Some see a frozen tear clinging to the “cheek” of the new Salvador Dalí Museum in St. Petersburg, Florida. Others see a melting crystal. Depending on the viewer’s vantage point, still others say they are reminded of a misshapen potato, a nose, an amoeba and a dolphin in a nosedive. The builders of the glazed atrium structure that drapes over the side of the boxy building simply call it the “enigma.” After all, the builders had to solve a mystery of how to shape, engineer and hang a transparent and organic structure—75.5 ft at its tallest, 105 ft at its widest and 27.5 ft at its deepest—and still ensure the delicate-looking structure can withstand hurricane-force winds and windborne debris.

“No one thought this was achievable,” says Mark House, managing director of the Tampa office of The Beck Group, the $29.8-million job’s construction manager at risk.

But even with the complex atrium structure, the Dalí museum is poised to open Jan. 11—on time and $700,000 under budget. “[Based] on cost per sq ft, it is one of the least expensive museums built in the last 10 years,” says House, who notes that Beck and the museum split the savings.

The 68,000-sq-ft museum consists of a cast-in-place, 58-ft-tall reinforced-concrete box with one-way slabs and beams. Mostly for economy’s sake, the three-story building’s 18-in.-thick perimeter walls are architecturally exposed on the outside, with no stucco or painted surfaces. All the museum’s art, mechanical equipment and computers are housed on the second and third floors to keep them well above the flood line. On the face of it, the building had to be a fortress to resist 165-mph hurricane winds and “the occasional flying yacht during a storm,” says Yann Weymouth, director of design in the Tampa office of architect HOK Florida.

But the architect wanted something provocative inside the mostly rectilinear box as a way to invite the visitor upstairs to the third-floor galleries. A grand spiral stair, crowned by a rooftop skylight, did the trick. The skylight then morphed into the enigma to contrast with the conventional shape of the building, says Weymouth.

Weymouth dubbed the structure the enigma because of its mysterious shape, which wraps around two sides of the building and ends on the roof over the grand spiral. Enigma is also the name of a 1929 painting by Dalí, who was known for surreal artworks with jarring juxtapositions, much like the ordinary box and the free-form enigma and its smaller-entrance sidekick, dubbed the igloo.

The faceted, glazed form, which curves without curves, is “very Buckminster-Fuller-like,” says Weymouth, referring to the inventor of the similarly triangulated Geodesic dome. But “a dome would have been corny,” especially against the Cartesian, Euclidean box, says the architect. The project team might accuse the enigma of being surreal, but never corny. For though they all look alike, no two of the system’s 1,062 triangular glass facets or the 3,000 steel pieces that frame them are dimensionally similar.

It’s as if all they were working on a jigsaw puzzle in which all the pieces were the exact same color, says Ian Collins, CEO of Novum Structures, Menomonee Falls, Wis., which engineered, manufactured and installed the 13,025-sq-ft glazing system under a $2.6-million contract. The entire enterprise, including the geometry and structural and wind analyses, was made possible by computer power. “Bucky couldn’t have done this,” says Weymouth, who selected Novum to supply the system.

Straight, Flat Free Forms

The atrium is the first major installation in the U.S. of Novum’s free-form system. For five years, the firm has been developing its method to modularize free forms and create any shaped surface from straight lines and flat surfaces. Structural analysis to fabricate the pieces has to be automated, including machining the nodes using computer-numerically controlled (CNC) cutting equipment, says Collins. “Otherwise it is a nightmare,” he adds.

HOK used a bevy of digital design tools, including 3D building information modeling, as well as physical models to develop the surface geometry. Then, Novum took HOK’s BIM into its proprietary engineering and fabrication software. The final tessellation, or collection of plane figures that fill a plane with no overlaps or gaps, was determined by Novum’s structural algorithms in order to optimize the glass size for transparency and views. It also helped to minimize the weight of the steel frame. “That would save money, save on joints and save on labor,” says Weymouth.

Novum’s strategy during the two-year preconstruction phase was to normalize the atrium’s grid and optimize the surface geometry while maintaining a shape acceptable to HOK, says Collins. The best-case scenario for optimal cost and fabrication of regular triangular geometries is to use same-size glass shapes and beam lengths, says Collins. For a free-form shape, the goal is to make the glass panels and beams as close in size as possible.

Another goal is to minimize angles under 40 degrees between adjacent components. The rationale is that, as the angle gets smaller, the connection has to get bigger because the members start to collide. Collins says the 40-degree rule was only violated in a dozen places out of about 3,000 connections. The radial system contains triangular glass panes, 6 to 8 ft on a side, edge-clamped onto a triangulated structural steel framework consisting of 3 x 8-in. rectangular tubes bolted into a double, circular node. Each node receives six tubes. All the members are straight.

