McCarthy Builders Defy Gravity
The Dee and Charles Wyly Theatre – one of the world's most innovative theatres – will have glass walls on three sides, allowing pedestrian views into the working operations of the theatre. With no interior columns, the architecture and engineering teams designed the entire structure of the Wyly Theatre to be supported by six perimeter concrete “super columns” and a concrete shear wall, creating an unprecedented level of openness for a theatre to the outside environment and a structural conundrum. The six perimeter columns are neither at the corners of the structure nor vertical.
Designed by REX/OMA, Joshua Prince-Ramus (partner in charge) and Pritzker Prize-winning architect Rem Koolhaas and engineered by Magnusson Klemencic Associates, the structure is being built by McCarthy Building Cos. With a footprint only 130 feet square, the 12-level Wyly Theatre will feature an unprecedented “stacked” design – a vertically organized facility that completely rethinks the traditional arrangement of a theatre's parts. Unlike a typical theatre building, where support spaces wrap around the stage house, this unique design positions transitional, technical and work zones either above or below the auditorium. This arrangement enables a highly flexible performance space. The facility's advanced mechanized “superfly” system can pull up both scenery and seating, allowing artistic directors to rapidly change the venue to a wide array of configurations.
The primary structure is six cast-in-place battered columns. All the rest of the steel beams visible during the early stages of construction are temporary supports.
“Basically, what we are doing is propping the building up until it is completed,” said Jeff Wagner, project manager for McCarthy. “When it is completed, we'll remove those temporary props and let the building come down and bear its weight on the concrete columns.”
Although the concrete in the columns is rated at 8,000 psi – not unusual for a commercial high rise – their steel reinforcement gives them added strength. Each column contains 21 No. 11 pieces of rebar, supplied by Arrowhead Rebar. TXI is supplying the concrete.
“The building had to be supported until the columns were 100 percent cured to prevent any deflection in the columns,” Wagner explained.
While the battered columns have been a signature feature of the building's skeleton, it is the combined effort of all the elements that give the structure its strength. The structure of the building is basically a cage suspended 28 feet above grade on columns that act as stilts.
“It's like a cage that's held up on the concrete superstructure legs,” described Vincent Bandy, architect. “Most of the structure hangs vertically from above. We worked very closely with the structural engineer, Magnusson Klemencic Associates, on the design. We wanted to have a condition where you can see right through to the park, with as little support structure on the ground as possible. The northwest corner is completely cantilevered. It hangs from what will act like a tripod.”
W&W Steel fabricated the steel trusses and temporary shoring, which was erected by Bosworth Steel Erectors.
“The box has to be rigid before we release it onto the columns,” Wagner explained. “The steel belt trusses wrap the columns like a belt to keep them from splaying out under the load. Interior trusses between levels 5 and 7 create the big open space in the middle and carry all the load above. The floors themselves are structural – composite with steel beams. Those all have to be poured to hold everything together. The roof has to be poured and it ties back to the vertical concrete shear wall to create a tension element that prevents the northwest corner from deflecting.”
“Our firm does a lot of large structures like convention centers and stadiums, so we deal with temporary shoring issues a lot,” commented structural engineer Owen M. Kohashi, PE, LEED, senior associate with Magnusson Klemencic Associates of Seattle. “But in terms of the final structure being supported on so few elements, I think this is a first.”
“It was a collaborative process the whole way through, with the architect, the engineer and the contractor to come up with a realistic scheme that would work to support this theater on six columns and a shear wall,” said Kohashi. “We had a lot of different ideas of how to build these columns.
“When we deal with theaters, there are so few areas where you can place structure. Nobody wants to sit behind a column,” Kohashi continued. “In this design, we only had opportunities for support around the perimeter. There was also the desire to make it very open in the bottom 28 feet from grade – to make it very transparent. That brought us down the path of needing exterior columns but not having them in the corners where they would block the view.”
|Rendering of the Dee and Charles Wyly Theatre, designed by REX/OMA, at the Dallas Center for the Performing Arts. Image Courtesy of Luxigon.|
Every other construction site skirting downtown Dallas is marked by at least one tower crane, but not the Wyly Theater. “This building didn't lend itself well to a tower crane because of the fact that we are building it from the top down,” explained Chris Arpaia, superintendent for McCarthy. “We have to 'fish' materials in and out constantly. Mobile cranes allowed us to get in and out of the work area.” McCarthy used two mobile cranes for the project: a 225-ton American and a 200-ton Manitowoc.
Organizing the Work
This method of construction has caused the McCarthy team to create an entirely different timetable as compared to other high rise construction. Crews cannot perform very much construction until the structure is completed and the temporary props removed. McCarthy started the project in November 2006, excavating three levels below grade for the foundation structure.
The mechanical room is in the lowest level. The main entrance and lobby will actually be below grade as well.
“From street level, the plaza will drop 20 feet on a sloped angle down to the lobby level,” described structural engineer Owen M. Kohashi, PE, LEED, project structural engineer with Magnusson Klemencic Associates of Seattle. “The stage will be at grade.”
McCarthy started work on the structure above grade in the summer of 2007 and completed that structure to remove the temporary shoring in July 2008.
Jacking Up a Building
In early July 2008, the concrete superstructure of the Wyly Theater was deemed 100 percent fully cured – time for the temporary shoring to be removed. It was the day when everyone would learn if the members of the design team were dreamers or geniuses.
Bosworth Steel Erectors, who had installed the temporary columns ranging in size from 28 feet tall to 100 feet tall, was now removing them.
The Bosworth crew led by Sammy Rojas used two 400-ton hydraulic ram jacks to lift each side of the building in succession to remove the steel beams serving as temporary shoring. The temporary steel support was unbolted and removed with a crane.
“It took us five hours to jack up the building,” said Rojas. “We used one jack in each corner. First we removed the mid-wall temporary columns. Then we used about 6,000 psi to lift the column in the northwest corner half an inch – just enough to release the shim from below it.”
The northwest corner, which has no structural column near it, bears the greatest kip load – about 500,000 pounds, according to Arpaia. The jacking order proceeded in the four corners in descending order of kip load capacity – first the northwest corner, then the southeast corner with its 140-kip load, followed by the southwest corner with a 128-kip load, ending with the northeast corner with only an 80-kip load.
The big concern was how much the building would deflect, or settle, once the temporary shoring was removed.
“They told us that we should expect a 7/16-inch deflection when we took out the first column and we got exactly 7/16-inch,” Arpaia exclaimed. “It couldn't have gone any smoother.”
The seating towers, manufactured by SECOA, with their hoists, manufactured by Vortek, a division of Daktronics, will be 3 stories tall. These movable seating tower sections can be moved forward, backward, and sideways to form many different seating configurations. The seating towers can also be lifted to be stored in the upper stories of the structure.
Floor-level seating can also be moved as needed. The orchestra pit lift, manufactured by Serapid and installed by SECOA, will double as a service elevator to move floor seating into and out of underground “wagon storage.” While most performance halls have only one lift of this sort, the Wyly will have nine lifts to configure floor-level seating into various angles to suit particular performances.
The exterior glass surrounding the ground level theater will have a transmission coefficient of 52 to provide an acoustic barrier from the outside. Above the glass, aluminum pipe of six different diameters will be installed in a pattern to create the illusion of hanging draperies. The aluminum exterior pipe extrusions are being fabricated by Tisi Metals in Argentina.