To stiffen the standards, short ledgers are tied across as shown in [fig. 27].
PLATE II.
[Photo by W. Cottrell
Hightown, Manchester.]
EXTERNAL CHIMNEY SCAFFOLD.
Erected for the Willesden Electric Lighting Works, under the supervision of E. Willis, Esq., A.M.I.C.E., etc.
When the chimney is to be erected by external scaffolding the ordinary mason’s or bricklayer’s scaffold is used. Owing to the small area of the erection the outside frames of the scaffold have a quick return. This makes it practically impossible for the scaffold to fail by breaking away from the building under the influence of the loads it may carry. Shoring or tying is therefore not so important. Wind pressures have, however, a greater effect, especially when the direction is not at right angles to one of the faces of the scaffold. If in that direction, the tied putlogs would offer resistance. Braces are therefore imperative, and they should be fixed at right angles to each other, each pair thus bracing a portion of the height of the scaffold equal to its width. (See plate 2.)
For the repair of chimney shafts without scaffolding from the ground level, means have to be taken to bring, first the mechanic, and afterwards his material, within reach of the work.
Fig. 27
The preliminary process of kite-flying is now rarely seen, except for square-topped chimneys, and even in these cases the delay that may arise while waiting for a suitable steady wind is a drawback to its practice. The kites used are about 10 feet long and 8 feet wide. They are held at four points by cords which continue for a distance of about 16 feet, and then unite into one. Near this point on the single rope another cord is attached, which serves to manipulate the kite into position.
Stronger ropes or chains are then pulled over the shaft, after which a workman ascends, and the necessary pulley wheels and timbers to form a regular means of ascent are sent up after him.
A light line carried up in the interior of the shaft by a hot-air balloon is another means of communication.