Where majesty meets math

Museum's delicate beauty can only be realized with precise engineering

By Jack Bess

Architect Santiago Calatrava describes the museum he envisions, but engineers are making the design a reality with innovations like concrete arches rising from the east side of the galley pictured below. Photos: James W. Brozek; Click on photos for larger image.

To begin with, the wings won't blow away.

That's usually one of the first concerns that John Kissinger addresses when people find out he's working on the Milwaukee Art Museum expansion.

People naturally ask about it because the "wings," the name given to the louvered sunscreen formally known as the brise soleil, has received much of the media attention so far, said Kissinger, a vice president at Graef, Anhalt, Schloemer & Associates Inc., which is providing the structural and civil engineering on the project.

The wings are magical, Kissinger said, for the images they evoke. In the model, they raise and lower, seemingly like a sail, a flower opening its petals or a bird taking flight.

They seem too delicate to last.

Grounded

But Kissinger reminds his questioners that the sunscreen is much sturdier than it looks.
Originally, architect/designer Santiago Calatrava wanted to use aluminum for the brise soleil's fins, but the project team chose carbon fiber -- strands of carbon glued together with epoxy -- in order to reduce the weight of the sunshade, Kissinger said.

Reinforcing steel lines in the the museum's "ring beam." From this angle, looking west across the addition under construction, The Calatrava looks like a ship setting sail on Lake Michigan. Photo: James W. Brozek; Click on photo for full image.

The substance "is widely used in manufacturing but the use of that in buildings is somewhat in its infancy," Kissinger said. Carbon fiber is used in such products as boat masts, auto-body parts, aircraft pieces and packaging. In other words, for uses requiring light weight but great strength.

The brise soleil will have a "wingspan" of 200 feet from one tip to the other, and be composed of 72 fins, ranging from 20 to 102 feet long. The longest fins will weigh close to 1,500 pounds.

The brise soleil will be attached two rotating spines that are connected to the main building spine, Kissinger said. A hydraulic system will move the spines, but there are several backup power systems.

"And if all else fails, we have a little propane engine that can lower the brise soleil," said Jerry Kaminski, project executive with C.G. Schmidt Inc., the construction manager. "Everything has been thought of to make sure those wings can close, no matter what the conditions. We'll never be in a position where the wind is so strong that they can blow off."

Anemometers will measure wind speed and automatically trigger the sunscreen's closing mechanism if the wind goes over 30 miles per hour. That figure was chosen after a meteorological study of the actual wind conditions showed that "the wind doesn't blow over 30 miles per hour all that often and it blows over 40 miles per hour much, much less," Kissinger said.

The mechanism can be reprogrammed to close the sunscreen at lower or higher wind velocities if experience shows that the brise soleil is opening and closing too often.

A bird or a ship?

Another prominent design feature is 90-foot stretch of concrete that soars out toward Lake Michigan from under the building.

That detail is part of the support structure called the "ring beam," one of the terms coined on this project to describe elements that no one has used before, Kaminski said.

To understand the ring beam, you have to envision a football cut in half, Kaminski said. The outer edge of the football would be the beam of concrete, about 300 feet long from tip to tip. That beam has four legs, each arched in toward the center. So these legs support the concrete ring beam, which in turn supports the pavilion of glass, the main entrance and the reception hall, he said.

But the tips of the concrete beam are cantilevered out, 60 feet on one end and 90 feet at the Lake Michigan end. That 90-foot section, from the last support to the lake, "is a long cantilever for concrete where there's no visible support underneath it," Kaminski said.

The floating bridge

Eyebrows are expected to take another jump when spectators gaze upon the cabled pedestrian bridge linking the museum to O'Donnell Park and passing over North Lincoln Memorial Drive. The bridge will be suspended by cables from a 192-foot steel mast that tilts away from the museum.

"People are used to seeing something with a support on one end, a support on the other end and something spanning in between," Kaminski said. "Now they'll see a bridge with a mast that's laid back like that and cables coming off of that and it's going to look confusing to them."

While there is a support on the O'Donnell park side, that won't carry the bridge's weight but rather stabilize it, keep it from moving from side to side, he added.

Someone might expect the mast to be vertical and penetrate through the bridge deck then go into the ground. Instead, the mast, which pedestrians will pass under when they take the bridge, will tilt down and hit a large oval-shaped steel piece called the "hammerhead" (another term coined for the project). The hammerhead spans two heavy steel supports dubbed "boomerangs" (still another project coinage) for their shape, and these boomerangs are tied to the ring beam with high-strength cable.

So while the bridge doesn't have a corresponding mast carrying weight on the bridge's other side, the structure is in balance, Kissinger said.

"It's like if you were fishing and you were catching a large fish," Kissinger said. "You would lean your body back to counter-balance the weight (of the fish). You might put your feet against the side of the boat for support, or you'd just slide away.

"That's kind of how the mast works. What's nice about the mast being at an angle is that it counter-balances the weight of this bridge. The boomerangs are what you would put your feet up against, like the side of the boat."
Working on Calatrava's innovative design "really gives you an appreciation why most people design buildings that are square or rectangular or orthogonal, and use standard materials -- two-by-fours, wide-flange beams, stuff like that," Kissinger said. "When you decide you're just going to make up everything -- make up the shapes, make up the materials, like we did on this project -- it's exciting but it really makes it a lot more difficult to engineer."