It can be said that the long-span spatial structure is the fastest developing structural form in the last thirty years. Z.S.Makowski, editor-in-chief of the international magazine Spatial Structure, said: "In the 196s, spatial structure was still regarded as an interesting but unfamiliar non-traditional structure, but today it has been widely accepted all over the world." From today's point of view, the development of long-span and super-long-span buildings and their core spatial structure technology has become one of the important symbols representing the level of architectural science and technology in a country.
The types and forms of long-span spatial structures are very colorful, which are customarily divided into the following types: reinforced concrete thin-shell structures; Flat grid structure; Reticulated shell structure; Suspended cable structure; Membrane structure and cable-membrane structure; In recent years, the Cable Dome, which is widely used abroad, is actually a special form of cable-membrane structure. Hybrid Structure is usually the joint application of flexible components and rigid components.
among the above types of spatial structures, reinforced concrete thin-walled structures developed in China in the late 195s and early 196s. At that time, some medium-span spherical shells, cylindrical shells, hyperbolic flat shells and twisted shells were built, and a lot of efforts were put into theoretical research, and corresponding design regulations were formulated. However, this type of structure is seldom used recently, and the main reason may be that the construction is time-consuming and laborious. Flat grid structure and reticulated shell structure also include some special forms that cannot be classified separately, such as folded grid structure, multi-plane grid structure, multi-story and multi-span frame grid structure, etc., which can be called space grid structure in general. This kind of structure has developed rapidly in China, and it continues to grow. Flexible systems such as cable structure, membrane structure and cable-membrane structure all resist the action of external load by tension, which can be called tension structure. This kind of structure has a bright future. The following is a brief introduction to the development of China's spatial structure according to these two categories.
second, spatial grid structure
reticulated shell structure appeared earlier than flat grid structure. In foreign countries, the traditional rib-ring dome has a history of more than 1 years, and the first flat grid was built in Germany in 194 (using Mero system). The first batch of reticulated shells with modern significance in China was built in 195s and 196s, but the number was small. At that time, most cylindrical reticulated shells used rhombic "cube" grid system. The steel reticulated shell of Tianjin Gymnasium (span 52m) built in 1956 and the reinforced concrete reticulated shell (span 4m) built in Tongji University in l961 can be taken as typical representatives. The spherical reticulated shell mainly adopts the ring-assisted system. The hemispherical dome of Chongqing People's Auditorium (span 46.32m) built in 1954 and the circular steel roof of Zhengzhou Gymnasium (span 64m) built in 1967 are the only two large-scale spherical reticulated shells. Since then until the early 198s, reticulated shells have not been further developed in China.
relatively speaking, since the first flat grid structure (ball room of Shanghai Normal University, 31.5mx4.5m) was built in 1964, the grid structure has maintained a good development momentum. The Capital Gymnasium, which was built in 1967, adopted an oblique orthogonal grid structure, with a rectangular plane size of 99mx112m and a thickness of 6m. It was connected by steel members and high-strength bolts, and the steel index was 65kg per square meter (1kg per square meter ≈9.8pa). The Shanghai Gymnasium for 1, people, which was built in 1973, adopts a circular plane three-way grid with a net frame of 11m and a thickness of 6m, and adopts circular steel tube members and welded hollow spherical joints, with a steel index of 47kg per square meter. At that time, the flat grid was still a brand-new structural form in China, and both grids were relatively large in scale, which was still representative even today, thus having a great impact on the engineering field. Encouraged by the demand of gymnasium construction at that time, domestic universities, research institutions and design departments invested a lot in this new structure, and professional production and installation enterprises also gradually grew, laying a solid foundation for the further development of this structure. The ten years since the reform and opening up have been the golden period of the rapid development of China's spatial structure, and the flat grid structure is naturally in the priority position of getting ahead of others. Even in the late 198s, most of the sports buildings built in Beijing to welcome the 199 Asian Games still used flat grid structure. During this period, computers have been widely used in the design of grid structures, and the production technology has also made great progress. Assembled bolt-ball joints have been widely used, which greatly accelerated the installation of grid structures.
