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 Some issues for the designer to be aware of include:
The rigging and lift may impose loads on a structural assembly which were not anticipated by the
designer. Even if the assembly is not damaged by the lift, it may undergo unexpected
deformations which 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 which
support the major roof elements.
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 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.
Some issues for the designer to be aware of include:
There is the potential for unexpected loads may 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.
Economy of Framing Systems
Hangar geometry is the single most significant factor influencing the efficiency of the structural
system. The long clear span supporting the hangar door head, coupled with large column free
interior spaces, is the factor which distinguishes the hangar structure framing system from most
standard construction. The two most common structural systems large hangars, as typified by
the Type 1 Maintenance Hangar, are the Header Truss and the Cantilevered systems.
Figure 2.3.1.5 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 as well as conjectural facilities, displays trends with which
the designer should become familiar.
The designer is cautioned that the figure is a simplification of the existing background
information. The information presented is based upon the assumption that a standard Type I
Maintenance Hangar is being produced. It has been further assumed that the hangar bay space is
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