The longitudinal structural rigidity of portal steel frame structure is relatively weak in the length direction, so it is necessary to set up bracings along the longitudinal direction to ensure its longitudinal rigidity and longitudinal stability. The main function of the bracing system is to transfer the wind, crane load and earthquake load imposed on the longitudinal structure from its point of action to the main load-bearing structure, and finally to the foundation. At the same time, the horizontal frame is connected into a geometrically invariable system to ensure the structure can bear the load.
Upper horizontal bracing should be set on the top surface of the beam, and inter-column bracings shall be set between the columns. These bracings should be set in the same room. Because the resultant force of rind bracing force to the roof beam is finally balanced by the bracing system, the support plane is required to be as close as possible to the plane where the rust is located, which could avoid eccentricity of the entire roof longitudinal force transmission system. For the crossed scissor brace, if the rod is selected from the round steel, it can be achieved by drilling the web near the upper flange or welding the connecting plate on the upper flange directly as the connection point. If angle steel is used, the connecting plate can still be welded to the upper flange.
The bracing system of the light portal steel frame structure includes roof horizontal bracing and inter-column bracing. According to the working mechanism, it could be divided into flexible bracing and rigid bracing. According to the structure, the inter-column bracing is divided into oblique cross-bracing and rigid-connected column bracing. Flexible bracing components are galvanized steel wire ropes, round steel, strip steel or angle steel. Due to the relatively large length of the components, they can hardly be compressed. Under the action of a longitudinal load in one direction, the component will be out of work when the other one is pulled. But a square tube or a round tube can withstand tension and pressure as a rigid bracing part. The structure of the cross brace contains the advantages of simple, direct force transmission, fewer materials, and greater rigidity. It is a standard bracing system for roofs, side walls and gables in light steel structure buildings. Due to the requirements of building function and appearance, cross bracings cannot be set in some bays, and portal bracings can be set at this time. This type of bracing can be longitudinally fixed in the space between two side pillars or between the inner pillars of a multi-span structure. Column support with a column foot fixed to the foundation around the weak axis is mostly used to shield the building structures. For example, the most used is steel carport structure, which requires the wall to be completely open for cars to enter and exit. These buildings are usually very long, with low eaves and many bays.