BBC documentary reveals secrets of Forbidden City(2)

A dougong (highlighted in white). [Photo/Screen capture of Secrets of China's Forbidden City]

Modern science suggests that ancient Chinese people used ice.

Each winter, Beijing freezes. Scientists featured in the documentary speculate that workers put the large marble onto the frozen rivers and added a little bit of water as a lubricant to reduce friction. Calculations suggest that only 180 men were necessary to move a rock weighing more than 300 tons.

Earthquakes

Beijing sits in a very active seismic hub.

In its 600 years, the Forbidden City has withstood over 200 devastating quakes, including the deadliest earthquake of the 20th century in Tangshan, which centered around 153 km east of the capital. The Tangshan earthquake in 1976, 7.8 in magnitude, obliterated the city and killed nearly one quarter of a million people in just 15 seconds.

In a stark contrast, the Forbidden City suffered minimal damages.

Experts believe the secrets lie in dougong, an architectural element commonly found in traditional East Asian architecture.

A dougong is a complex bracket that supports the huge roof. At first glance, it looks like an elaborate decorative feature. But the unique design is the structural key to every Forbidden City building.

In traditional Chinese architecture, there are no nails or glue, nothing holding it together other than blocks of craftily designed pieces of wood locking against one another, and sheer ingenuity.

A resident seismologist of the Forbidden City, surnamed Zhou, created a shake table calibrated to the size and weight of a 1:5 scale model of a typical building in the palace to replicate the energy of quakes in increasing magnitude and simulate how much quake forces the architectures can take.

Under a simulated earthquake of magnitude 5, walls around the model pavilion began to crumble but the pavilion stood upright in its complete form. At magnitude 9.5, an energy equivalent to 200 tons of the explosive TNT, the supported columns started to move but did not crack. At 10.1, the highest level tested, the pavilion still stood high.

The secret can be summarized in one word -- flexibility.

The dougong acts like a shock absorber in a car and there's both friction and rotation that absorbs the energy from the earthquake.

Something as simple as a craftily cut piece of wood, that was designed more than 2,000 years ago, reached their zenith in the Forbidden City and protected the impregnable fortress from natural disasters for centuries.

The vision of one man may have wanted to steer China into a whole new direction, but it was the genius of the Chinese people that made it possible.

Secrets of China's Forbidden City is a co-production between China Intercontinental Communication Center and BBC.