The giant Beijing Olympic Games cauldron came as the last of many surprises at Friday's opening ceremony, as little was known of it before the final moment.

It was actually a 32-meter steel structure in the shape of a torch, imprinted with patterns of auspicious clouds and wrapped in a red spiral strip that was made to appear like an extension of the "scroll" on which the cauldron lighter was "space-walking".

The builder, Beijing's Shougang Group, had worked for seven months in secret to turn a blueprint into reality for the audience of millions -- building it, hoisting it onto the top of the facility and hiding it there.

Artistic creation vs engineering design

On the blueprint provided by the ceremony organizers, there were just a few specifications: the outline of the cauldron, its rough size, its planned location at the National Stadium, or the Bird's Nest, and the maximum load allowed.

To get the perfect shape expected by artists, engineers said they had to build the cauldron with as many components as possible.

"Steel products used for the cauldron were mostly pieces of handwork, not from mass production lines," said Wang Wenli, Party Secretary of the Shougang Group, China's leading steel maker.

The skeleton was made up of more than 2,000 unique steel pipes ranging in size from 7 cm to 39 cm.

"Cutting out conjunctions that link different pipes was the most difficult part of building the skeleton," said Li Tingxiang, the project manager.

Even the digital cutters failed to produce such conjunctions that could connect pipes of so many different sizes. "In the end, we had to write specific computer programs for the cutters to do the job."

The exterior of the cauldron was composed of 1,026 different 1-mm steel plates, which were heavily perforated to reduce wind resistance.

Engineers did numerous experiments at a site in the capital's eastern suburbs before they managed to build the huge torch, Wand said.

A site was set up for experimenting and construction shortly after the company got the assignment in December last year. It also erected a top-covered rectangular shield to keep it from exposure.

The total cost of the giant cauldron was about 10 million yuan (1.45 million U.S. dollars), Wang said.

In position atop Bird's Nest

How could a 10-story, 45-ton structure get to the top of the Bird's Nest? This was no theoretical question; it was a real challenge builders had to overcome.

Engineers were asked to place the cauldron at a precise location on the northeast top of the stadium, with only a 2-mm margin for error. More than that distance "would have made it impossible for the latches on one side of the cauldron to slot into place," Wang said. The latches were designed to achieve a seamless link with the "scroll".

Making the task tougher was the fact that the stadium itself, built of steel, tends to swell or contract daily with changing temperatures. The height difference could reach 70 cm between the extremes of summer heat and winter cold, according to Shougang engineers.

On the day when the cauldron was lifted onto the roof of the Bird's Nest in May, an 800-ton crane was summoned to the task. The vehicle was the only one with a working arm of more than 570 meters and load-bearing capacity of more than 500 tons.

Workers had to stand on steel beams and yank at ropes against the wind to help lift the colossus smoothly.

The workers held their breath, Li said. "Any collision with the beams would have caused irreparable damage to both."

Stealth before debut

The secrecy of the cauldron became a top priority after it was positioned on top of the Bird's Nest.

A 30-meter upturned-U-shaped air-cushioned facility was set up to house the big torch. The cauldron, which stirred much guesswork before the ceremony, had actually been lying flat on top of the opening stadium for more than two months.

Engineers also designed a rail and a small cart to carry the cauldron, so that the monster could move smoothly above the rugged beam surface from the previous location to the edge of the venue opening.

Hydraulic equipment was used to make it stand up for the flame-lighting, including a hydraulic jack to push it up and another device to hold the bottom.

The whole facility, plus the cauldron, weighed about 405 tons.

The cauldron's final journey, horizontally and up, was designed to start at the touch of a button. Automatic controls were used to minimize accidents.

"We pressed the button at 10:08 p.m. on August 8, when thousands of audiences were attentively watching the parade of athletes, and the cauldron was in place at 10:24 without being noticed," said Su Baozhen, deputy general manager of Shougang.

The torch-shaped cauldron will be used during the Paralympics and might become an item at exhibitions or be recycled afterwards.

(Xinhua News Agency August 13, 2008)