Welding of steel structure was completed at the main stadium of the Beijing Olympic Games on Thursday.

Workers finish welding of steel structure of the Bird's Nest. [BOCOG]

Over 100 skilled welders started their work last Wednesday, using a total of 2 000kg of welding rod. They overcame two technical difficulties. One is the rigorous temperature requirement: it should be 19 plus or minus 4 degrees Celsius. The other is that the welding joints amount to as many as 128 with a combined seam length of some 600 meters.

The National Stadium is dubbed "the Bird's Nest" because of the shape of its structure. The structural elements mutually support each other and converge into a grid-like formation - almost like a bird's nest with its interwoven twigs. The whole steel structure weighs 42,000 tons and when completed, it is believed to be the world's largest enclosed space.

The stadium, 333 meters long by 284 meters wide and 69 meters tall, will seat 91,000 spectators during the Olympics and will be used for the opening and closing ceremonies, track and field events and football finals. Its construction started in December 2003 and it is expected to be completed at the end o 2007.