North Transfer Station Rebuild, Tipping, and Transfer Building, Seattle. Photo: Integrated Design Engineers
ers the building and most of the remaining site. The varying angles and porosity of the canopy infill members filter and reflect sunlight. Struc- tural steel was the best material to meet this architectural challenge. A set of irregularly shaped one- and two-story pavilions — providing gallery, studio, community, administrative, and service space — have concrete fill on metal deck diaphragms supported by steel beams and girders, with steel columns bearing on spread footings and grade beams. Steel framing efficiently supported the long-span roofs over large gal- leries and could be manipulated to address complicated skewed condi- tions, sloping and intersecting roofs, and various cantilevered regions. Buckling-restrained braced frames (BRBFs) serve as the lateral force- resisting system in the pavilions. The canopy is supported by round hollow structural sections (HSS) of varying diameters ranging in height from 15 feet to 35 feet, all supporting HSS14x10 girders and beams. They, in turn, support triangular, perforated aluminum infill beams of varying spacing, orientations, and perforations. The canopy columns are each founded on a concrete drilled pier, creating a “flag pole” system of cantilevered columns. The canopy is tied to the building pavilions, so lateral forces are shared by the cantilever columns and the BRBFs,
and the canopy girders function as seismic collectors. Structural analy- sis used RAM Structural System for gravity design of the composite framing of the building and a SAP 2000 model that included both the building and the canopy for dynamic analyses of wind and seismic loading. Structural engineer is Rutherford + Chekene, San Francisco. Consultants include Degenkolb Engineers, San Francisco; Front, Inc., Brooklyn, N.Y.; and WSP | Parsons Brinckerhoff, San Francisco. Merit Award: Apple Union Square, San Francisco — The addition of a new structure over a functioning below-ground ballroom and loading dock that serve the neighboring hotel required creative solutions for the existing building alterations as well as for the new structure. The new alterations are intricately woven into the existing structural fabric. The project comprises three volumes above ground — the store, the bar building, and the plaza. The unique features of the store — including tall sliding doors, a bridge-scale transfer truss, a grand cantilevered floor, a voluminous interior space, and ductile seismic bracing — were all made possible because of structural steel. A significant portion of the steel frame was constructed of wide-flange shapes, HSS, and built-
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csengineermag.com
june 2018
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