August I, 1878] 



NATURE 



367 



occur during the operation. For the different sizes of 

 girders, different jettys and pontoons were used, but apart 

 from this the operation was carried on in the same manner 

 in all cases. But here again it soon became clear that 

 while to carry out the smaller ones in doubtful weather 

 was a dangerous operation, the larger ones were far less 

 liable to disturbance by the weather, and some of them in 

 fact were subjected to a severe trial in this respect, the 

 two tu£;s on one occasion being unable to tow the structure 

 in the ordinary manner against the strong westerly wind, 

 and breaking all the tow ropes. As soon, however, as 

 additional towing power had been procured, the operation 

 was successfully carried through. Intricate as it seemed 

 to build these heavy girders on shore and tow them to 

 their destination— often more than a mile distant — ^by the 

 use of plant specially designed for the purpose, the exe- 

 cution became very easy, it seldom taking more than 

 twenty minutes to convey them from the one place to the 

 other. 



Lifting the Girders to their Permanent Resting Places. 



The general arrangement of the six columns which 

 have to support the larger spans follows that of the brick 

 piers on which they rest Four centre columns placed in 

 a square and connected by strong vertical and diagonal 

 bracing, are 15 inches in diameter, and from these 

 centre columns the lifting of the span takes place. Each 

 of the columns is about 10 feet long, varying slightly 

 according to the height of the pier, and every second 

 length has brackets cast on to which transverse girders 

 are bolted. The outside columns placed on the point 

 of the pier are 18 inches diameter, and as well as the 

 inside ones i inch thick. Between these outside and inside 

 columns rest the ends of the main girders, the end cross 

 girder and end horizontal bracing having been left out so 

 as not to come in the way of the four central columns and 

 their bracings during the process of lifting. To each 

 vertical end post a T strip is bolted from top to bottom 

 in the same manner as was described for the large 

 caissons. In common with these it has 3J inch holes at 1 2 

 inches distance. A transverse trough girder of slightly 

 shorter length than the distance between these end posts 

 is placed on the temporary girders connecting the columns, 

 and in this two hydraulic rams, carrying another girder 

 are fastened. By inserting steel pins in the holes nearest 

 to this top girder, and then pumping up, the main span 

 can be raised to such a height as the stroke of the rams 

 will permit, and if at that point pins are put in the holes 

 then nearest to the fixed or lower ram girder and the 

 weight allowed to come down upon these, the rams can 

 be lowered again without letting the main girders down, 

 and by a shifting of the pins to a lower hole, the opera- 

 tion can be repeated, each stroke of the rams causing 

 a rise of the girders of i foot. The motive power is 

 derived from a pump worked by manual labour, the space 

 at disposal not permitting the introduction of steam- 

 power for this purpose. The diameter of the pump-plungers 

 must therefore be small, and the movement of the rams 

 consequently a slow one. It was, however, possible to 

 lift 20 feet a day, and during the long days of summer a 

 40- feet lift has often been reached in 24 hours. Another 

 set of apparatus was kept in readiness on the next Hfting 

 girder, and with it operations were continued, when the 

 girder had become too high for the lower ones, which 

 then in their turn were shifted to a higher point. As the 

 girder rose, the bracings connecting the outer columns 

 with the four central ones were put in, and after it had 

 reached its final height a system of girders capable of 

 carrying the bed plates and superstructure were fastened 

 on the top of the columns, and the girder which had 

 been elevated to a few inches above its proper height was 

 lowered down on them. Before this could, however, be 

 done, they had to be connected to the next set of girders, 

 as they were calculated as continuous girders and joined ' 



together in sets of four. To make these junctions, one of the 

 ends had to be hfted up from 5 to 6^ inches, while the junc- 

 tion plates making the top and bottom booms continuous 

 were riveted on. The lowering of the girder at the other 

 end would then produce an initial strain in these junctions 

 and fulfil the requirements of continuity. A good deal of 

 time v/as required for making these junctions, the junction- 

 plates having all to be carefully marked and drilled while 

 the girders were still hanging in the apparatus, and this 

 circumstance in one case led to a disaster which caused 

 great loss and delay. On February 3, 1877, while the 

 work of joining the two southmost of the 245 feet spans 

 was in preparation, a gale of unprecedented severity came 

 down the valley of the Tay with such a fierceness and 

 suddenness that it was even impossible to get near enough 

 to the piers to take off the men who had been at work on 

 them, and they were obliged to seek shelter on one of the 

 adjacent girders which had not been raised. The wind 

 continuing to blow in strong gusts produced violent 

 vibrations in the unbraced ends of the girders and 

 gradually shifted them to the edge of the lifting girders^ 

 causing one side to fall when the limit of stability was 

 reached, breaking down the pier and precipitating the 

 other girder in consequence. The fallen girders had to 

 be lifted, cut up, and replaced by new ones, and the work 

 was thereby materially delayed. 



Lifting of the 145 Spans. 



The lifting of the 145 spans was accomplished in a 

 somewhat different manner. The hydraulic lifting appa- 

 ratus was placed on the top of a temporary structure 

 of timber fixed on the cast-iron piers, a few feet higher 

 than the top boom of the girder would be after being 

 raised, and long links with holes a foot apart reached to 

 where the girder stood 5 feet above high water. These 

 girders being so much lighter could be raised to the top 

 in one day, but as the arrangement of the columns was 

 somewhat different from that of the 245 feet piers (the 

 girders resting on the four central columns), they were 

 hoisted while fixed together by temporary transverse 

 bracings, which kept them at a greater distance apart than 

 they would finally be, and hoisting them up outside the 

 columns altogether. It was therefore necessary to 

 modify the apparatus to this extent that the girders, 

 after disconnecting the temporary bracing, could be slung 

 in and permanently braced. 



The work in connection with this bridge was begun in 

 the summer of 187 1, the first stone of the land pier on 

 the south side being laid on July 22 of that year. 

 During the first three years, however, little progress was 

 made, and the operations during that time must be con- 

 sidered as being more of an experimental nature. From 

 August, 1875, however, the progress was very great, 

 and as the managers and men gained experience, the 

 erection of the structure was proceeded with at a vastly 

 accelerated rate. New workshops, jetties, and appliances 

 of various kinds were added, a foundry erected for the 

 casting of columns, and in September, 1876, it was found 

 necessary, in order to keep pace with the building of piers 

 and erecting of girders on shore, to work night and day, 

 and the contractor introduced for the first time in Scot- 

 land electric light for out-door work. Two lamps, each 

 of 1,000 candle-power, the current for which was generated 

 by Gramme machines, did excellent service. The lamps 

 were placed at right angles to each other, and in this 

 manner they lit up an area of 100 by 500 yards in suck 

 a way that every kind of work could be carried on unin- 

 terruptedly. This was of great importance for the floating 

 out of piers and girders which had to be done at high 

 water, the preparations commencing three or four hours 

 beforehand, and therefore having sometimes to be made 

 in the early morning. The last pier was in this manner 

 floated out at seven o'clock on the morning of December 

 26, 1876. 



