Architectural Masterpiece Challenges the Art of Engineering
Reinforced Concrete Design in Milwaukee Art Museum Addition
Structural elements dominate first impressions of the Quadracci Pavilion addition to the Milwaukee Art Museum. Designed by architect Santiago Calatrava, the building has received international acclaim from the day it opened in late 2001.
The 142,000-square-foot building, with its iconic wing-like sunscreen and sweeping prow and canopy elements, is a remarkable achievement of engineering and architectural vision. The design using reinforced concrete is a study in how Calatrava, in collaboration with other structural engineers and members of the project team, met the challenge of implementing his idea of a showcase project that portrays a sense of motion and change.
Initially proposed in 1994 when the Museum invited the Spanish-born architect, structural engineer, and artist with a reputation for daring and innovation to submit a design. Calatrava's concept, his first U.S. commission, takes inspiration from the site along the Lake Michigan shoreline where the building stands as a dramatic, memorable presence.
The Milwaukee-based engineering firm of GRAEF joined the project in 1996. GRAEF's team, led by John Kissinger, PE, served as structural engineer of record, site/civil engineer, co-landscape architect (with the office of Daniel Kiley), and preliminary environmental engineers.
In 2008, Kissinger presented the Quadracci Pavilion as a case study in a session for a workshop on Reinforced Concrete Design at the University of Wisconsin–Madison examining various aspects of structural design. This article expands on comments from that talk along with additional insights from Lou Stippich of Kahler Slater Architects in Milwaukee architect of record.
Engineering a vision
The approach Kissinger and the GRAEF team took to implement the design and meet every expectation of constructability and presentation begins with effective use of a reinforced concrete structural system.
"The shape of the building lent itself to the use of concrete," Kissinger says. "It was the natural choice for the job and complements the structure's sculptural look." He adds that concrete fits with Calatrava's preference for using a local material with fluid, moldable qualities. He notes that today, their use of concrete would earn the project points for sustainability.
The other primary materials are metal and glass, evident in features like the steel of the movable sunscreen and the glass roof that soars 90 feet above a central hall.
Stippich and his team acted to translate and meet Calatrava's vision, working closely with the owner and the project team. He explains that aesthetics played a big role on the Pavilion project, more than on most projects. "The Museum wanted this to be an icon, a piece of art in and of itself."
Floating the foundation
Creating a structure that commands visual prominence on the City of Milwaukee skyline was at the heart of many design decisions. But one of the first challenges was designing the foundation. The building site was an abandoned landfill along the lakeshore. Beneath the fill and below lake level, however, Kissinger says the site had competent bearing strata.
The team designed a mat foundation to spread the load and allow installation of a more-robust waterproofing system—important in a facility used to store and exhibit valuable artwork. He describes the mat as a thick slab of concrete "built like a raft." The foundation takes advantage of the buoyancy of such a system and, because there are no pilings, it avoids excess edges and turns where moisture can penetrate.
Models meet challenges
The project team relied on three-dimensional mock-ups—some full scale—to identify solutions for translating the concept into reality. Kissinger says this process proved invaluable in designing the exposed concrete arches, some with arresting compound curves that define the interior spaces.
The unique trapezoidal shapes of the arched support structure create a focal point as they sweep from slender base to deep sculpted beam in the upper reaches. The arches vary in subtle ways from the main hall to the jutting south canopy. Multiple arches come together here in a complex juxtaposition of angles, curves, and connections. Using a physical model helped the construction team execute the formwork and position the arches to meet aesthetic requirements.
"Among the several valuable revelations I took away from this experience is the result we got from using these mock-ups," Kissinger recounts. He recalls that, at the time, Calatrava did not trust computer models to answer the difficult questions. "Even with advances in the technology, I think physical models often are the best way to resolve the tough issues."
Kissinger says the models ultimately helped all the trades understand how this complex area affected their work. Stippich agrees, noting that they gave the contractors an opportunity to study how to achieve the proper smoothness and shape of the concrete as prototypes for the finished concrete work.
Some of the physical models also doubled as valuable tools for fund-raising, an active effort throughout construction of a facility entirely funded with private dollars.
Concrete finishes: achieving distinctive look
The luminous appearance of the Pavilion's reinforced concrete design is one of its most distinctive features. The exterior expanses are strikingly white and the inside arches appear flawless and unblemished.
