There are mainly four types of U-shaped steel produced in China: 18U, 25U, 29U and 36U. However, U18 is seldom produced because of its low carrying capacity. In GB/T 4697-2008, in addition to the four types of U-shaped steel in Shangzhu, another 40U model was added. Channel steel can be divided into ordinary channel steel and light channel steel. And according to the shape, it can be divided into four kinds: cold-formed equal-side channel steel, cold-formed unequal-side channel steel, cold-formed inner-side channel steel, cold-formed outer-side channel steel.