Once the kit of parts is fabricated, the installation is just an inventory control problem because of the thousands of different parts, says Collins. Every piece had a bar code. For House, Weymouth’s selection of Novum was an early concern. “There was no other subcontractor or manufacturer that had anything like it,” says House. “If something went wrong, there was no plan B,” he adds.

House was also concerned about water leaks. But the structure, which has been enclosed for six months, hasn’t leaked yet, he says.

Another concern during the project was schedule, especially because myriad, one-of-a-kind pieces of the puzzle were coming from several faraway places, including China, Germany and Wisconsin. When a piece of glass broke, a replacement had to be ordered from China, says House. There were no duplicates of anything on site.

About 10 pieces of glass broke during installation. All of House’s other concerns dissolved during construction. Novum met the schedule, says House. The budget, which Novum offered early in schematic design, “didn’t go up at all,” despite some changes in design, he adds.

The installation, which started last January and was done in September, progressed at a snail’s pace for the first two weeks, as workers oriented themselves.

The key was to set the first pieces correctly, says Collins. Production, which started at 20 tubes per day or less, sped up to 80 tubes per day.

Work proceeded from the ground up. The system is bolted together and then welded to the building’s concrete frame at about 30 nodes. At the base, outbound of the concrete box, the atrium sits on a concrete curb via embeds.

The frame, which has rigid connections, had to be propped up until workers adjusted the connections to the concrete. Unlike a lot of bolted structures, workers prestressed the bolts as they installed the frame, rather than at the end of the installation, says Collins.

Water Worries

The concrete perimeter walls are 18 in. thick, instead of the 1 ft needed to resist 165-mph winds, because “we were worried about water migration” through the walls, says Scott D. Martin, a senior associate in the Tampa office of the project’s structural engineer, Walter P. Moore & Associates Inc. (WPM). To further guard against leaks, the engineer specified self-consolidating concrete, which contains a crystalline admixture. During casting, when the crystals get wet, they expand and fill any voids in the concrete.

The extra thickness also helps resist the high forces imposed by the Novum system. Novum and WPM collaborated on how the forces, including wind loads, would tie back into the structure. “They would model their system and send us spreadsheets with tables and tables of forces, which we would analyze,” says Martin.

During design, the engineer noticed that the shrinking and expanding of the Novum system in response to temperature variations would cause uplift on the building’s shallow foundations. The engineer considered putting in tension piles to resist the collective uplift, but that would have meant a more costly foundation system. Instead, Novum modified its connections, allowing more play by a fraction of an inch at each node to allow for thermal expansion and contraction. “If you try to resist the force [at the foundation], it’s a huge force but if you release the force locally, instead of allowing the entire system to expand and contract, there is no force to resist at the foundations,” says Martin.

Thanks to the Novum structure, the engineer had to deal with yet another force. Novum said its system could not resist the pressure from 165-mph winds, so WPM had to come up with a way to protect the contents of the art galleries and the art vault in case of a breach in the atrium. The solution: 1-ft-thick interior masonry walls designed as perimeter walls, with heavy reinforcement and waterproofing.

The remainder of the structure is conventional, says the engineer, with the exception of architect Weymouth’s reinforced-concrete spiral stairway—a single helix that rises 65 ft from the foundation and is supported at the foundation and the third floor slab. The upper 35 ft, which tapers almost to a point, is a vertical cantilever. “It’s a giant concrete spring,” says Martin.

The stairway consists of a spiral wall, with a 12 ft, 4 in. inside dia and a 14 ft, 8 in. outside dia. Stair treads and risers cantilever horizontally from the wall, 3 ft, 8 in.

The springy stair presented serviceability issues in terms of floor vibrations, and construction sequencing challenges. “It had to be built so its own weight didn’t cause it to compress,” says Martin. The concrete subcontractor, Reinforced Structures Inc., Clearwater, Fla., had to survey and recalculate the rise and run after every pour of the corkscrew, making adjustments to the forms for the next lift so that everything was in position.

The building team completed the museum in 22 months. Everyone is satisfied with the result in general and the enigma in particular. HOK’s Weymouth calls the Novum system a visual diagram of the way the structure performs, because the triangles get tighter in places of the greatest stress. “But the diagram is also pretty because the triangles spiral in unexpected ways,” he says. “In the end, some of the beauty is that you are just looking at physics,” says Weymouth. “It is like being inside of a formula, inside the structural algorithm that is optimizing the structure.”