By Don McLaughlin, P.E.

Aircraft hangars are commonlyreferred to as "glorified garages" forairplanes. They can vary from simple"shade" structures that protect the air-craft from the elements to complicat-ed, high-tech, environmentally con-trolled maintenance facilities.However, a major cost factor of anyhangar facility is the hangar super-structure itself. Compared to ordinarybuildings addressed by most buildingcodes, the load and serviceabilitydemands placed on the hangar super-structure are unique.

Door OpeningsThe superstructure must contain largedoors that allow aircraft access; there-fore, hangars could be described aslarge buildings with at least one wallmissing. The superstructure mustwithstand all load combinations withthese doors open or closed. The opendoors verses the closed doors usuallyrequire separate wind load analyses.Because of the door openings them-selves, plan stiffness eccentricities are

created that lead to unconventionalload paths. Three-dimensional analy-sis and design techniques are usuallybest suited to handle the stiffnesseccentricities.

The doors themselves can be free-standing, can be bottom supportedand lean on the hangar or actually besupported by the hangar superstruc-ture. The type of door depends on theclimate at the hangar site as well asowner preference for operations. Thetype of door has a major influence onthe hangar superstructure framingsystem.

Serviceability ConstraintsHangars are usually tall, flexiblebuildings but are still only one-storybuildings. Building codes oftenrequire the use of loads that considerthe hangar a multi-story buildingbecause of its height. Design of thehangar long spans and tall heights areusually governed by serviceabilityconstraints and not by member stress-es. Serviceability constraints includelimiting the deflection and sidesway

Aircraft Hangar Superstructure SelectionIdentifying Selection Criteria

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160-meter clear-span aircraft maintenance facility for Evergreen Airways in Taiwan, Republic of China. This structure utilizesa space frame roof system with a lateral load resisting system composed of braced frames.

Each hangar design is unique

in that client needs, local

building codes, site con-

straints, material availability

and the availability of a

trained work force are driving

factors in the selection of a

structural system.

Structural SolutionsIn pursuit of cost-effective solutionsfor long-span hangar design, manyconcepts for aircraft hangar super-structures have been studied anddeveloped. Some major structuretypes that have been studied include:

• Rigid Frame Conventional SteelFraming

• Braced Frame Conventional SteelFraming

• Space Frame Construction• Three-hinged Steel Arches• Splayed Steel Arches• Cantilever Trusses• Suspended Trusses• Pretensioned Steel Structures• Post-tensioned Steel Structures• Fabric Roof Structures• Concrete Shell Structures• Numerous Proprietary Systems

As in most engineering solutions, themost cost-effective solution for onesystem does not necessarily translateinto the best solution for all the sys-tems of the project. For example, anefficient hangar superstructure mayresult in higher overall costs for themechanical/electrical systems andhigher operating costs over the life ofthe facility.

Cost-Benefit AnalysisGenerally, it is best to minimize theexterior surface of the hangar andconsequently the volume of thehangar. The smaller the hangar exteri-or surface area, the less siding, roofingand insulation that will be requiredand the smaller the magnitude of thewindload that must be resisted. Bydecreasing the volume of the hangar,

there are cost savings in mechanical,electrical and fire protection systemsboth initially and in operating costsover the life of the hangar facility.

This cost benefit must be weighed rel-ative to the hangar’s smaller size andsuitability for a specific aircraft.Finally, the benefits and costs of eachsuperstructure system should be stud-ied in conjunction with life-cycle costsof the other systems and presented tothe client for selection of a structuralsystem.

Don McLaughlin, P.E., isstructural manager for Burns &McDonnell's Aviation andArchitecture Group. He wasrecently selected by the NationalInstitute of Building Sciences toauthor a design guide for air-craft hangars. He has bachelor'sand master's degrees in civilengineering from the Universityof Missouri, and is a licensedprofessional engineer in 12states.

of the hangar so that the doors remainoperational under certain load combi-nations.

Typically, hangar facilities also havespace for offices, maintenance shops,warehouses and utility areas. Thesespaces are generally adjacent to thehangar space and "lean" on the hangarsuperstructure. Typically the columnsin this space are closer together andthe multi-story areas feature stiff con-crete slabs. Therefore, this space isstructurally stiffer than the flexiblehangar space, which must be takeninto account during design. Again,three dimensional analysis and designis usually the best solution for han-dling the different stiffnesses.

Unique RequirementsEach hangar design is unique in thatclient needs, local building codes, siteconstraints, material availability andthe availability of a trained work forceare driving factors in the selection of astructural system. Other major factorsthat may affect the superstructureinclude:

• Airport clear zone requirements• Type and number of aircraft• Preference for positioning the air-

craft in the hangar area• Preferred hangar door type, config-

uration, and clear opening require-ments

• Categories of maintenance to be per-formed

• Requirements for suspended workdocks, telescoping cranes and over-head bridge cranes

• Weight of suspended mechanicaland electrical equipment

• Roofing material and roof sloperequirements

• Future expansion of the facility