Development and problems of space frame structure application in industrial workshops (Part 1)

In our country, the space frame structure has been used in industrial plants as a special research topic for ten years. In the past ten years, hundreds of thousands of square meters of industrial plant space frame structure systems have been built across the country.

The development of the space frame structure used in industrial workshops is manifested in the continuous expansion of the application range, and it is adopted by all walks of life. For example, the space frame structure of Tangshan Gear Factory in mechanical processing is 17000m2, and the space frame structure of Shenyang Bus Factory in the automobile industry covers an area of about 25,000m2, Tangshan Locomotive and Rolling Stock Works space frame structure system system of the Ministry of Railways is nearly 50,000 m2, and nearly 70,000 m2 space frame workshops have been built in the rubber industry.

The coverage area of the industrial plant space frame structure system is getting larger and larger, gradually developing from more than 100 m2 to the large column space frame combined workshop space frame covering an area of nearly 40,000 m2. The industrial plant space frame structure system can well meet the requirements of use functions , The internal transportation tools in the workshop can be hung on the nodes of the space frame, and are not restricted by any direction. As a general workshop and a flexible workshop, this kind of large-column space frame can adapt to the needs of process changes and updates, and is welcomed by users.

Engineering practice shows that the space frame structure system is convenient for setting skylights, and can be flexibly set in various forms such as strip skylights, point skylights and triangular skylights, which can well solve the problem of ventilation and lighting.

The weight of the space frame structure system of industrial workshops is getting lighter and lighter. According to the combination of the space frame structure and the reinforced concrete roof panel, its structural weight can be reduced by about 60% compared with the reinforced concrete structure system with the same column space frame and the same service conditions. With the increase in the output of color steel plates in our country, the weight of the entire structure will be greatly reduced.

In recent years, the form of space frame structure has also begun to diversify. In addition to a large number of integral space frame, those composed of unit space frame have also been built one after another. They can be used as roof structures and floor structures. The construction speed of the space frame structure of industrial workshops has been greatly accelerated. With the accumulation of engineering practice experience and the emergence of finalized and specialized production, the design and production efficiency of the space frame structure has increased rapidly. A space frame structure of nearly 40,000 m2 only needs less Design, processing and installation can be completed within one year. Provides new experience for accelerating construction progress.

In the past ten years, we have accumulated certain experience in research, design and construction, and have made great progress. However, due to various reasons such as imperfect quality management system, the following problems also appear in the practice of space frame engineering:

1. Welding quality problems:

According to a project, the tensile test of the rods shows that the welding fails to meet the design requirements and is damaged. The damage characteristics are all broken at the weld seam at the connection between the steel pipe and the sealing plate. After inspection, most of them are due to the lack of penetration of the weld. This is not allowed for a large-area industrial plant space frame  structure, so the processing unit decisively decided that even if some bolt ball node space frame have been installed, they should be removed and reworked to ensure the welding quality. For example, a space frame project has been installed, and during the roof construction, it is found that some welds between the end of the lower chord and the sealing plate (or cone head) are broken. It was checked that the weld seam was not penetrated, which caused the weld seam to break under low stress state. Therefore, the whole space frame project had to be dismantled, the original weld seam was removed, and the weld was re-welded. During the construction of the welded ball joint space frame, it was found that the butt welds of the welded steel balls at the two hemispheres failed to penetrate in several projects.

When some projects spot-checked the welding quality of the welding joints between rods and steel balls, it was found that there were defects such as air bubbles, undercuts, slag inclusions, and incomplete penetration in the welds of some rods, all of which exceeded the quality standards stipulated in the relevant specifications and failed to meet the standards. Design requirements had to be reworked for processing. Judging from the above problems, the quality of the weld cannot be ignored. In the welded ball joint space frame, the welding of the steel pipe and the steel ball and the bolted ball joint space frame, the welding of the steel pipe and the sealing plate (or cone head), if the fillet weld is used, its strength is about 60% of the strength of the steel pipe. cannot meet the design requirements. If it is calculated according to the butt weld, the end of the steel pipe should be cut, and a certain gap should be left, and measures such as lining sleeves should be added to improve the weld forming conditions. When the thickness of the steel pipe is thin and the steel ball is thick, a small amount of fillet welds are appropriately added to the joint between the steel pipe and the steel ball for reinforcement. For thin-walled steel pipes, this measure can achieve equal strength. For the situations that thick steel pipes, although a small amount of fillet welds can be appropriately added, the number of additions should not be too large. It depends on the ratio of the thickness of the steel ball to the thickness of the steel pipe to prevent overburning of the main material. Since the weld here can only be welded on one side and cannot be cleaned, and some are unfavorable factors such as overhead welding, a reasonable welding process and an appropriate electrode should be selected for the butt weld at the end of the rod, and the current should be determined. Strictly abide by the operating procedures, and strive to minimize defects and eliminate incomplete penetration. In this way, the inspection system must be strengthened, and non-destructive testing should be carried out on important tension rods and rods with high tensile stress. When there is a suspension crane, non-destructive testing is more necessary, and it’s an important measure to eliminate hidden dangers.