On August 8, 2008, when Li Jiulin, the chief engineer of the National Stadium, watched 29 fireworks ‘footprints’ march along Beijing’s central axis toward the National Stadium, he let out a long breath.This super-large steel stadium project, which was the largest in the world at the time, used the most steel, and had the most complex structure, has finally been unveiled to the world.The whole world is watching a steel miracle called the ‘Bird’s Nest’.This building, woven from 42,000 tons of steel, has become a milestone in the development of steel structures in China.
At the time, few people may have realized that this was not just the success of an opening ceremony, but the beginning of the era of steel structure buildings in China.
Sixteen years later, when the torch of the Winter Olympics is lit in Beijing again, a vibrant ‘Ice Ribbon’ once more showcases a new leap in China’s steel structure technology. From the ‘Bird’s Nest’ to the ‘Ice Ribbon,’ these two iconic venues witness a remarkable evolution in China’s steel structure construction.
01 Bird’s Nest: A Milestone in China’s Steel Structures
The appearance of the ‘Bird’s Nest’ broke the traditional square and upright image of Chinese architecture. On December 24, 2003, the National Stadium officially began construction, ushering in a new era of steel structure buildings in China.
This top-class sports building is 333 meters long from north to south, 294 meters wide from east to west, and 69 meters high. The main structure is designed for a service life of 100 years and is built to withstand an earthquake intensity of level 8.
The most revolutionary breakthrough of the ‘Bird’s Nest’ lies in its unique structural design. Its exterior structure is primarily composed of a massive portal steel frame, with no internal columns, and the high-altitude, large-span saddle-shaped roof rests on 24 truss columns. This means that the stress from 42,000 tons of steel is concentrated on just these 24 columns and their foundations. Such a massive load cannot be supported by ordinary steel.
The construction team faced a tricky problem: the unique and innovative design of the ‘Bird’s Nest’ structure required a special type of steel—Q460 low-alloy high-strength steel.The strength of this steel is twice that of ordinary steel, with a yield strength of up to 460 MPa, meaning it will only undergo plastic deformation when subjected to an external force of 460 MPa.At that time, there was no domestically produced high-strength steel that met the requirements, and it was difficult to import from abroad. Faced with these challenges, Chinese engineers did not back down. After countless trials and research, they eventually produced domestic Q460 steel, which became the backbone of the ‘Bird’s Nest’ stadium.
The challenges of the ‘Bird’s Nest’ steel structure project are not limited to the materials. Its roof has a hyperbolic saddle shape, and the total weight of the roof steel structure is about 14,000 tons. The steel structure installation used a high-altitude scattered assembly method, with 78 temporary supporting towers set up in three concentric circles—inner, middle, and outer—during installation. For such a large-span open-space saddle-shaped steel structure, the design, construction, and unloading methods of the support system are key aspects of the project.
Before the ‘Bird’s Nest,’ most buildings in China were square and angular, but turning this highly creative design into reality meant overcoming challenges at every step. During construction, the team developed over 520 construction and technical plans, held more than a hundred expert technical reviews, and completed over 20,000 detailed design drawings. At that time, BIM (Building Information Modeling) technology was used for the first time in China, using cutting-edge technology of the era to transform the designers’ ‘concept drawings’ into a three-dimensional ‘digital Bird’s Nest.’
02 Technological Evolution: From the ‘Bird’s Nest’ to the ‘Ice Ribbon’
If the ‘Bird’s Nest’ represented the beginning and breakthroughs of Chinese steel structures, then the venues of the 2022 Beijing Winter Olympics showcased the maturity and leap forward of Chinese steel structures.
As the iconic venue of the Beijing Winter Olympics, the National Speed Skating Oval, known as the ‘Ice Ribbon,’ although like the ‘Bird’s Nest’ primarily built with steel, follows a very different technical path. The National Stadium weaves steel into a ‘Bird’s Nest’ structure, while the National Speed Skating Oval uses steel cables to ‘stretch’ out the large-span roof of the ‘Ice Ribbon.’
The cable-net roof of the ‘Ice Ribbon’ is the largest single-layer bidirectional orthogonal saddle-shaped cable-net roof in the world of sports stadiums, with a maximum span of 198 meters by 124 meters, yet it uses only a quarter of the steel required by traditional roofs.
