Development of Long-Span Spatial Structure (Ⅱ)

The appearance of reticulated shell structure is earlier than that of plane grid structure. In foreign countries, the traditional rib-ring dome has a history of more than 100 years. In 1940, the first plane grid was built in Germany (using Mero system). The first batch of reticulated shells with modern significance in China was built in 1950s and 1960s, but the number is small. At that time, most cylindrical reticulated shells used rhombic "cube" grid system. The steel reticulated shell of Tianjin Gymnasium (span 52m) built in195 and the reinforced concrete reticulated shell of Tongji University (span 40m) built in 196 1 year are typical examples. The spherical reticulated shell mainly adopts the ring auxiliary system. The hemispherical dome of Chongqing People's Hall (span 46.32m) built in 1954 and the circular steel roof of Zhengzhou Gymnasium (span 64m) built in 1967 are the only two large spherical reticulated shells. Since then, until the early 1980s, reticulated shells have not been further developed in China.

Relatively speaking, since the first plane grid structure was built in 1964 (Shanghai Normal University Ball Room, 3 1.5mx40.5m), the grid structure has maintained a good development momentum. The Capital Gymnasium, built in 1967, adopts an oblique grid structure, with a rectangular plane size of 99mx 1 12m and a thickness of 6m. Connected by steel members and high-strength bolts, the steel index is 65kg per square meter (per square meter 1kg≈9.8 pa). The Shanghai Gymnasium for 10,000 people built in 1973 adopts 1 10m circular plane three-dimensional grid truss with a thickness of 6m. Circular steel tubular members and welded hollow spherical joints are adopted, and the steel consumption index is 47kg per square meter. At that time, the flat grid was still a brand-new structural form in China, and both of them were relatively large in scale, which was still representative even today, thus having a great influence in the engineering field. Encouraged by the demand of gymnasium construction at that time, domestic universities, research institutions and design departments invested a lot of money in this new structure, and professional production and installation enterprises gradually grew up, laying a solid foundation for the further development of this structure. More than ten years since the reform and opening up have been the golden period of the rapid development of China's spatial structure, and the plane grid structure is naturally in a priority position. Even in the late 1980s, most of the sports buildings built in Beijing to welcome the 1990 Asian Games still used plane grid structure. During this period, computers are widely used in the design of grid structure, and the production technology has also made great progress. The wide application of assembled bolt-ball joints has greatly accelerated the installation speed of grid structure.

But there are always two sides to everything. While accelerating the development of plane grid structure, with the expansion of the demand for economic and cultural construction and the improvement of people's appreciation of architecture, designers feel more and more restricted in the choice of structural forms when designing more and more long-span buildings, which can not meet the growing requirements of 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 done. Therefore, since the second half of 1980s, when the corresponding theoretical reserves and design software were initially completed, reticulated shells began to develop rapidly under 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 and their combinations, have been applied; New structural systems such as prestressed reticulated shells and cable-stayed reticulated shells have also been developed. In recent years, some large reticulated shells have been built. For example, Tianjin Gymnasium, which was built in 1994, adopted a double-layer spherical reticulated shell with ribbed ring diagonal bars (schwedler type). Its circular plane has a clear span of108m, its periphery extends to13.5m, the thickness of the reticulated shell is 3m, it is composed of circular steel tubular members and welded hollow spherical joints, and the steel index per square meter is 55kg. Heilongjiang speed skating hall, built at 1995, is used to cover the 400-meter speed skating track. Its huge double-layer reticulated shell structure consists of a central cylindrical shell and hemispheric shells at both ends, with an overall dimension of 86.2mx 19 1.2m, a coverage area of15000m2 and a reticulated shell thickness of 2.1m.. It consists of circular steel tube members and bolt balls. 1997 The newly-built Changchun 10,000-person gymnasium is shaped like a peach pit, which is formed by cutting off and splicing the central belt of a ribbed annular spherical reticulated shell. If the outrigger is included, the overall dimension is146mx191.7m, and the thickness of the reticulated shell is 2.8m The structural design scheme of the reticulated shell was put forward by foreign countries, and the construction drawing design, fabrication and installation were all completed in China.

With the more and more applications of reticulated shells, the planar grid structure has not stopped its own development. This simple structure has a wide range of uses at present, regardless of the size of the span; In recent years, it has expanded its application in some important fields. For example, in the aspect of airport maintenance hangar, the 80m hangar of Guangzhou Baiyun Airport (199), Chengdu Airport 140m hangar (1995) and Capital Airport's 2zmx 150m hangar (1996) all adopt plane grid structure. These flat grid structures supported on three sides are large in scale and need to bear heavy suspension loads, and often adopt heavy welded steel (or steel pipe) structures, and sometimes need to adopt three-layer grid structures; Its steel consumption 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 with rapid development of flat grid structure 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, so the plane grid structure becomes a very economical and applicable ideal structural scheme. 199 1 the golf car installation workshop of the first automobile factory, covering an area of nearly 80,000 square meters (189.2mx42 1.6m), with a column grid of 2 1mx 12m, and welded ball joint grids per square meter. This workshop is the largest plane grid structure in the world at present. Tianjin Seamless Steel Pipe Factory, built in 1992, covers an area of 60,000 square meters (108m×564m), with a column grid of 36m×18m. It adopts a grid structure with bolted ball joints, and the steel consumption index is 32kg per square meter, saving 47% compared with the traditional plane steel truss scheme. In view of the huge round products in this workshop, they really provide a broad new field for the development of plane grid structure. Obviously, spatial grid structure, including grid structure and reticulated shell structure, is the fastest developing and most widely used spatial structure type in China in recent ten years. This 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 China's power grid enterprises also provides convenient production conditions for this structure. It is estimated that in recent years, China has built 8 million square meters of grid and reticulated shell structures every year, and the corresponding steel consumption is about 200,000 t, which is incomparable to any other country and worthy of the title of "grid kingdom". No wonder foreign companies 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 technical level and quality management level of power grid production in China. Especially, driven by market demand, a large number of small power grid enterprises have sprung up like mushrooms after rain, which inevitably leads to mixed quality, and the design is not always served by experienced people. Therefore, strengthening industry management and paying attention to the quality of design, manufacture and installation is an important task to promote the further healthy development of China's spatial structure.