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Bracing in steel structure

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Bracing is important part of steel structures. Bracing is added to increase the structure strength and increase structure stability when subjected to lateral loads such as wind load, earthquake load and others. In steel structures, columns and beams resist different loads such as axial loads, shear load, flexural stresses, etc. But without sufficient bracing structure will not be stable against lateral load and deformation can be large and beyond the acceptable. Therefore, the bracing is added to  significantly reduce the structure deformation due to external loads. 



The main purpose of bracing is to ensure the structure lateral stability. Without bracing, structure will excessively sway. The structure significant deformation due to sway can result in damaging several elements of the structure such as connection, walls, cladding and others. 

Bracing elements usually fabricated from steel sections such as angles, channels, rod, hollow sections or I sections. The bracing is usually placed between columns and beams in different arrangements. The most common type of bracing is the diagonal bracing (x),  V-bracing, inverted V-bracing, and K-bracing. Each bracing type has a different behavior, the bracing type is selected by the designer according to design requirements, architecture limitations and loading conditions. 

Diagonal bracing is the most common type of bracing, in this type of bracing, two bracing elements cross each other forming an X, the bracing elements will cross from one column to other. In this type of bracing, one element will work in tension while the other will be in compression depending on the direction of the lateral load. This type of bracing provide a high stiffness and it is commonly used in industrial building, warehouses, multistory steel structures. 

V bracing also common. In this type of bracing the bracing elements will be similar to V and it will meet at one point at the beam. This will be useful when there is a need to opening in the frame such as door or windows. 

Bracing are divided into vertical bracing and horizontal bracing. Vertical bracing are placed in the vetical direction between the columns to resist lateral loads and prevent excessive deformation. While horizontal bracing used between beams to distribute the lateral loads between frame and provide diaphragm action. 

Load transfer path is very critical, when the wind or earthquake act on the a building, the stresses is transfered from cladding or floor system to beams, then bracing, then column and finally to foundation. The bracing system should provide a clear and continuous path from the top of structure until the foundation. 

Bracing reduce the effective length for columns (compression members), which means that the column resistant to buckling will increase. In steel structure, buckling is considered as the main failure mode especially for slender compression members. The column bracing reduce the unbraced or free length which increase the member strength and stability. 

Connection in bracing is critical, the bracing element should be appropriately connected with the columns and beams. Connections can be bolted or welded types. Weak connections can reduce the effectiveness of the bracing and may result in structural failure. Therefore, connection should be sufficiently strong to safely transfer the tension and compression stresses. 

During the design stage the Engineer should consider, strength, stiffness, stability and ductility of the bracing system. Ductility is very important to allow the structure to absorb the energy generated during earthquake without sudden failure. Some bracing system are designed to yield and deformed in controled manner to protect the main structural frame. 



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