vertical column a recess is formed by cutting out of the two upper 1-in. plates a space varying in form, but in all cases for the purpose of admitting a keyplate of similar form, a portion of which is rivetted to and forms part of the upper bedplate.

The bedplate as above described was put together on a carefully-prepared bed in No. 1 shed, clamped and fastened down securely, and a traveller with several boring spindles passed over the whole of the plate, drilling all holes through the various thicknesses at once.

All holes were $1 1/8$ in. in diameter, and countersunk both top and bottom. The forty-eight holes 3 in. in diameter for the holding-down bolts were drilled in the same place, but by a specially constructed tool described above, and the plate was then taken to pieces and stowed away until wanted.

As soon as the granite piers were ready for the reception of the bedplates they were put together at a height of about 4 ft. above the masonry, and supported for the time being on short pieces of bolts, coupled to the foundation bolts by long nuts and in other places by pieces of cast-iron piping of equal length. The rivetting machine was then placed at one end, and the rivetting commenced. (See Figs. 86 and 87.) The machine consisted of two strong box-plate girders, carried on two side-frames moving on wheels, and kept apart vertically a sufficient distance to admit the bedplate, with a rivetting cylinder attached to the upper and another to the lower girder. The cylinders could by screw movement be moved from one end of the girders to the other, and thus commanded the whole width of the bedplate, while for forward or backward movement the side-wheels had to be pinched. The two cylinders were turned on simultaneously by one valve. The cylinders were 12 in. in diameter, and the water pressure 1000 lb. per square inch. The pressure upon the rivet and the plates was, therefore, about 40 tons from each cylinder. The rivets had a countersunk head at one end, and flat snaps were used on both cylinders. The rivets were heated in an ordinary brick furnace placed on the pier, and brought to a full yellow heat. There were 3778 rivets in each of these bedplates, which gives for the area of 654 square feet about six rivets per square foot.

As soon as the machine had moved away a yard or so from the end of the plate, chippers were set to work to pare down the projecting piece on each rivet-head on the under side of the bedplate, in order to have this perfectly even and flush.

After the men got into the way of properly using the rivetting machine, these bedplates were rivetted up in twenty-eight hours, or 135 rivets struck per hour, which is very creditable work, considering the size of the rivets and that so much shifting of the machine and of the supports for the bedplate had to be done.

After all the rivet-heads had been chipped, the bedplate was lowered into its place by hydraulic rams. Two thicknesses of canvas, one laid in the length, the other in the breadth of the plate, both being well soaked in and painted over with red lead, were interposed between the cement bed described above (see granite piers) and the plate to