Steel Structure Bracing System is the secondary structure, but it is an essential part. In the portal frame steel structure, the system has important functions, which is mainly used as: ensuring the stability of overall structure and individual components, transmitting horizontal forces to the foundation and auxiliary installation, etc. As for the building with complex layout, the bracing system is also with the advantage to adjust the structural rigidity, so that the structural stress is uniform and reasonable, and improved the integrity .
Setting principle of Bracing system:
In the portal frame steel structure, the bracing system can be divided into Roof horizontal bracing, Column Cross Bracing and Flange Bracing System.
The basic principles of Steel Structure Bracing System Setting :
- Clearly and reasonably transfer longitudinal loads to minimize the force transmission path;
- Ensure the stability of the structural system out of plane, providing lateral support points for the overall stability of the structure and components;
- Convenient installation of structure;
- Reach the necessary strength and stiffness requirements and have a reliable connection.
In the portal frame steel structure building, there are some regulations and requirements for different types of bracing.
(1) Roof Horizontal Bracing
Roof Horizontal Bracing and Column Cross Bracing are a whole, which together keep the structure stable, and the horizontal load is through roof bracing transmitted to the foundation via the inter-column bracing.
In order to ensure that the transmission path of the longitudinal load of the gable structural is short and fast, the lateral horizontal bracing of the roof should be set in the open space between the two ends of the building in order to directly transmit the gable load.If it cannot be set in the first opening room, it can be set in the second opening room.
When the structure is simple, symmetrical and the heights of the spans are the same, the roof horizontal bracing is relatively simple, it can be set only between the end openings.
In the building, when the column has different column spacing, or when the building has high and low span , longitudinal roof horizontal bracing should be set to improve the integrity of the structure and adjust the distribution of the lateral stiffness of the structure to reduce the rigid frame.
(2) Column Bracing
The column bracing is generally placed in the middle of the column. the horizontal tie rods of the column top should be designed as rigid tie rods to transfer the load on the horizontal bracing of the roof to the bracing between the columns. If the building is long, an additional bracing between the columns should be added. The bracing between the two columns is placed at 1/3 of the longitudinal direction. When the inter-column bracing cannot be set to the ideal position required by the structural design due to the requirements of the building, it can also be set off from the middle of the column. The inter-column bracing can be designed in a cross shape, or can be designed in a figure-eight shape, a gate shape, or even a rigid frame form.
It is best to use one type of column bracing in the building. It is not advisable to mix several types of column cross bracing. If it is due to functional requirements such as opening a door, window or other factors, rigid frame support or truss support can be used. When the support system must be mixed, the stiffness should be as uniform as possible. If the stiffness requirements are not reach, the longitudinal horizontal force of each support should be analyzed specifically to ensure the structure is stable and safe.
3) Flange Bracing
The Flange Bracing is unique to the solid-type portal frame light steel structure building. The flange bracing is disposed between the lower flange of the roof beam and the roof purlin or between the inner flange of the column and the wall girt. Supports the stability of the column and the beam. Flange Bracing is an auxiliary lever that does not become a system. The role of the stiffener of the rigid frame is to prevent the lateral beam from being laterally unstable when the lower wing is compressed.