The U.S. Pavilion at Osaka World Expo adopts an airless membrane structure. This quasi-elliptical exhibition hall with an axis size of 140 m*83.5 m is the first large-span membrane structure in the world, and it is the first time that glass fiber fabrics coated with polyvinyl chloride (PVC) are used. As a real modern engineering structure, the exhibition hall of Osaka World Expo marks the beginning of the era of membrane structure. Since then, membrane structure has developed rapidly all over the world. In terms of span, 234.9m*183m is the plane of air-supported air-membrane structure of "Silver Dome" in Pettiak, USA. Glass fiber fabric coated with polyvinyl chloride (PVC) has been used. Nine similar large stadiums have been built in North America. In terms of area, the suspension membrane structure of Jida Airport Hall in Saudi Arabia covers an area of 420,000 square meters. As a new form of membrane structure, cable dome was first used in gymnasium and fencing hall of Seoul Olympic Games in 1988, and then it was popularized in some sports buildings, such as "Georgia dome" of Atlanta Olympic Games in 1996, with the size of quasi-ellipse reaching 240m*193m. In order to celebrate the coming of the new millennium, Britain has built a 320m diameter "thousand dome" in London. The total area of the exhibition hall is 80,000 square meters. Covered with 72 pieces of polyvinyl chloride (PVC) coated fiberglass fabrics, the Millennium Dome, with its unique membrane structure, shows the development level of today's building technology and material science.
The development of China's modern space structure has been influenced by the advanced technology of Western countries. In recent years, there has been an active trend in the application of membrane structures. Although the initial scale of the project is small, it has gradually expanded to a larger area and span. The technology and materials used depend to some extent on foreign countries, but more projects are expected to be completed by their own efforts.
1) membrane material
Membrane structure can be widely used only after material problems have been solved. Therefore, the key problem is to provide membrane materials that meet functional requirements, good durability and economy. There are two main building fabrics for membrane structure, namely glass fiber fabric coated with polytetrafluoroethylene (PTFE) and polyester fabric coated with polyvinyl chloride (PVC). PTFE glass fiber fabric has the characteristics of high strength, translucency, fire resistance, non-flammability and good cleanliness. Although the guaranteed life of the material is 25 years, the actual service life will be longer according to the practical experience. The only disadvantage of fiberglass membranes is that they are expensive. Compared with glass fiber fabrics, PVC polyester fabrics have slightly worse strength and shorter service life, but the price is very cheap, about 1/5. In order to improve its performance, a layer of polyvinyl fluoride (PVF) or polyvinylidene fluoride (PVDF) can be added to the coating. This kind of surface can protect the fabric against the erosion of ultraviolet rays and improve its self-cleaning.
At present, many domestic manufacturers can produce PVC coated polyester fabric, but its performance has not fully met the requirements of building fabric, as a permanent building material, it needs to be further improved. Recently, some companies are trying to produce polyester fabrics and PTFE glass fibre fabrics with PVC surface layer, and their appearance and properties have been greatly improved.
2) Development prospects
From many years of practical experience at home and abroad, membrane structure has strong vitality and will be the mainstream of architectural structure development in the 21st century. It is anticipated that the most promising applications of membrane structure are:
1. Public buildings requiring natural lighting, such as gymnasiums, training rooms, exhibition halls, etc. The permeability of membranes can solve lighting problems well, save energy and give people the feeling of being in the natural environment.
2. Light and beautiful membrane structures are especially suitable for shading roofs of open or semi-open buildings. In recent years, in the stadiums of football, track and field competitions, more and more canopies adopt membrane structure. Many foreign open-air theatres and exhibition halls also use membrane as their roofs. Membrane structure can also be vigorously promoted in the agricultural market in vast areas of China.
3. The sizes of all kinds of production plants and warehouses are relatively regular, so they can be used as membrane structures and finalized and commercialized. This kind of building has the advantages of convenient transportation, disassembly and assembly, and is also very useful for emergency relief or post-disaster reconstruction.
4. In retrofitting the original buildings, the self-weight of membrane structure is a great advantage, which can be used to replace the traditional roof. It can also be used to connect adjacent houses, such as shopping malls, squares and campuses, which will effectively expand their building space.
The scale of development of membrane structure in China is very encouraging. Since 1995, only one membrane structure with an area of 3300 square meters has been built. From 1996 to 2001, an estimated 370,000 square meters of membrane structures were constructed in six years. Due to the completion of some large stadiums, the construction of membrane structures has increased at an average rate of 20% per year. The membrane structure constructed in 2003 is about 180,000 square meters. When the membrane structure was first used in Shanghai Stadium, I am afraid there is very little potential to promote the development of membrane structure. Since then, membranes have been used on stadium canopies of different sizes, and occupy a considerable share of the membrane structure. The terminal building of Guangzhou New Baiyun Airport uses membrane as part of the roof, which has a huge area of 58,000 square meters. The terminal building is likely to be another potential application of membrane structure, so it is reasonable to predict that the membrane structure in China will continue to grow at a rate of 15% to 20% per year.
Looking forward to the future, with the growth of China's economy and the continuous enrichment of cultural life, more new buildings with novel functions and forms will be built. For example, Beijing will lift its efforts for the 2008 Olympic Games. According to the plan, 32 stadiums are needed, 19 of which are newly built. The Olympic Park being planned will include national stadium, national gymnasium, National Swimming Center and international exhibition center. In addition, the 2010 World Expo will be held in Shanghai, and various types of exhibition halls will be built by countries all over the world. Most of the projects will be recruited internationally, which will certainly attract many foreign design, consultation and construction units to participate, which will undoubtedly give China new concepts and advanced technology from time to time. Because of the unique characteristics of membrane structure, it will grow on a larger scale. Through its development, China's exchanges and cooperation with the world will continue to grow.