Quantcast Additional Cantilever Requirements

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Thermal Loads
The designer must account for anticipated differential thermal effects from solar heating (e.g., on
long sun-exposed exterior steel compared to shaded steel such as roof trusses, joists or decking)
or inside/outside differences (particularly an "attic" effect in the hangar bay). The designer
should consider local climate conditions when selecting the final differential temperature range,
as a minimum, a temperature differential of  28C ( 50F) should be used for design. Particular
attention should be paid to the deflections caused by thermal effects. Some architectural facia
elements and weather seals around hangar doors are particularly vulnerable to detrimental
deflections. These thermal effects are a serviceability concern and as such should be
investigated using unfactored loads.
Additional Cantilever Requirements
The cantilever truss roof design should incorporate a deflection primary and secondary
adjustment method. The design drawings and specifications should require the Contractor to
"level" the truss tips (above the hangar door) after all roof and supported materials have been
installed into their final positions. It is suggested that the primary adjustment system be installed
in the forestay (and the backstay if necessary), but other systems are permissible. To level the
truss tips, the Contractor should be required to survey the roof truss system to ensure the
structural system is performing as the designer intended. The Contractor's survey should be
done during stable atmospheric conditions (night, early morning, or a cloudy calm day). The
designer of record should review and approve the survey information prior to installing the
hangar doors. Primary adjustments of more than 25 mm (1 inch) vertical movement, if required
to level the truss, should be approved by the designer of record. Secondary or cosmetic
adjustments up to 25 mm (1 inch) of correction can be accomplished by shimming or milling
structural members below the truss tip under the supervision of the Contracting Officer.
Additional Main Framing Design Requirements
Main hangar structural systems should include a system for adjusting the truss connection should
temperature extremes be encountered at the time of erection. A statement as to the allowable
temperature range within which the erection may proceed without adjustment should be stated in
the construction documents. Typically, the unadjusted temperature range should be 20C 11C
(68F 20F), however the designer must verify the allowable temperature range on a case by
case basis.
Hangar Doors
Hangar door guide systems are normally sized to allow total roof truss live load deflection not to
exceed 200 mm (8 inches). The designer of record should be responsible for coordinating the
total anticipated roof deflection with several potential door guide manufacturers to ensure that an
economical system may be selected.
Static Determinacy
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