December 8, 2015
Category: Structural Bearings, Case Studies - Published by: Émilie Hudon et Pierre Lapalme
The National Football League (NFL) team in Atlanta, Georgia—the Falcons—will have a new home for the start of the 2017 season. The 71,000-seat stadium will have a steel roof structure designed, fabricated, and erected by the Canam-Heavy business unit, with bearings designed and manufactured by Goodco Z-Tech, a product of Canam-Bridges. This represents one of the largest contracts to date for the Canam Group.
The stadium’s roof structure is formed of a network of steel trusses and eight retractable panels meeting at a raised central oculus. When open, the eight panels form an opening of approximately the same area as the football field they overlook. Although Goodco Z-Tech mostly designs and manufactures bearings for bridges and viaducts, in special cases their products are used in buildings.
Goodco Z-Tech will provide 65 pot bearings to support the steel roof trusses, along with several other bearings of various types. The pot bearings are designed to transfer vertical loads and rotation on the three main axes. These bearings can be:
To resist uplift loads, a special device with a centre bolt is used. Unlike uplift restraint systems that are based on steel-on-steel contact, Goodco Z-Tech’s pot bearings with uplift restraint allow rotation and movement, even under uplift loads.
Projects of this magnitude always present great challenges. The stadium’s tight construction schedule, the large quantity of bearings , and the massive weight of the structure make this project particularly complex.
The pot bearings most commonly used in bridge and viaduct construction can resist compressive loads from 2,000 to 10,000 kN, and are seldom subject to uplift loads. On large bridges, compressive loads can reach 20,000 kN. For the new stadium in Atlanta, the highest loads to withstand are 32,000 kN in compression and 10,000 kN in uplift, with many bearings subject to uplift loads of over 5,000 kN. The bearings are also required to withstand rotation and uplift simultaneously. To withstand a compression load of 32,000 kN, the confined elastomer disk inside the bearing is over one metre in diameter.
Another unique characteristic of this project is the orientation of the multidirectional and guided bearings. To allow movement, the bearings are designed with a sliding interface that has a very low coefficient of friction. This interface consists of a PTFE surface recessed in the bearing and located under a larger stainless steel surface with a mirror finish. This is the typical arrangement in the vast majority of situations, as it protects the stainless steel surface from debris, water, and dust. This is particularly important under a bridge, because the bearings are only partially protected from the elements. When bearings are protected from the elements (as is the case here) and the constraints of the structure require to invert the orientation of the bearing, an additional skirt system is supplied with the bearings to protect the stainless steel surface.
To transfer the loads from the bearings to the giant concrete columns that form the structure of the new stadium, base plates were designed by Canam-Heavy and fabricated at the Canam Group shop in Laval, Quebec. A shear key formed by H-beam sections up to W360x990 (W14x665 imperial) (ASTM A992 Grade 50 steel – was welded to the base plates, which measured up to 254 mm (10”). These H-beams have 71.9 mm (2-13/16”) webs and 115 mm (4.5”) flanges.
Confined elastomeric bearings are typically used to transfer loads, movement and rotation from a bridge deck to piers or abutments, but may also be used for special building projects. The roof of the new Atlanta stadium will retract around a central oculus the size of the football field, creating very large compressive (32,000 kN) and uplift loads (10,000 kN), as well as movements and rotations at the bearings. As all Goodco Z-Tech bearings are custom-designed and custom-made, “super-bearings” with new features were developed for certain very large uplift loads. Working in close collaboration, the Canam-Heavy and Goodco Z‑Tech engineering teams came up with optimal solutions to design, fabricate, and erect the roof of the new Atlanta stadium. The technical expertise developed over the course of this project can be used when designing our range of bearings, allowing us to offer our customers the best possible solutions.
Should you have any questions regarding this article, contact us.
Owners: Georgia World Congress Center Authority
Engineers: Buro Happold/Hoberman
Metal components: Canam-Heavy
Structural bearings: Goodco Z-Tech, a product of Canam-Bridges
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