Bird's Nest, a tightly woven lattice of steel
2008-07-30

Beijing National Stadium, also known as the bird’s nest is the main track and field stadium for the 29th Olympiad in 2008. Located at the southern part of the Olympic Green in Beijing, the National Stadium occupies an area of 21 hectares which has a floor space of 258,000 square meters. Its seating capacity amounts to 91,000, including 11,000 temporary seats.
Designed by Pritzker-winning architects Jacques Herzog and Pierre de Meuron, the building was commissioned in 2002. Their ambitious design has called for 45,000t of unwrapped steel knitted in an intricate open-weave structure to form the gentle curving basis of the stadium. The final building will house 91,000 spectators, alongside shops, restaurants, cafes, bars and meeting spaces. The main body of the National Stadium is a colossal saddle-shaped elliptic steel structure weighing 42,000 tons. It is 333 meters long from north to south, 294 meters wide from east to west, and 69 meters tall. Because the structural elements in the project are box-typed, many elements intersect spatially among the steel parts. And the complex nature of secondary structures has resulted in the diversity of nodal joints of the main structures, requiring accurate and sophisticated installation and Strength of the steel during the process.

The "nest" is a tightly woven lattice of steel in fact. The roof of the centre is a steel skeleton sheathed in a Teflon-like plastic membrane. Its unusual design was created by twisted steel beams that wrap around the exterior to resemble silver twigs binding a nest together. The welders not only face a huge work volume, but also have to work on both the thin steel sheets and thick steel slabs, on high-strength and cast steel elements, and take downward, vertical or overhead positions while welding. The difficulty is that the welding joints amount to as many as 128 with a combined seam length of some 600 meters. They face temperature changes, steel deformation and intensive labor. They need to work above ground, in winter rain and under windy conditions.
In fact, many different energy sources can be used for welding, including a gas flame, an electric arc, a laser, an electron beam, friction, and ultrasound. While often an industrial process, welding can be done in many different environments, including open air, underwater and in outer space. Regardless of location, however, welding remains dangerous, and precautions must be taken to avoid burns, electric shock, eye damage, poisonous fumes, and overexposure to ultraviolet light.
welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. One of the most common types of arc welding is shielded metal arc welding (SMAW), which is also known as manual metal arc welding (MMA) or stick welding. Electric current is used to strike an arc between the base material and consumable electrode rod, which is made of steel and is covered with a flux that protects the weld area from oxidation and contamination by producing CO2 gas during the welding process. The electrode core itself acts as filler material, making a separate filler unnecessary.
Spot welding is a popular resistance welding method used to join overlapping metal sheets of up to 3 mm thick. Two electrodes are simultaneously used to clamp the metal sheets together and to pass current through the sheets. The advantages of the method include efficient energy use, limited workpiece deformation, high production rates, easy automation, and no required filler materials. Weld strength is significantly lower than with other welding methods, making the process suitable for only certain applications. It is used extensively in the automotive industry—ordinary cars can have several thousand spot welds made by industrial robots. A specialized process, called shot welding, can be used to spot weld stainless steel.

Stud welding is a form of spot welding where a bolt or specially formed nut is welded onto another metal part. The bolts may be automatically fed into the spot welder. Weld nuts generally have a flange with small nubs that melt to form the weld. Studs have a necked down, unthreaded area for the same purpose. Stud welding, also known as stud arc welding, joins a stud and another piece of metal together. The stud is usually joined to a flat plate by using the stud as one of the electrodes. The polarity used in stud welding depends on the type of metal being used. Welding aluminum, for example, would usually require direct-current electrode positive.