but there are always two sides to everything. At the same time of accelerating the development of flat grid structure, with the expansion of economic and cultural construction demand and the improvement of people's appreciation of architecture, designers increasingly feel that the choice of structural forms is limited when designing an increasing number of long-span buildings, which cannot meet the growing requirements for architectural functions and architectural modeling diversification. This realistic demand has played a good role in stimulating the development of various spatial structure forms such as reticulated shell structure and suspended cable structure. Because the production conditions of reticulated shell structure and grid structure are the same, the domestic foundation has been ready. Therefore, since the second half of the 198s, when the corresponding theoretical reserves and design software were initially complete, reticulated shell structure began to develop rapidly under the new conditions. The number of construction is increasing year by year, and various forms of reticulated shells, including spherical reticulated shells, cylindrical reticulated shells, saddle reticulated shells (or twisted reticulated shells), hyperbolic flat reticulated shells and various special-shaped reticulated shells, as well as their combinations, have been applied; New structural systems such as prestressed reticulated shell and cable-stayed reticulated shell are also developed. In recent years, some large-scale reticulated shells have been built. For example, Tianjin Gymnasium, which was built in 1994, adopts double-layer spherical reticulated shell with ribbed ring and inclined rod (Schwedler type). Its circular plane has a clear span of 18m, and its periphery protrudes 13.5m m. The thickness of the reticulated shell is 3 m. It adopts circular steel tube members and welded hollow spherical joints, and the steel index is 55kg per square meter. The Heilongjiang Provincial Speed Skating Hall, which was built in 1995, is used to cover the 4m speed skating track. Its huge double-layer reticulated shell structure consists of a central cylindrical shell and hemispheric shells at both ends, with an outline size of 86.2mx191.2m, covering an area of 15, square meters and a reticulated shell thickness of 2.1m m. It is made of round steel tube members and bolt ball joints, and the steel index is 5kg per square meter. The plane of Changchun Gymnasium for 1, people, which was just built in 1997, is in the shape of a peach pit. It is made up of ribbed ring-shaped spherical reticulated shell with the central strip cut off and then assembled. If the outriggers are counted, the outline size is 146mx191.7m, and the thickness of the reticulated shell is 2.8m m. The upper and lower chords and web members of its truss-type "mesh" are all square (rectangular) steel pipes, which are welded together. It is the first square steel pipe network in China. The design scheme of this reticulated shell structure was put forward by foreign countries, and the construction drawing design, fabrication and installation were completed in China.
with the increasing application of reticulated shell structure, the flat grid structure has not stopped its own development. This simple structure at present has its own wide range of use, regardless of the size of the span; In recent years, it has expanded its application scope in some important fields. For example, in the aspect of airport maintenance hangar, large hangars such as Guangzhou Baiyun Airport 8m hangar (1999), Chengdu Airport 14m hangar (1995) and Capital Airport 2Zmx15m hangar (1996) all adopt flat grid structure. These three-sided supported flat grid structures are huge in scale and need to bear heavy suspension loads, and often use heavy welded steel (or steel pipe) structures, and sometimes need to use three-layer grid structures; Its steel index per unit area can reach twice or more than that of the grid used in general public buildings. Single-storey industrial workshop is also an important field in which flat grid structures have developed rapidly in recent years. In order to arrange the production process flexibly, the column grid size of the factory building tends to expand day by day, and then the flat grid structure becomes a very economical and applicable ideal structural scheme. In 1991, the golf car installation workshop of the First Automobile Factory was built, covering an area of nearly 8, square meters (189.2mx421.6m), with a column grid of 21mx12m, and a welded ball joint grid with a steel index of 31kg per square meter. This workshop is the largest flat grid structure in the world at present. Tianjin Seamless Steel Pipe Factory, which was built in 1992, has a workshop area of 6, square meters (18m x 564m) and a column grid of 36m x 18m, and adopts a grid structure with bolted ball joints, with a steel index of 32kg per square meter. Compared with the traditional plane steel truss scheme, it saves 47%. In view of the huge circular product of such workshops, they do provide a broad new field for the development of flat grid structures. Obviously, the spatial grid structure, including grid structure and reticulated shell, is the fastest developing and most widely used spatial structure type in China in recent ten years. This kind of structural system has good overall stiffness, superior technical and economic indicators, and can provide rich architectural shapes, so it is loved by builders and designers. The vigorous development of grid enterprises in China also provides convenient production conditions for this kind of structure. It is estimated that in recent years, the space truss and reticulated shell structure built in China has reached 8 million square meters of construction area every year, and the corresponding steel consumption is about 2, t. Such a large number is unmatched by any other country, and it is worthy of the title of "the kingdom of grid". It is no wonder that relevant foreign enterprises are drooling over this huge market.
such a great development momentum will naturally bring some problems. Compared with the international level, there is still a certain distance between the technology level and quality management level of grid production in China. Especially, driven by market demand, a large number of small grid enterprises have mushroomed, and it is inevitable that the good and the bad are mixed, and the design is not always served by experienced people. Therefore, it is an important task to strengthen industry management and grasp the quality of design, manufacture and installation to promote the further healthy development of China's spatial structure.
