How Is Long-Span Aircraft Hangar Structure Really Engineered?

Hangar structures are engineered with long-span roof systems (trusses or rigid frames) designed for deflection-controlled performance, lateral systems that work around the open door wall, and foundations sized for the large column reactions. The open side makes the lateral load path the critical design challenge. The design philosophy is that the clear span is the easy part to draw and the hard part to make work. Anyone can sketch a 250-foot truss; engineering it means controlling deflection, detailing the connections for the real forces, and giving the lateral loads a complete path to the ground with one wall missing.

Roof diaphragm design is the unsung hero of hangar engineering. With the door wall open, the roof deck is the element that collects wind and seismic forces and delivers them to the braced walls — and at 200+ foot spans, the diaphragm forces are large. The deck attachment, the diaphragm connections to the frames, and the drag struts all have to be designed for those forces. A roof that's strong in gravity but weak as a diaphragm is a hangar waiting to rack. Connection design at this scale is its own discipline. The truss-to-column connections carry enormous forces, the splices in 250-foot trusses have to be detailed for erection as well as service, and the base connections have to handle the frame moments. I detail hangar connections for the forces the analysis actually produces — including the erection-stage forces, because a truss that's fine in service can be vulnerable halfway through erection.

Long-span structures forgive nothing. The priorities below are what I design to on every hangar frame.

• Design for deflection: serviceability and door operation govern member sizing at long spans
• Engineer the diaphragm: roof deck, attachments, and drag struts as the lateral system's backbone
• Detail the connections: truss splices, frame knees, and bases for real forces including erection
• Design both door conditions: lateral systems verified with doors open and doors closed
• Found for the reactions: large concentrated loads with settlement control for doors and rails