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Steel Shots: Raising the Roof with Enhanced HSS

The 200-ft, tri-chord roof truss system for the new Seattle North Transfer Station uses 90 tons of ASTM A1085 hollow structural sections (HSS), produced by Atlas Tube (an AISC Member). This is the largest use of these HSS on the West Coast of the U.S. (Photo courtesy of Atlas Tube)

Seattle’s new North Transfer Station is tipping the curve toward enhanced hollow structural sections (HSS) with the use of the new ASTM A1085 specification for the tri-chord roof trusses within the station’s 57,000-sq.-ft tipping and transfer building  — the largest use of these HSS on the West Coast of the U.S.

These trusses, which have a depth of six feet and a maximum span of 200 feet, optimize the floor space for a free flow of trucks entering and leaving the building. In the north-south direction, the roof trusses will also be used as the primary lateral system, while steel trusses at the southwest corner will be used as the transfer system to support the floor framing and lateral braced frames. In total, nearly 1,600 total pieces of round HSS with a weight of 3.25 pounds per square feet were produced by Atlas Tube (an AISC Member) for the 11-chord roof trusses. The tighter tolerances of ASTM A1085 HSS (as compared to ASTM A500) allowed the engineers to design using the full wall thickness of material. This resulted in a more efficient design overall.

The transfer station uses 1,170 tons of structural steel in total, which was fabricated and erected by Fought & Company in Tigard, Ore. (an AISC Member and Certified fabricator). In addition to the tipping and transfer building, the station will have a 10,000-sq.-ft  reuse/recycling building and a 2,500-sq.-ft administration building. It is set to open this year and replace an outdated station that was on the site. The goal will be to recycle about 750 tons of solid waste, organic material and recyclables every day.


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