Bracing05 May 2015
To manage seismic and wind loads in a pre-engineered steel building, many different forms of bracing are used. The most common is cross bracing but when building openings require clear, open bays, portal frames or wind columns are utilized.
Steel Building Bracing Types:
Cross bracing: This is the most common form of bracing in a pre-engineered steel building. Using solid steel rods, angles, or cables, each brace is fastened to the top and bottom of the main frame making an “X” between 2 rigid frames. Depending on the size and height of the building, and on the wind and seismic loads, the number of braced bays required will vary but at a minimum 1 bay per side is required.
Portal Frame: A portal frame is a secondary rigid frame positioned between two primary rigid frames in a bay. Portal frames are similar in construction to a rigid frame with two columns and a rafter. As this is an expensive bracing solution, portal frames are used when openings prevent cross bracing from being used.
Diaphragm Bracing – This form of steel building bracing does not meet the Canadian building code requirements and is not allowed in Canada. Using the roof and wall cladding, a skin, or diaphragm, is formed around the building to resist the forces of wind and seismic.
Weak Axis Bending – Steel buildings that require heavy loads on the columns typically use weak axis bending in order to increase the size of the base plates. These larger base plates help prevent the columns from moving under heavy stress.
Wind Column – If weak axis bending is not enough to secure the columns, wind columns may be used. A wind column is an additional vertical member used to help further secure the columns.
Flange Bracing – To counteract torsion, compression, shear, and lift forces, flange bracing, made up of structural angles connected between the rafters and purlins, is standard on all steel buildings. This bracing prevents the rafters from moving under a load.