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Civil Engineering Magazine THE MAGAZINE OF THE AMERICAN SOCIETY OF CIVIL ENGINEERS

Milan Expo 2015 Highlights Countries’ Plans and Traditions

By Catherine A. Cardno, Ph.D.

Once again, countries around the world gather for a universal exposition-or World Fair-highlighting their cultural traditions and future plans.

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The 4,000 sq m China Pavilion is visually dominated by its steeply undulating roofline inspired by both the soft, rolling hills of a typical Chinese landscape and the sharp inclines of an urban skyline. Courtesy of Studio Link-Arc/© Sergio Grazia

May 19, 2015—Universal Expositions, also known as World's Fairs, are a 164-year-old tradition. Dating back to London's Great Exhibition of 1851, which launched the city's famed Crystal Palace, such fairs were held at the behest of the hosting nations—including the Paris Expo of 1889 that introduced the Eiffel Tower to the world stage. In 1928, the Paris-based Bureau International Des Expositions was formed to aid the planning of worldwide expositions, and to provide guidelines as to their size, scope, and quality. In 2010, the Shanghai Expo was held; this year, the Milan 2015 Expo opened on May 1 with the theme "Feeding the Planet for Life."

Given that the pavilions need to celebrate the theme, remain in heavy use for six months, and then be removed from the site without a trace, it is surprising that only a few countries chose to design structures predominantly in wood. But China, France, and Estonia did just that, and the results are remarkable. 

The design for the China Pavilion was created by Tsinghua University in Beijing and New York City-based Studio Link-Arc, which worked in close collaboration with the New York office of the engineering firm Simpson Gumpertz & Heger (SGH). The pavilion is China's first national pavilion to be located outside of its borders, according to material provided by the architects.

The 4,000 sq m Chinese pavilion is visually dominated by its steeply undulating roofline. Bamboo roof tiles—1,052 in total, presented in 287 different iterations—top the roof. A small, planted field surrounds the pavilion, representing China's agricultural traditions, according to material provided by the architects.

The pavilion "focuses on sustainability and the coexistence of nature and city," said Holger S. Schulze-Ehring, Dipl.-Ing., CEng, SIA, M.ASCE, a vice president of SGH and the lead structural designer for China's pavilion. Schulze-Ehring wrote in response to questions posed by Civil Engineering online. 

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The complex geometry of the China Pavilion roof profile was achieved through the use of glue-laminated wood beams. Thin strips of bamboo create the roof tiles, allowing the center of the pavilion and its “Land of Hope” installation to be dappled with daylight. Courtesy of Studio Link-Arc/© Sergio Grazia

"The China Pavilion is actually based on a very simple idea," added architect Yichen Lu, a principal of New York City-based Studio Link-Arc and an associate professor at Tsinghua University in Beijing. Lu, who wrote in response to questions posed by Civil Engineering online, is the chief architect for the China pavilion. "We created the roof form by combining two separate profiles," he explained. "The first profile, on the north, is a city skyline. The second profile, on the south, is a rolling landscape. We merged these two shapes digitally, and the resulting form became the building."

Sharp-edged, angled timber rafters shape the back of the pavilion's roof, on its northern side, and gentle, soft waves define the structure's southern side, which is its front, according to Schulze-Ehring. "These inherently opposing profiles are merged by longitudinal timber members connecting cityscape and landscape to create a ruled surface in between them," said Schulze-Ehring.  

"SGH selected glue-laminated timber (glulam) for the primary rafters and purlins based on its strength and stiffness, geometric flexibility, and aesthetics," Schulze-Ehring said. This choice made the long spans, cantilevers, varying elevations and complex geometry of the pavilion possible, despite the fact that there are very few columns, according to Schulze-Ehring. "The rafters—spaced at 2 m on center—are each different in overall shape to form the desired roof profile," he said. "By discreetly locating columns where interior walls or slabs were close to the roof structure, SGH accentuated the architect's desire for minimal support and openness at the exhibition spaces." 

The pavilion also contains a series of unique structural features, according to Schulze-Ehring. These include cable trusses that are embedded into the roof geometry, exposed glulam columns, and an interior steel-and-concrete structure that appears to grow from a field of light-emitting diodes.  

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Glue-laminated timber creates uniform lattice girders and pillars to form the French Pavilion, which appears as an upside-down hill and valley. Visitors walk along the plane of the sky, while the ceiling rises and falls above. Courtesy XTU Architects

The interior of the pavilion is illuminated by daylight that filters between the edges of the thin bamboo strips used on the roof tiles and through a layer of waterproofing located between the tiles and the roof's supporting structure. "We wanted to create a roof with shingles that would reference traditional Chinese ceramic roof tiles—however, we needed to reduce the weight on the structure," Lu said. "We liked the idea of bamboo, since it is uniquely tied to Chinese culture and history, and in addition it is very light," he notes. With the light filtering into the pavilion, "it's like being beneath a canopy of trees," Lu noted. 

"Achieving a roof structure that seems to float above the pavilion's [central] 'Land of Hope' [installation] was the main challenge," Schulze-Ehring said. "A timber grid system defined by a one-plane rafter-and-purlin solution forms the roof's major [structure and] … allowed for the desired two-directional long spans while maintaining a lightweight structure," he explained. "The array of parallel but curved continuous rafters intersects with the longitudinal, mostly straight, discontinuous purlin members at regular intervals to create an evolution of the diagrid." 

Schulze-Ehring explained that this design creates "a three-dimensional orthogonal system with partial moment connections in each primary member axis," noting that biaxial partial moment connections are used for many members.

"The complexity of the roof structure translates into a similar complexity for the structure beneath," Lu added. "Bear in mind that we were trying to hide columns and bracing as much as possible. It was like a puzzle—very intricate."

Glulam timber was also the material of choice for the French pavilion, which appears as a hilly valley—albeit upside down, visitors walking along the plane of the sky while the ceiling rises and falls above. Uniform lattice girders and pillars create the pavilion's dips and rises in homage to France's diverse geographical topology, according to material provided by the agency that designed the pavilion, Paris-based XTU.

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The 1,200 m2 Estonia Pavilion was designed to appear as a series of wooden “nestboxes” stacked atop one another to form the main volume of the building. Courtesy Kadarik Tüür Arhitektid

"It was an obvious fact to choose wood as [the] main material—compared with other structuring materials, wood is the most environmental," reads a statement by Anouk Legendre and Nicola Desmaziere, the architects and founders of XTU, which they provided in response to questions posed by Civil Engineering online. "The glue-laminated structure is completely made of French wood: the interior in spruce and the exterior in larch," the architects wrote. 

Estonia's pavilion also centered on wood as an expression of its sustainability, according to material distributed by Kadarik Tüür Arhitektid, an architecture firm based in Tallinn, Estonia, which designed the 1,200 m 2 pavilion. The design called for a series of glulam "nestboxes" that could be stacked atop one another to form the main volume of the building. Unfortunately, site constraints kept the design from being built as specified. Low water volume at the Estonia site prevented the team from installing the necessary sprinkler system for a wood structure, so they used a structural steel system instead. 

Although construction delays and protests marred the opening of this year's celebration, the Milan Expo, which will remain open until the end of October, is expected to draw more than 20 million visitors to its 1.1 million sq m of exhibition area. More than 140 countries are presenting technologies aimed at guaranteeing healthy, safe, and sufficient food sources that do not diminish the environment.

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