III. Tension Structure
The development of modern cable structures in China began in the late 195s and 196s, and the Workers' Gymnasium in Beijing and the Zhejiang People's Gymnasium in Hangzhou were two representative works at that time. Beijing Workers' Gymnasium was built in 1961, and its circular roof adopts a spoke double-layer suspension cable system with a diameter of 94m. Zhejiang People's Gymnasium was built in 1967. Its roof is an elliptical plane with a long diameter of 8m and a short diameter of 6m．. It adopts hyperbolic paraboloid orthogonal cable net structure.
The earliest modern cable-stayed roof in the world is Raleigh Gymnasium, which was built in the United States in 1953. It adopts saddle-shaped orthogonal cable net with two oblique parabolic arches as edge members. The above two cable structures built in China can be said to have reached the international advanced level at that time in terms of scale or technical level. However, since then, the development of cable structures in China has stopped for a long time. Until the 198s, due to the development of long-span buildings, the demand for diversification of spatial structure forms has aroused people's enthusiasm again, the number of engineering practices has increased greatly, and the theoretical research on the diversification of application forms has been carried out accordingly.
The flexible suspension cable not only has no stiffness in the natural state, but also its shape is uncertain. Measures such as laying a heavy roof or applying prestress must be taken to give it a certain shape and become a structure with necessary stiffness and shape stability under external load. It is commendable that while learning and absorbing advanced foreign experience, Chinese scientific and technical personnel have made many attempts and innovations in creating structural application forms that are more in line with China's national conditions in combination with specific engineering conditions.
in order to improve the shape stability of single-layer suspension cables, it is also very effective to set transverse stiffening beams (or trusses) on single-layer parallel cable systems. The transverse stiffening member has two functions: one is to transfer the possible concentrated load and local load to distribute it more evenly to the parallel cables; Secondly, the whole system is prestressed by pressing the two ends of the transverse stiffening member to the predetermined position or by tensioning the cable, so as to improve the rigidity of the roof. From the practice of several projects such as Anhui Gymnasium, this mixed structure system is a successful creation with convenient construction and economical materials.
The prestressed double-layer cable system composed of a series of load-bearing cables and stable cables with opposite curvatures is another effective form to solve the shape stability of suspended cable structures. Its working mechanism is similar to that of prestressed cable net. In 1966, Jawerth, a Swedish engineer, first adopted a patented system called "cable truss" consisting of a pair of load-bearing cables and stabilizing cables in Stockholm Skating Hall. Later, this plane double-layer cable system was widely used in various countries. This system has also been adopted in Wuxi Gymnasium in China. As an improvement of this system, Jilin Skating Hall adopted a new type of spatial double-layer cable system, whose load-bearing cables and stabilizing cables are in different planes, but staggered by half a column distance, thus creating a novel architectural shape and solving the roof drainage problem commonly encountered in rectangular plane suspended cable roofs. This novel structure participated in the international advanced structure exhibition held in the United States in 1987.
another feature of the development of cable structures in China is the use of various combination means in many projects. The main way is to combine more than two prestressed cable nets or other suspension cable systems, and set strong arch or rigid frame structures as intermediate supports to form various forms of combined roof structures. For example, the roofs of Sichuan Gymnasium and Qingdao Gymnasium are composed of two cable nets and a pair of reinforced concrete arches as intermediate supports. Beijing Chaoyang Gymnasium consists of two cable nets and a central supporting structure called "cable arch system". The central cable-arch system is composed of two suspended cables and two steel arches, which is a mixed structure itself, and its concept is also innovative. The use of various combined roofs not only further enriches the architectural modeling, but also can better meet some functional requirements of buildings, such as providing "optimal" internal space for gymnasium buildings. From a purely technical and economic point of view, a single cable net or other suspended cable system can span a large span economically, and it is not necessary to adopt an intermediate supporting structure. Therefore, the use of combined roof in many occasions is mainly due to architectural modeling and functional considerations. Judging from the practical effect of our country in recent years, it has played an expected role in this respect.
A series of mixed structural forms can be formed by introducing the cable-stayed system into the roof structure. This system provides a series of intermediate elastic supports for the span structure (main beam, truss, flat grid, etc.) of the roof by using stay cables extending from the top of the tower column, so that these span structures can span a large span without increasing the height of the structure and the cross section of the members. The cable-stayed reticulated shell mentioned above also belongs to this kind of mixed structure.
Although the suspended cable structure has made gratifying progress in the past ten years, its development is relatively slow compared with the grid structure and reticulated shell structure. There may be two reasons: (1) The design and calculation theory of suspended cable structure is relatively complicated, and there is a lack of practical calculation program with a high degree of commercialization, so it is difficult for general design units to adopt it; (2) Although the construction of suspended cable structure is not complicated, the general construction units are not familiar with it, and there is no professional construction team for suspended cable structure, which also affects the construction units and design units to boldly adopt this structural form.
at the same time, both belong to the tension structure system,