Walker Art Center Structural Engineering
Minneapolis, MinnesotaChallenge
Designed by the Swiss architectural firm of Herzog %26 de Meuron, the expansion of the Walker Art Center in downtown Minneapolis embodies art with its cantilevered box forms, large frameless windows that wrap around corners, and sloped and folded walls, ceilings, and floors. The architectural concept envisioned the largest box cantilevering more than 40 feet beyond a glass wall, without permitting columns along more than half of the perimeter. The space between boxes defined a civic space - a town square - connected to exterior gardens and terraces through glass walls. The architectural design required the glass to be butt glazed and as open as possible to merge interior and exterior spaces. Columns placed behind the glass walls to support the roofs and elevated public terraces would have disrupted the continuity.
Solution
Structural engineers HGA devised highly innovative solutions to the architectural challenges. The dramatic theater cantilever is possible through the use of wall trusses that wrap three sides of the box. Two 60-foot-deep wall trusses cantilever approximately 60 feet past their single support column to suspend the massive form above the sidewalk. The glass walls remain unobstructed by columns, as structural steel mullions support the roof. By post-tensioning the anchor bolts to achieve base fixity and loading each with just a single roof beam, the required section could be made as small as a mullion designed only for wind. The mullions are formed from welded steel plates and milled to tolerances one-fourth that of typical steel.
Photography %A9 Paul Warchol