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Cast Connex innovative cast steel use in San Francisco project

Don Procter

Through the innovative use of cast steel, a Toronto-based steel designer/supplier is participating in a mega transit terminal set to rise in downtown San Francisco.

The company, Cast Connex Corporation, is designing more than 70 unique cast steel elements, ranging in weight from 5,000 to 45,000 pounds for the planned Transbay Transit Center, a six-block integrated transit hub that will dwarf Toronto’s Union Station and New York’s Grand Central Station when it is completed later this decade, says Carlos de Oliveira, president of Cast Connex.

The one million square foot regional transportation hub will feature over 300 castings with a combined weight of 3.4-million pounds, says de Oliveira.

Steel castings play a critical role “in enabling the unique structural system and achieving the lofty architectural intent — without which the architectural expression the design team was aiming to achieve could not have been realized,” he says.

The Transbay Transit Center is the largest steel castings contract in the building construction market in North America and possibly in the world, he says.

The steel castings comprise part of a steel “tree-like structure” that makes up the podium around the six-block terminal.

The rising tubular steel structure is made up of basket columns — named for the inclined steel columns which support the undulating bubble-shaped glass façade wrapping the perimeter, de Oliveira points out.

The cast nodes at the ground floor join massive transfer girders under the substructure to the basket columns. Those columns bifurcate (spread out) at the bus deck level where more cast nodes are specified. At the roof cast nodes connect the basket columns to the soffit of the spandrel beams, he explains.

De Oliveira says the spandrel beams and tree-like basket columns form an eccentrically braced frame designed for maximum seismic resistance.

“In an earthquake these trees comprised of large steel pipes and nodes have to remain predominately elastic and allow for yielding of the eccentrically braced link beam that is part of the spandrel at the roof level.”

The stringent seismic requirements and unique design dictated the use of the modified eccentrically braced frame. The steel castings are integral to that frame and specially detailed true-pinned joints at some of the cast node connections allow for frame movement in an earthquake, he says.

Manufacturing the steel castings will have to start soon, he points out, because all of the cast nodes are to be delivered before the end of 2014. It is expected that several steel foundries will be required to complete all of the castings on time.

The project’s architects are internationally renowned Pelli Clarke Pelli Architects and Adamson Associates International. Adamson’s head office is in Toronto. Structural engineer is Thornton Tomasetti.

While steel castings are only now gaining more widespread use in North America, in Europe and Asia cast steel nodes and steel castings are and have been commonly specified for decades.

De Oliveira reasons that cast steel is still novel in Canada and the U.S. partly because steel manufacturing and casting design isn’t covered indepth in university civil engineering programs.

“Structural engineers here often associate steel castings with cast iron and that they are brittle. That’s not the case.”

De Oliveira believes that projects like the huge transit centre will raise the profile of castings in North America.

Cast Connex is a products/technology company which developed several standardized cast steel components, some designed in-house, others through research at the University of Toronto where de Oliveira and colleague Michael Gray learned “everything there is know about castings and applied it to building construction.”

The pair co-founded Cast Connex in 2007. The company is also involved in two major New York City projects: the World Trade Center Tower 3 with Rogers Stirk Harbour + Partners and the new Whitney Museum of American Art, a design by architect Renzo Piano.

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