It is a long strip of steel with an I-shaped cross section. I-beams are divided into ordinary I-beams and light I-beams. It is a section steel with an I-shaped cross-section. Whether the I-shaped steel is ordinary or light, because the cross-sectional size is relatively high and narrow, the moment of inertia of the two main axes of the cross-section is quite different, so it can only be directly used for members that are bent in the plane of its web or formed into a lattice-type force-bearing member. It is not suitable for axial compression members or members with bending perpendicular to the web plane, which limits its application range.