1. The upper chord of steel frame is a name for the upper bar in steel structure, such as grid structure, truss structure and some pipe racks. For example, the upper flange, lower flange and web of steel columns are mostly used in grid structures. Upper chord and upper (lower) chord refer to roof trusses and trusses. The long one above is called the upper chord, the longest one below is called the lower chord, and the short ones in the middle (vertical and oblique) are called web members. For example, for a triangular or trapezoidal roof truss, the top two (as the saying goes, eight-character beams) are called the top chord, and the horizontal one below is called the bottom chord. The top chord of roof truss is compression bar, and the bottom chord is tension bar.
2. Horizontal support of upper chord. (A rigid frame is formed in the upper chord plane of the roof truss to enhance the overall rigidity of the roof, ensure the stability out of the plane of the upper chord of the roof truss or the upper flange of the roof beam, and at the same time transfer the wind load from the wind-resistant column to the top of the longitudinal bent column.
3. The lower chord is horizontally supported. Lower chord horizontal support includes lower chord horizontal support and longitudinal horizontal support. Vertical support of roof refers to the support arranged between roof trusses (or roof beams).