Vertical bracing systems
A variety of structural forms can be used to provide lateral stability. The principal systems are shear walls, lattice frames and rigid frames, but more sophisticated systems may be needed for very tall buildings.
Shear walls resist wind forces in bending by cantilever action and where they already exist, for instance to provide a fire protected service core, are an efficient method of carrying lateral loads. Lattice frames act as vertical steel trusses. Rigid jointed frames are less effective in providing lateral rigidity because of shear distortion in the vertical members. The British Standard BS 5950 sets a limit on lateral deflection of columns as height/300 but height/600 is a more reasonable figure for buildings where the external envelope consists of sensitive or brittle materials such as stone facings.
Rigid frames resist lateral loads by bending in the beams, columns and connections.
Rigid frames resist lateral forces through the stiffness provided by rigid joints between the horizontal floor components and vertical columns. The need to resist bending moments from wind loads increases the size of the column members and the complexity of the framing connections. For these reasons, rigid frames are only used when there is a particular functional reason for their use, such as the need to provide unobstructed interior space with total adaptability.
One possible exception to this general rule, is the facade frame with a combination of closely spaced external columns and deep spandrel facade beams. Such a system is usually used for very tall buildings where the facade frame forms a rigid tube.