The key material for ‘weaving the canopy’ is a type of closed steel wire rope called ‘high-vanadium closed cable.’ At that time, factories capable of producing this construction material were mainly concentrated in developed countries in Europe and America, and there was no precedent for it domestically.After numerous rounds of technical breakthroughs, the team ultimately mastered the processing and application technology of the Z-shaped steel wires, which are the core of high-vanadium sealed strands, and successfully woven the “ice ribbon,” the largest net in the world.
The advancement of digital technology is also a major highlight of the ‘Ice Ribbon.’ Due to the highly complex spatial form of the cable-net roof, each ‘grid’ has a different shape after tensioning. The size of each infill unit also varies and requires data obtained through actual measurements before being customized. All of this relies on the support of the building’s digital information BIM system.From the 8,500-ton steel structure to each uniquely shaped curtain wall glass and the differently curved stands, everything on the ‘Ice Ribbon’ has been digitized.
Since then, domestically-produced high-vanadium sealed cables have not only been used in major construction projects nationwide but have also been exported for use in significant international construction projects.
03 Steel Structure Buildings: From Landmarks to Everyday Norms
The development of steel structure buildings in China has gone through a process from nothing to widespread use, from being rare to becoming common. Looking back at history, the path of steel structure development in China has not been smooth. According to the development history of China’s building steel structures, the development of complex building steel structures in our country can be roughly divided into three stages:
The first phase was in the 1990s, represented by projects such as the Shanghai Grand Theatre, using welded box and steel tube truss structures with complex constructions.
The second phase was from 2000 to 2010, marked by the construction of projects like the National Stadium, during which complex architectural steel structures entered a period of rapid development.
The third phase is the past decade, during which innovations in technology have led to a proliferation of various complex steel structures, such as the Shanghai Tower.
The beginnings of modern steel structure architecture in China can be traced back even earlier. In 1985, ten welders from China State Construction Third Bureau went to Japan to study and mastered the then world-leading carbon dioxide gas shielded welding technology.
After returning to China, they built the ‘First Steel Building of China,’ the Shenzhen Development Center, ushering in the era of modern steel-structured buildings in the country. In 1995, this team built the ‘Tallest Building in Asia,’ the Shenzhen Diwang Building.
The ‘Bird’s Nest’ project is at a critical point in the development of steel structure technology in China. It is not just a technological breakthrough, but also a conceptual innovation. As architect Li Xinggang stated, an important aspect of the design concept of the ‘Bird’s Nest’ is that ‘structure is form,’ meaning that the architectural form naturally generated by the structure is closely connected with its internal spaces.
04 Green Transition: Sustainable Development of Steel Structures
From the ‘Bird’s Nest’ to the ‘Ice Ribbon,’ the development of steel structures in China is reflected not only in technological advancements but also in the deepening of green and sustainable concepts.
The construction of venues for the Beijing Winter Olympics fully reflects the concept of a green and low-carbon Olympics. All main materials used in the construction of the venues and their supporting projects are high-quality steel with high strength, toughness, and corrosion resistance. The ‘Ice Ribbon’ is a model of a green Olympics. As the first speed skating venue in Winter Olympic history to use carbon dioxide as a refrigerant, its stainless steel cooling pipes beneath the ice total 120 kilometers in length. According to competition requirements, the temperature difference across the entire ice surface must be controlled within 0.5 degrees Celsius, which places very high demands on the precision of the steel processing.
As an early representative, the ‘Bird’s Nest’ has also shown consideration for green and environmental protection. During its construction, the National Stadium adopted advanced energy-saving designs and environmental measures, such as effective natural ventilation and lighting, comprehensive rainwater recycling, the use of renewable geothermal energy, and the application of solar photovoltaic power technology.
Today, we wandered through Beijing Olympic Park, gazing up at the heavy steel woven structure of the ‘Bird’s Nest’, then contemplating the light cable-net roof of the ‘Water Cube’, as if reading a history of the evolution of China’s steel structure technology.
As iconic buildings of Beijing, the ‘Bird’s Nest’ and the ‘Ice Ribbon’ embody not only architectural functionality and artistic beauty, but also the spirit of Chinese engineering innovation, showcasing Chinese aesthetics and stories to the world.