cold roll forming is widely used in foreign construction industry. It is used as roof trusses, purlins, trusses, rigid frames, wall frames, keels, roof slabs, wall panels, slabs, doors and windows, and even containers, pipes, cofferdams, steel sheet piles, and breakwaters. Wait. In recent years, reticulated shells, shelves, single-storey and multi-storey houses with cold-formed steel have also developed rapidly, from airports to large shopping centers.From office buildings to stadiums, from convention centers to residential buildings, cold-formed steel products are widely used architectural design materials. In developed countries, the construction industry is the largest user of cold-formed steel, cold-formed steel accounts for 5% of total steel, and cold-formed steel for construction accounts for about 70% of cold-formed steel. Cold-formed steel products are used in construction. The main business is cold-formed rectangular tubes for structural use and cold-formed steel for construction. From the structural mechanics and economic point of view, the combination of cold-formed steel and H-shaped steel is the best combination in the construction industry, which can realize the industrialization of industrial plants and residential buildings.In Japan, before 1980, Japan produced only square rectangular tubes of 200 mm*200 mm or less and a small number of open-formed cold-formed steels. The Japanese steel-structured residential center columns were all H-shaped steel. After the Sendai earthquake in Japan in 1984, it was found that the weld between the column and the beam was easily cracked by the study of the damaged steel structure in the Sendai earthquake. The reason was that it was limited by the shape and structure of the H-shaped steel. H-beam butt welding with too few welds. Therefore, Japan revised the construction law after 1984, stipulating that Japanese steel-structured residential columns must use square rectangular tubes to increase the length of the welds, thereby improving the seismic resistance of the houses. With the popularization of cold-formed steel in the application of building steel structures, the specifications for cold-formed steel production have also increased. At present, the square rectangular tube has a maximum specification of 550 mm * 550 mm and a maximum wall thickness of 22 mm. In 2002, the total output of cold-formed rectangular tubes for steel structures in Japan reached 2 million tons. At present, the steel pipe with the largest market demand is (200 mm * 200 mm) ~ (400 mm * 400 mm). These specifications have a cold-form rectangular tube covering more than 80% of the total square and rectangular tubes used in Japanese steel structures. Specifications products account for less than 10% of the market.In the United States, the survey data show that the amount of cold-formed rectangular tubes and hot-rolled H-beams used in the construction industry is about 1:1. In the 1990s, the proportion of cold-formed steel used in construction steel structures exceeded even The amount of hot rolled H-beam. Among them, cold-formed welded pipes (including square rectangular pipes and original pipes) account for about 25% of the steel used for construction steel structures. In addition, the United States imports a certain number of structural steel pipes every year. World Steel Statistics Monthly Report! Statistics for the 7th issue of 2003. In May 2003, the US imported steel pipe for structural use was 28 728 tons, and the cumulative import from January to May was 164 210 tons, an increase of 10% over the same period of 2002. The proportion of various cold-formed steels in the United States in steel for construction steel structures is also over 20%.