Executing Calatrava's vision
Since late last year, Milwaukee — a city more renowned for beer and brats than for culture — has been basking in the worldwide attention it has received from a 140,000-sq.-ft. addition to its art museum. The stunning design, by Spanish architect Santiago Calatrava, is highlighted by two slanting masts and a finned sunscreen, or brise soleil, which in its raised position resembles a bird in flight.
This feature, which can be seen for blocks along a principal downtown street, gives the museum a visibility it previously lacked. Civic boosters hope it will become for Milwaukee as notable a symbol as the Gateway Arch is for St. Louis.
Calatrava's brilliance as a designer — he is an engineer and a sculptor as well as an architect — has been widely recognized. Less known is how a Milwaukee-area Building Team executed Calatrava's design, translating a brilliant concept into a physical reality.
Enter David Kahler, principal in charge with Milwaukee-based Kahler Slater Architects (KSA), the project's architect of record. Kahler, who relinquished his role as the firm's president last year to start a consulting company, designed the museum's 1975 addition. His firm subsequently prepared a master plan for the museum.
As it sought an architect for its new addition, the museum wanted "a rising star who had not peaked yet" and whose design would put the museum on the map both locally and throughout the world, according to Kahler. The museum reviewed 73 proposals before selecting Calatrava. The project's construction manager was C.G. Schmidt of Milwaukee.
After Calatrava's office had prepared schematic designs, KSA began developing construction documents. Time did not allow for the normal design development phase, Kahler says. "We just took a great leap from schematic design into construction documents."
The designers in Milwaukee worked from drawings provided by Calatrava's office, as well as his sketches. "He made evocative, heavy-penciled sketches with watercolors to illustrate the spirit of the situation he wanted," Kahler says. "We had to read between the lines of what these said and what some of the DD documents meant, basically consolidating that material and translating it into construction documents."
Because the extensive interaction between the architects' offices was handled electronically, it wasn't difficult to accomplish. "By the next day, we'd have something to work with," Kahler says. This process absorbed about 25% of the computer capacity of Kahler's 130-person office.
Still, Kahler notes, none of the project's details came off the shelf. Calatrava's design vocabulary features compound curves and more organic features than most architects are accustomed to. "As a result, we had to produce more drawings and cross sections for the benefit of the constructors," he says.
KSA designers detailed elements that were indicated by the schematic drawings, with the aim of creating well-engineered details. If the owner decided such a detail it would be too expensive, Calatrava would try another approach. A lot of investigative detailing and design work was performed. "Sometimes we might examine four or five options in order to figure out which one would work," Kahler says.
Twists and turns
Not surprisingly, a major issue for the museum addition's designers and contractors was the constantly curving nature of the structure. "It was difficult to lay out the building and figure out how things meet and work together," says Jerry Kaminski, project manager for C.G. Schmidt. "It was hard to picture in your mind because of the way things twist and turn, even though there's a good degree of symmetry."
Gracefully curved arches are a recurring feature of the art.
To keep the construction on track, Schmidt's CAD engineer at the site deciphered architectural drawings in 1-ft. intervals. "This allowed us to determine, for example, that in a particular plane, the architecture was turning in this direction," Kaminski says. "Then we could create a gusset that would be the proper shape at that point."
Dick Poklar concurs about the project's complexity. He was senior project manager with Super Sky International, which provided all the exterior enclosure except for the roof, consisting of 41,000 sq. ft. of glass and metal panels.
"I think everybody knew up front that if things weren't laid out properly from the foundation all the way up, it would turn into a nightmare," he says. The floors, he notes, are "about the only thing on the whole project that is straight."
The exterior envelope incorporates small skylights at its edges. After continuing down the side of the building, the glazing makes a 90-degree turn and continues downward to form a continuous clerestory extending the full length of the garage.
Glass fabricated with a 45-degree pitch is located in the "prow" of the reception area that extends toward Lake Michigan. Its slope is the reverse of a typical skylight. This glass was obtained from a Spanish supplier because U.S. firms were either unable to fabricate it or could not meet the construction schedule.
Making the impossible possible
Kahler says the most challenging aspect of the project for him "was learning to adjust to the concept of making the impossible possible. If it had been anybody else that did not have Calatrava's engineering background, I would have questioned it and probably say it couldn't be done.