Stippich describes researching how to achieve the look of a uniform white (or off-white) concrete on the exterior—Calatrava's preference. He explained to the lead architect that the appearance of concrete placed in different temperatures and under different weather conditions is likely to vary, especially the color. Because the concrete work extended over at least a full year, the material would be cast or placed in Wisconsin's mix of high heat and humidity, extremely cold and dry conditions, and everything in between. "Calatrava understood and agreed this was a concern, so we investigated other solutions."
The one they found was to finish the concrete with a coating that allowed a variety of white options. Stippich says it gave the construction team an opportunity to match the finished concrete to the white color in other design elements. They assured proper bonding by careful preparation of surfaces with light sandblasting according to the supplier's instructions. Doing so also helped the project negotiate a 20-year warranty on the coating and achieve the goal of controlling maintenance costs.
Paint is the finish of choice on exposed concrete surfaces inside the welcome hall and exhibit spaces. The goal was to create the look of clean, distinct lines and a smooth feel to the surfaces as far as people can reach. The team used drywall compound rather than a cement wash to fill the minor "bug holes" in the concrete before painting it to produce the desired tactile and visual appearance. Kissinger comments that this is less of an issue today thanks to advances in concrete mix technology. But in the late 1990s, it took some testing to find an effective approach.
"It was important to us and others on the team," he says. "We all felt the building demanded attention to detail, and we wanted to get it right."
Ensuring the smooth finish of the concrete members started with the forms. The contractor had them made on site from solid pieces of wood planking, many of them displaying furniture-quality craftsmanship. Forms were shaped to the exact curves specified for each arch and then coated inside with a fiberglass material.
The construction team then developed a concrete mix using a smaller-than-normal aggregate that allowed the material to flow evenly into the forms and around heavy steel reinforcement.
Finally, they removed air bubbles by applying external vibration to the forms. The result gives the cured concrete surfaces a distinctive elegance that belies the raw materials.
Good communication promotes collaboration
Charged with communicating the architect's vision, Stippich concentrated on understanding design intent and documenting key issues in the early stages. His advance work helped the project team establish shared goals and set a standard of collaboration—important on a building everyone from the donors to the sub-contractors expected to become a landmark. "We thought through every detail in accord with the design concept requirements, taking time as we went to consider what's right and what's not," Stippich says.
An example of taking the time to get it right was coordinating placement of mechanical and other elements in the interstitial space between floors. The main level has no ceiling to hide pipes and ducts, making it a challenge to accommodate the size of utility chases necessary for the Museum's complex mechanical requirements related to climate control, back-up systems, and other demands. Structural and mechanical engineers worked together to determine the size and position of openings in the concrete beams. Ultimately, the team succeeded in placing a series of oval openings to meet mechanical needs without compromising structural strength or visual impact.
Stippich and Kissinger both describe the Museum addition as a special project where they routinely researched such major decisions and made modifications cooperatively. Stippich stayed in regular touch with Calatrava and the owners to review solutions, and the project team moved quickly to find and apply them. Thanks in part to this approach, the project stayed on track and opened to considerable fanfare in October 2001.
Concepts advance innovation in reinforced concrete design
As with other structural systems, advances in reinforced concrete design depend on understanding materials and methods. The Quadracci Pavilion demonstrates how the project team proved the method's constructability by exploring and adapting some exceptional approaches to the complexity of unusual and changing concrete shapes.
Kissinger says he and others on the project gained insights throughout the design and construction process. "Several concepts I embraced and continue to apply came from working with Calatrava, in particular the idea of leaning elements that create the kind of counterbalance and symmetry we find in nature." He concludes that Milwaukee's modern masterpiece is a good example of aesthetics supported by the material and method, a unique canvas for innovation in structural design.
Structural engineers can benefit from similar case studies and the latest technical information provided by many top experts by attending workshops offered by the Department of Engineering Professional Development (EPD) at the University of Wisconsin–Madison.
For details on future workshops, contact EPD program directors. Learn more by visiting our Courses. Or call 800-462-0876.
Written by Mary Maher
This material is based upon work supported by the University of Wisconsin–Madison Department of Engineering Professional Development. It is for general information and distribution and not intended to provide specific solutions or advice for specific circumstances, which should be sought from appropriate professionals.