Page 62 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

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FABRICATION AND ERECTION*

2.24 CHAPTER TWO

FIGURE 2.9 (Continued)

shown may have either the kangaroo (topping lift) or the hammerhead (horizontal boom) configuration.
Kangaroo and hammerhead type cranes often have moveable counterweights that move back as the load
is boomed out to keep the crane balanced. These cranes are sophisticated and expensive, but are often
economical because they are usually fast and may be the only practical way to bring major building
components to the floor they are needed. Crane time is a key asset on high-rise construction projects.
Jacking is another method used to lift major assemblies. Space frames that can be assembled on
the ground, and suspended spans on bridges that can be assembled on shore, can be economically
put together where there is access and then jacked into their final location. Jacking operations require
specialized equipment, detailing to provide for final connections, and analysis of the behavior of the
structure during the jacking.
For marine installations with adequate water depths, such as bridges over waterways or off-shore
petroleum industry platforms, the magnitude of erecting lifts and reaches increases dramatically.
Floating carriers transport large quantities and/or assemblies (modules) to the site for erection.
Barge- and ship-mounted revolving or shear-leg cranes do the heavy lifting. These cranes are capable
of reaching twice as far with as much as five times as much load as land-bound cranes. Wire-rope
slings used for these lifts are comparably sized and specially configured for handling flexibility.

2.12 ERECTION METHODS FOR BUILDINGS

The determination of how to erect a building depends on many variables that must be studied by
the erection engineer long before steel begins to arrive at the erection site. It is normal and pru-
dent to have this erection planning developed on drawings and in written procedures. Such docu-
ments outline the equipment to be used, methods of supporting the equipment, conditions for use
of the equipment, and sequence of erection. In many areas, such documents are required by law.
The work plan that evolves from them is valuable because it can result in economies in the costly
field work. Special types of structures require extensive planning to ensure stability of the struc-
ture during erection.

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