UFC 4-211-01N
25 October 2004
Once completed, the entire element is lifted into place and the final support
connections made. Fabricating on the ground allows for enhanced safety for the
bulk of the work as well as greater control of quality and ease of access for
inspectors. The drawbacks of the approach include the cost associated with
mobilizing a crane or cranes that can lift the assembly. Tight quality control is
essential to ensure that the final fit is made.
4-5.5.1.1
Some issues for the designer to be aware of include: The rigging
and lift may impose loads on a structural assembly that were not anticipated by
the designer. Even if the assembly is not damaged by the lift, it may undergo
unexpected deformations that may then be locked into the final structure once
the last connections are made. The heavy lift may place the large, overhead
elements into place prior to the remainder of the facility's framing being
completed. This is often a physical requirement given the necessity of getting
equipment adjacent to the lift operations. The designer should give some
consideration early in the design as to the lateral stability of the building
components that support the major roof elements.
4-5.6
Aerial Assembly with Shoring Towers. This approach is
becoming increasingly uncommon with the general availability of large cranes
and the increased emphasis on avoiding fall injuries on the work site. The
approach involves the fabrication of temporary towers to support the piece-by-
piece fabrication of the major components in their final place. The temporary
shoring towers location will determine the actual deflected shape of the structure
resulting from the dead load of the structural steel only.
4-5.6.1
Advantages. The advantage of aerial assembly is that it avoids
the necessity of having a large capacity crane and fabrication errors may be
discovered and corrected without postponing a single milestone-lifting event.
The disadvantage of the aerial assembly is the loss of productivity and potential
for accidents related to high work.
4-5.6.2
Issues. Some issues for the designer to be aware of include:
There is the potential for unexpected loads to be introduced in the
structural framing system by poorly designed shoring towers or long
term settlement of the shoring towers.
The manner in which the temporary towers are removed may also
introduce unexpected, albeit temporary, loads in the main structure.
4-5.7
Economy of Framing Systems. Figure 4-1 is presented to
provide planning guidance for the structural steel requirements in a Type I
hangar and in selecting a primary structural system. The figure, developed from
the review of recently designed facilities, displays trends with which the designer
should become familiar.
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