"I trusted Calatrava's ability to do these unusual things," he adds. "I was convinced that since he was proposing some of these things, they were buildable — and they were."
A case in point was the complicated manner in which structural loads were transferred downward from different directions. A ring beam that varies in depth from 8 in. to 20 ft. is central to this process. The mast-supported brise soleil, a bridge that spans a roadway from a parking garage, and the addition's entrance pavilion comprise a highly integrated structure, even though they may appear to be separate elements.
"Calatrava was always striving to make the concrete supports for the ring beam thinner and more dramatic. He would push that particular element as far as he could structurally, knowing that it would work. He understood how far you could push the concrete — always beyond what most engineers would think was possible."
View from Lake Michigan shows movable sunshade (brise soleil) in its closed position. The shading device will close automatically if sensors detect a wind speed greater than 23 m.p.h.
Kahler says the 48-degree angle of the building's two masts was "about as far as you could push the glass. This angle creates more energy in terms of how it looks, and catches peoples' imagination."
Another challenge for Kahler was to learn Calatrava's design language. "Whatever you do basically reinforces what he is trying to do," says Kahler, who comes from a Bauhaus/Mies van der Rohe/Louis Kahn/International background. "I had to make an adjustment to accommodate and work with him. Once I learned his language, I could anticipate pretty well what he needed. But even then there'd be surprises in certain areas."
John Kissinger, principal-in-charge with Milwaukee-based structural engineer Graef, Anhalt Schloemer & Associates, says Calatrava's engineers performed "broad-brush calculations." The architect/structural engineer relationship "was not dissimilar to how we work with most architects, except that up front he was more involved in things like deciding things like bay spacing and approximate sizes of structural elements."
Kissinger notes that much of Calatrava's design concept reflects his structural engineering background. Indicative of Calatrava's intense interest in organic structures was his retention of his dog's skeleton after the animal's death.
He likens Calatrava's design to a strikingly new kind of automobile that doesn't use standard sheet metal, screws, or welding equipment. "The construction industry, although not as standardized as industry in general, still has a fair amount of standardization," he notes. "When you throw that to the wind, it makes the process much more difficult."
The museum site is filled-in lakebed, with most of the lower level of the addition below the level of Lake Michigan, so waterproofing and dewatering were of great concern to the Building Team.
Kaminski says C.G. Schmidt is a company known for tackling challenging projects. He says Schmidt won the construction contract in part due to the firm's understanding and appreciation of the quality issues and of what it would take to get the museum built.
Schmidt initially considered the use of a precast concrete structural system, but was unable to find a precaster who would take the job. Schmidt subsequently decided to place concrete with its own employees. Custom forms were necessary because each element of the building is unique, Kaminski notes.
Quality teams composed of individuals drawn from various concrete-related disciplines were used to reach decisions concerning this aspect of the project. Concrete strengths were not extreme — the highest strength mix used was 6,000 psi.
The key issue was how to effectively place the concrete. In many locations, this was hampered by dense steel rebar. This was particularly the case around steel tubes at the base of columns that rise from hinged connections in the parking garage.
To overcome this problem, concrete mix designs were tailored primarily for workability. Pea gravel mixes, which have no large aggregate, were used to enable concrete to be flowed around the reinforcing steel.
Prior to starting the project, some of the design and construction members of the Building Team traveled to Europe to view Calatrava projects. "We wanted understand the level of quality he was expecting," Kahler says. He adds that Calatrava "had more confidence in America's technology than we did. He knew what Americans have been able to accomplish technologically. When all is said and done, most of the components were fabricated either in Wisconsin or at other U.S. locations. Workmanship was as good, if not better, than what we saw in Europe."
A passion for the job
But technical expertise alone would not have been sufficient to execute the project, Kahler emphasizes. "We had to convince ourselves and everyone else who worked on the project that that you had to have a passion to do it properly. If you didn't, you shouldn't be working on it, because it would give you a lot of heartburn, and you'd lose a lot of money. You had to be passionate about doing it right."
Recalling the beginning of this unusual project, Kahler says, "Calatrava didn't know me. I knew his work, but not him. Fortunately, we developed a mutual respect and friendship. It worked very well."