At the building of the new Post Office, Leeds, 1893, a different method of raising the platform for the crane was adopted. The legs, instead of being framed, consisted of a single balk of timber strutted on each side from the ground level, the sleepers and guys being firmly attached to the standards themselves.
When erecting long ranges of buildings it may be more convenient to have the derrick mounted upon a travelling bogie than to dismantle the structure in order to re-erect at another point.
[Fig. 6] illustrates the system, the travelling power being usually manual. The arrangement is suitable for small derricks, and is employed where the crane is erected outside the building.
Fig. 6.—Showing Staging mounted on Travelling Bogie
Another method of using travelling cranes is to erect a platform as shown in [fig. 7].
The standards, which may be of balk timber or built up, as previously shown, are about 10 feet apart longitudinally and 20 to 30 feet transversely. They stand upon sills of the same section where the foundation is not solid. On the head of the standards, the runners are laid connecting all the standards in the same row.
Head pieces may be fitted between the standards and runners; this serves to distribute pressure. All the connections are securely made by dog irons, bolts, and straps. The stability depends entirely upon the bracing, and this, it is important to note, should be between each bay longitudinally, and at least every second bay transversely.
Fig. 7.—Elevation of Derrick Staging