Engineering Wonders of the World
Volume I

332 ENGINEERING WONDERS OF THE WORLD. DIAGRAM TO SHOW HOW THE CANTILEVER ARMS WERE BUILT OUT. performed in as many strokes with the rams, th© ends of the platform being raised alter- Lifting a Platform. nately. After each stroke the beams immediately support- ing the cross girders were pinned in position, and the press girders released and raised by admitting water above the pistons. Then they were pinned in turn and the others released. This operation had to be repeated sixteen times during a lift. Encircling the columns, below the platform, to which they were attached, were the cylin- drical riveting cages, covered in with wire netting to prevent the fall of men, tools, or rivets, etc. At each cage one gang worked outside the tube, another inside. Similar cages were used on the tower struts and the lower booms of the cantilevers. As the columns were free at the top during construction, their own incli- Correcting nation from the vertical, the , *he . weight of the platforms, and Inclination , . , of the wind pressure caused seri- Columns. ous deflections, which had to be corrected from time to time by means of wire ropes for pulling inwards and timber struts and hydraulic presses for thrusting apart. Such correction was a delicate operation requiring the greatest care, and, as the columns were terribly stiff, the use of enormous power. Half-way up a halt was made to build in the crossings of the diagonal struts in the centre of the tower. A crossing contains, in the case of Inchgarvie, 80 The tons of steel on each Elevation side of the tower. reached When they and the horizontal bracings were finished, the platforms resumed their upward jour- ney to the top—reached at a height of 360 feet above high water, practically identical with that of St. Paul’s Cathe- draL They there almost touched one another, having drawn closer and closer as they rose. The gap was covered over so as to form one large platform of more than double width, and the longitudinal girders were stiffened with heavy chains to prepare for the con- struction of the lattice-work horizontal ties connecting the column summits. These ties were soon put together and joined to the top skewbacks, from which, as from their larger brethren beneath, members run in many BUILDING OUT A LOWER BOOM. RIVETING CAGE STARTING ON ITS JOURNEY.