Struts from the building below the needles to their outer end, give greater strength to the beam.
When erecting needle scaffolding around buildings of small area, say of a tower or chimney shaft, the needles can be laid across the building in one length, piercing the wall on opposite sides. In these cases, if the needles are wedged in, the weight of the building and the scaffold itself on the opposite ends of the needles, is sufficient to maintain equilibrium.
Fig. 26.—Needle Scaffold
The platform is formed of 9-in. by 3-in. deals, and on this is erected whatever scaffolding may be necessary.
Scaffolds for Chimney Shafts, Towers, and Steeples.—The erection of chimney shafts can be carried on entirely by the aid of internal scaffolding. As the work rises putlogs are laid across the shaft, the ends being well built into the wall. On the putlogs the platform is laid, being carried up as the work proceeds. The putlogs may be left in for the time, and struck on completion. The platform is fitted in its centre with a hinged flap door through which the material is hoisted as required.
There is some objection to this method of scaffolding where the wall is more than 1 foot 101⁄2 inches thick (which is the greatest depth of brickwork over which a man can reach and do finished work), for the mechanics, in order to reach the outside joints, have to kneel on the freshly laid material, which is detrimental to good workmanship. For this reason the system of carrying up an ordinary pole scaffold externally until the height is reached where the wall is reduced to 1 foot 101⁄2 inches in thickness, is to be preferred.
The walls of a chimney shaft decrease in thickness 41⁄2 inches at a time, forming an internal set-back of that width at every 20 feet in height.
This set-back is of advantage to internal scaffolding when the full height of the brickwork is reached, and the cap has to be fixed. The cap or coping, when of stone or iron, does not admit of the insertion of putlogs. To overcome the difficulty, four or more standards are erected at equal distances, and standing upon the top set-back ([fig. 27]).
The standards project sufficiently to carry the pulley wheel well above the total height of the chimney, in order to give head room and to assist the workman in fixing the coping.