I-beam is mainly divided into ordinary I-beam, light I-beam and low alloy light I-beam. Ordinary I-beam and light I-beam flanges are thick on the web plate and thin on the outside. Ordinary I-beam, light I-beam, because the cross-sectional dimensions are relatively high, narrow, so the section of the two main sleeve moment of inertia difference is large, which makes it in the scope of application has a great limitation. The use of I-beam shall be selected according to the requirements of the design drawings.