Architects have long turned to the past for inspiration. In this age of glass and steel, however, they're more likely to be looking for aesthetic influence than technical know-how.
But an ancient Chinese construction technique called dougong is a notable exception.
Consisting of a series of interlocking brackets, this building innovation may be more than 2,500 years old. From Beijing's Forbidden City to Sichuan province's Bao'en Temple, it has helped many of China's oldest buildings withstand earthquakes and natural disasters.
And now some of Asia's architects are looking to revive the ancient technique.
Built to last
Many structures built during the Tang and Song dynasties featured "curtain walls" which were, by definition, non-load-bearing. As a result, the unsupported wooden beams that shouldered the weight were prone to cracking and splitting.
Designers needed a technique which would more evenly distribute the burden across their structures. Their solution was dougong.
Translating as "cap (and) block," dougong is a system of wooden brackets that can support the overhanging roofs commonly found in Chinese architecture. The underlying physics are simple: The interlocking brackets transfer weight to vertical columns, lessening the strain on the horizontal beams. Nails or fasteners are not required.
This support system meant that even buildings made from latticework and mud could bear the weight of a heavy temple roof. It also meant that wooden frames became much more flexible while still maintaining their structural integrity -- even in structures of substantial height.
As well as giving the illusion that buildings are "floating" in their frames, this flexibility offers protection against the forces of nature.
Yingxian County Wooden Pagoda in Suzhou, China. Credit: Gisling/Wikimedia
The famous Wooden Pagoda in Shanxi province's Yingxian County is one of countless buildings believed to have benefited from this architectural innovation. Built in 1056, the pagoda straddles the Datong Batin's seismic belt. Yet it has withstood countless earthquakes, even when newer nearby buildings have collapsed.
Historian Klaus Zwerger traces the origins of dougong in his book "Wood and Wood Joints: Building Traditions of Europe, Japan, and China."
"The Chinese building system is based on ratios and proportions," he wrote. "It draws on thousands of years of observations, on which dimensional proportions were structurally suitable and practical, coupled with a growing understanding of which proportions were aesthetically pleasing."
Over time, dougong has become as much about decoration as engineering, according to Nancy Steinhardt, professor of East Asian art at the University of Pennsylvania.
"Decorative rather than functional components first appear in the 13th to 14th centuries," she said in an email interview. "As bracket sets became decorative, they also became smaller in comparison to the height of pillars which interlock with them.
"As one of the most recognizable symbols of Chinese architecture, the use of dougong always references not just Chinese architecture, but China (itself)."
Between tradition and modernity
Engineering has come a long way since dougong was last in fashion. But modern-day designers are now adopting the technique to produce stunning and sturdy works of architecture.
Among them is celebrated Japanese architect Kengo Kuma, who used dougong-inspired methods for two of his recent buildings: Yusuhara Wooden Bridge Museum and Café Kureon, a 2,120-square-foot restaurant in Toyama prefecture.
The China Art Museum in Shanghai -- which was built as the China Pavilion for the 2010 World Expo -- is another modern example. The $220 million-museum's top-heavy design uses dougong-style brackets to support its ever-widening -- and seemingly implausible -- upper reaches.
As in ancient times, the appeal is both structural and aesthetic, according to director and lead architect at Woods Bagot, Jean Weng. Her firm recently drew up concept designs for a 590-foot-high Beijing building called Dougong Tower, an angular design made from interlocking, stories-high blocks.
"We appreciate the history and culture in our projects around the globe, (and) in China we always focus on functionality first," Weng said in a phone interview.
"Beijing is a very historic city, and dougong holds up the Forbidden City. Aesthetics (plays a role) as well, because the shadowing and interlocking (of the brackets) translates well into the building form."
For architect Terrence Curry, the appeal of using ancient methods is about finding something that can "speak to craftsmanship and speak to traditional Chinese identity." His 2015 structure Dougong Cube, which now forms part of the School of Architecture at Beijing's Tsinghua University, was constructed using traditional-style brackets and more than 2,000 laminated boards.
Dougong Cube, Beijing, China by Terrence Curry, Wu Chaoyun, He Shen and Cheng Kun. Credit: photo by Eric Powell
"We had to put screws into the joints," he said in a phone interview. "Normally, we wouldn't do that, but we were (using plywood, which is) different from solid wood. It doesn't expand and contract the way that wood does.
"It has the fundamental structures of dougong, but we (just) aren't using it in the way that it was intended to be used. We're really pulling it out -- emphasizing the beauty and complexity of it, and the intricate way it distributes weight in a very complex way.
"The shape and function of dougong is directly related to the properties of wood, and the extraordinary ability of the craftsmen who made these great buildings. In this way, there is little need for 'decoration' because the structure and the proportion of the building give it its distinctive look."