1. Layout of Bracing
In bays where column bracing is installed, roof transverse bracing should also be provided to form a geometrically stable system. The arrangement of column bracing shall be determined based on factors such as the longitudinal column spacing of the building, loading conditions, and temperature sections.
For buildings without cranes, the spacing between column bracing should preferably be 30m to 45m. The end column bracing should be placed in either the first or second bay from the end of the building.
For buildings with cranes, the bracing below the crane corbel should be located near the middle of the temperature section. If the temperature section is relatively long, the bracing should be placed within the third points, and the spacing between bracing shall not exceed 50m. The principles for arranging bracing above the crane corbel are the same as those for column bracing in buildings without cranes.
2. Cross-Section and Construction Details of Column Bracing
Column bracing is classified as either flexible or rigid, depending on whether the diagonal members can effectively resist axial compressive forces. For buildings equipped with overhead cranes, rigid bracing is required.
Rigid bracing can be made from hot-rolled steel sections such as angles, channels, I-beams, or steel tubes. Both ends of the bracing members are pin-connected to the columns via gusset plates. The inclination angle between the rigid bracing and the ground should be controlled between 30° and 60°, with an angle close to 45° being preferable.
3. Column Bracing Calculation
1) Internal forces in the column bracing of the rigid frame shall be calculated by considering the column row as a vertical cantilever truss supported on the column base foundations, subjected to the longitudinal wind load W acting on that column row (if cranes are present, the longitudinal crane braking force T shall also be included). For cross bracing, the compressive resistance of the bracing members may be neglected. The calculation schematic is shown in Figure 5-25. When multiple column bracings are provided in the same column row, the longitudinal force may be considered as uniformly distributed among the bracings.
2) For rigid bracing made of steel sections, local buckling is generally not a concern. Therefore, the design calculations for the bracing shall include: net section strength, overall stability, compliance with stiffness requirements, as well as the strength and stability of welds, bolts, and gusset plates at the bracing connection joints.