Castings play key role in new roof at Arthur Ashe Stadium: Cast Connex and Bradken combined to produce a key connection for the renovation of a famous tennis arena.
For two weeks every year, Arthur Ashe Stadium is the center of the tennis world. Located in Queens, New York, it serves as the main arena for the Open, hosting the biggest matches in one of the planet's most important tournaments. Tens of thousands of ticket-buying spectators and millions more in a worldwide television audience see the stadium as it welcomes international stars like Serena Williams, Roger Federer and Novak Djokovic.
But currently, Arthur Ashe Stadium is undergoing a major renovation that will dramatically change its look and feel. It's a renovation with massive and noticeable aspects, but also one made up of less-noticed but equally important phases.
Completed in 1997, the stadium was built without a roof. Because of this, matches were susceptible to the elements and the tournament schedule was often altered because of delays and cancellations. To fight the elements, the U.S.Tennis Association (USTA), the body that owns and operates the facility, announced in 2013 it was adding a retractable roof to the arena, following the lead of fellow major venues for Wimbledon and the Australian Open.
That roof, at a cost of a reported $150 million, is structurally independent from the stadium itself and is expected to be operational by the 2016 event in late August. The hulking steel frame was already in place for last year's tournament, missing the polytetrafluoroethylene fiberglass membranes that will eventually cover the roof and provide protection when inclement weather hits.
Of course, the project is much more complicated than simply slapping a roof structure over an existing arena. The new structure is supported by eight steel columns spaced around the perimeter of the stadium that are joined to ground-level concrete piers. Each base is a point where two diagonal braces are connected to a vertical steel column by cast steel connections. As fans walk into the arena, they stride right past the connections that are in place to help keep the roof up.
Enter Cast Connex, Toronto, and eventually its chosen partner for the project: Bradken, Kansas City, Missouri.
Around February 2014, Cast Connex, a supplier of castings and forgings with engineering and design capabilities, was contacted by steel fabricator Canam Group (SaintGeorges, Quebec, Canada). After a 2014 request from the New York City Design Commission, the USTA and the outside builders were tasked with creating the connections for the structure base that were strong and also attractive, since they are visible to spectators entering the arena.
Cast Connex was asked to deliver a custom-designed product, with the connections and braces in place by November 2014.
"From a structural perspective, the entire weight and lateral system of the roof goes through these connections," said Carlos de Oliveira, principal, Cast Connex. "The connections are also important from an architectural perspective, given that these connections are the only location where spectators can interact directly with the new roof structure."
According to de Oliveira, each of the connections weighs around 7,700 lbs. (3,492.7 kg) and connects to 30-in. (76.2 cm) diameter steel braces on one end. On the other, they're welded to the 40-in. (101.6 cm) diameter columns.
"They're at the interface between the very large diameter bracing and columns," de Oliveira said. "The casting I transitions from the round brace down to a relatively thin vertical plate, providing an organically shaped transition between the two geometries."
The Connections' Role Is Key
As de Oliveira alluded to, the components need to do more than look good.
"The components are structural; they each support a large portion of the weight of the roof. And when the wind blows on the structure, they have to transmit the resulting lateral forces down into the foundations," de Oliveira said. "And if there was ever an earthquake, the inertial forces caused by the excitation of the structure would also be transmitted through the cast steel connections.
"As such, these are absolutely critical structural components."
Cast Connex is not a casting facility. It designs the cast steel structural components for the construction of buildings and bridges, and partners with steel facilities for the manufacture of the components it designs.
Cast Connex has designed critical components for many other largescale projects like the architecturally exposed cast steel nodes for the Transbay Transit Center project in San Francisco. The company offers a variety of standardized components, like universal pin connectors, that are used in a wide range of buildings, including the Whitney Museum of American Art in New York.
"From an architectural perspective, we can create geometries and connections that offer very different aesthetics than one could achieve by fabricating connections from welded platework," de Oliveira said.
Metalcasting also brings structural advantages as well, like a smooth force transfer between different shapes.
"Ultimately, we can put the material where it ought to be for the flow of forces through the structural component, rather than trying to build up or stiffen platework. We literally shape the part as nature would shape it," de Oliveira said. "When you do that, you often end up with something that looks very elegant. So we leverage the geometric freedom that casting offers to improve structural performance and also to improve the aesthetic quality of connections."
In the Ashe project, Cast Connex turned to Bradken and its Atchison, Kansas, facility for tooling, casting production and machining. The two companies had worked together in the past, and based on their strong professional relationship and the size and complexity of the part, Bradken was the right facility for Cast Connex.
"It's increasingly difficult to have those relationships today when so many people try to commoditize an engineered component," said Wayne Braun, director of business development --industrial products, Bradken. "The value added to that relationship put forward co-designing the component to yield the best results and lowest cost of quality."
The components were cast via the nobake sand casting process utilizing a 50 ksi grade of steel casting to an ASTM A958 specification, which is one of a number of standard grades for the structural market.
The two companies used a collaborative relationship to produce the connections. There was feedback, give-and-take, input, and evidence of a strong professional relationship.
"Not everybody can do this because there are a lot of technical and quality back-and-forth between the two because of the importance of these components, not only the structural integrity but also the expectation visually," Braun said. "In addition, the precision needs to be put in the weld-prep areas so that these castings fit into the plane. This allows them to be fabricated in position without creating potential dimensional issues at the fabricator when he goes to do fit-up."
Braun said "getting off on the right foot" was important for the project. The metalcaster didn't want to get far along and find out the finished component did not match expectations. Representatives of different parts of the project's chain were invited to see the castings and provide feedback.
"Getting that first article done and understanding that you've laid the part out properly, and have machined it within the plane is why we do the 3-D overlay," Braun said. "Or we'll lay it out and then send them the file, and they will then put it in the envelope to make sure that it complies. Once you've got that locked down, then you can be sure your subsequent parts are going to yield the precision that's required in the dimensional component."
Other manufacturing processes theoretically could have been used to create this component. Casting, however, brought many distinct advantages. Beyond the aesthetics, it holds an ability to handle a bigger range of challenges, not to mention the absence of weld joints, leading to more capability to handle stresses.
"One of the advantages is the ability to make shapes that are aesthetically pleasing to an architect," Braun said. "If you combine those with the various grades and strengths that steel offers in addition to its weldability, it really gives you a number of options that allow you to cast shapes that are extraordinarily difficult or almost impossible to fabricate."
Projects like these have another advantage: it can help a firm like Bradken continue to make its mark in the architectural world. Bradken is a member of the American Institute of Steel Construction, and Braun and de Oliviera have given co-talks on the use of steel castings and the benefits they can bring.
"We can say not only do we believe this, we're actually doing it and we've done it in this example, this example and this example," Braun said. "You don't want somebody who's never done one before that says 'Yeah, I think we can cast that shape,' because it's about understanding what you're casting, why you're casting and what's important on that casting."
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|Article Type:||Cover story|
|Date:||Mar 1, 2016|
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