Water Cube” Structure Revealed

The “Water Cube” of the National Aquatics Center in the Olympic Park has 17,000 standard seats, of which about 13,000 are temporary seats and 4,000 are permanent seats. During the Olympic Games, it will be used for swimming, diving, synchronized swimming, water polo and other competitions. Its main structure is designed to have a service life of 100 years.

The project was awarded the name [H2O]3 “Water Cube” (Water Cube), which is said to be inspired by “a square box”, many “water bubbles” and many “water molecules”.

Appearance design and polyhedral ductile steel frame structure of “Water Cube”:

From the outside, the whole “Water Cube” looks like a blue-colored “square box”, with an overall construction area of about 80,000 square meters and a height of about 30 meters, and the exterior wall of the building is made of a new type of environmentally friendly and energy-saving ETFE (ethylene tetrafluoroethylene) membrane material, consisting of more than 3,000 air pillows. ETFE (ethylene tetrafluoroethylene) membrane material, composed of more than 3,000 air pillows, unfolding an area of 110,000 square meters. These pillows mimic the bubbles of nature’s liquids and vary in size. It takes about two to three hours to install an air pillow from factory cutting to complete installation.

From the microstructure of water molecules and water bubbles, the designer deduces a new type of rigid structural system, and the ETFE transparent film covering the surface gives the building an ice crystal-like appearance. The square shape represents one of the most simple concepts of the Chinese people, and also from the perspective of urban planning, the city of Beijing has evolved from a square shape into a city, and in this pattern, the square shape represents the wisdom of people. In addition, our understanding of water is that it is serene on the outside, but contains many variable possibilities, which is a characteristic of water. Its color reflects the expression of the surrounding nature, making the building itself very rich.

The membrane structure building form used in the program is a brand new building form that is most representative of the 21st century, and so far it has become one of the main forms of large-span space building. It integrates architecture, structural mechanics, fine chemistry, material science and computer technology to build a landmark space structure form, which not only embodies the beauty of the power of the structure, but also fully expresses the architect’s vision to enjoy the romantic space of nature. The membrane structure was perfectly embodied in the architectural design of the 2008 Olympic Games.

The most moving visual effect of the Water Cube is that no matter from any angle inside or outside the venue, you can see a closely connected translucent water bubble, and not see a redundant steel beams. So, how do the water bubbles and steel beams become one? More than a hundred years ago the scientist Rod. Colvin put forward this “bubble theory”. He said, in fact, the arrangement of the structure of many substances in nature, are composed of this bubble structure, it is said that this bubble theory is to solve the “Water Cube” structural problems based on.” Water Cube” the entire components are 20,000 rods, 10,000 balls, a total of 30,000 components to form such a structural system. Each node, each rod is different.

The wall and roof structure of the National Aquatics Center “Water Cube” creatively adopts a new type of polyhedral space rigid frame structural system, which uses rectangular steel tubes for the chords, round steel tubes for the webs, and welded ball nodes for the nodes. Although the composition of the structure is similar to the space frame structure, the stress condition of the structural members is completely different from that of the space frame structure of the two-force rods, which is similar to the stiffened beams of the hollow web space frame. The internal forces of the members include bending moment, axial force, shear force and torsion, and the bending stress is larger than the axial stress, so the optimization of the structure is more complicated. Optimization in structural design calculations, including: “strong wall and weak cover” optimization, wall members and roof members choose different stress level control; section type optimization, give up the stiffened rib section and use compact section, give full play to the section plasticity, improve structural ductility; geometric composition of the “hybrid” optimization, the lower chord of the cover through the inner wall, in order to reduce the excessive bending stresses of the bars at the junction of the cover and the wall and the additional a small number of The geometric composition of “hybrid” optimization, the roof chord through the inner wall, in order to reduce the excessive bending stress of the roof and wall junction of the rod attached to a small number of web, the formation of a local confluence force system; ‘articulation’ optimization, the use of articulation computation processing strategy, a small number of large bending stresses can not meet the specification requirements of the rod at both ends of the treatment of the articulation, to strengthen the relevant rods around, and then the iterative calculation of the rigid connection to meet the requirements of the bearing capacity; “strong nodes and weak rods” optimization, to improve the structural ductility, to ensure that the rod end of the weld destruction is later than the yielding of the rods.

The key to stacking a single bubble into a wall is to find the exact location of the steel beams that serve as the edges of the bubbles. The engineers tried many things, including GPS positioning, laser positioning, panning, and installing in different areas, but the problem persisted! It is said that the “hero” comes from an experienced veteran worker fiddling with a few matches when he thought of a good way: first by a point and a rod to determine a plane, and then the other rods can be basically accurate by visual inspection of the location of the rod to determine. The idea is to make an adjustment, do not think of building a ball first, if you first build a ball of a surface first, the other several surfaces in the same way, will also be quickly built, so that a sphere is naturally formed. The use of high school geometry, a line and a point outside the line, to determine a plane. The master worker solved the big problem in this way. This type of structure is now called polyhedral space steel frame structure. This kind of structure in the past, not only in our country, in the world is still not, such a kind of the world’s first water cube swimming pool this kind of structural form, is our China to realize. This working method created by the master workers, together with the construction theory of the engineers, has been written into the technical regulations for the construction management of polyhedral ductile steel frame structure, for which our country has complete independent intellectual property rights.

In order to present a three-dimensional design animation in the “Water Cube” kind of effect, the air pillows need to be inflated after installation. This process is completely monitored by the “Water Cube” computerized automatic inflation system, the system can be based on the prevailing air pressure, light and other conditions to control the inflation status of each air pillow. Although the membrane structure of “Water Cube” is a unified whole in appearance, each air pillow is relatively independent. Therefore, even if one of them is damaged, it will not cause the “Water Cube” as a whole “deflation”. Moreover, it is very convenient to replace the damaged air pillows.