Page 59 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

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FABRICATION AND ERECTION*

FABRICATION AND ERECTION 2.21

FIGURE 2.5 Stiffleg derrick.

Truck cranes can be used with booms up to 500 ft long and have capacities up to 750 tons. Rough-
terrain cranes have hydraulic booms and are also highly mobile. Truck cranes and rough-terrain
cranes have outriggers to provide stability.
A stiffleg derrick (Fig. 2.5) consists of a boom and a vertical mast rigidly supported by two legs.
The two legs are capable of resisting either tensile or compressive forces, hence the name stiffleg.
Stiffleg derricks are extremely versatile in that they can be used in a permanent location as yard der-
ricks or can be movable for use as a traveler in bridge erection. A stiffleg derrick also can be mounted
on a device known as a creeper and thereby lift itself vertically on a structure as it is being
erected. Stiffleg derricks can range from small, 5-ton units to large, 250-ton units, with 80-ft masts
and 180-ft booms.
A guy derrick (Fig. 2.6) is commonly asso-
ciated with the erection of tall multistory build-
ings. It consists of a boom and a vertical mast
supported by wire-rope guys which are attached
to the structure being erected. Although a guy
derrick can be rotated 360°, the rotation is
handicapped by the presence of the guys. To
clear the guys while swinging, the boom must
be shorter than the mast and must be brought up
against the mast. The guy derrick has the advan-
tage of being able to climb vertically (jump)
under its own power, such as illustrated for the
construction of a building in Fig. 2.7. Guy der-
ricks have been used with booms up to 160 ft
long and with capacities up to 250 tons.
Tower cranes in various forms are used
extensively for erection of buildings and
bridges. Several manufacturers offer acces-
sories for converting conventional truck or
crawler cranes into tower cranes. Such a tower
crane (Fig. 2.8) is characterized by a vertical FIGURE 2.6 Guy derrick.

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