Braced & un-braced frames

Braced frames use trussing to resist sideways forces on buildings. Trussing, or triangulation, is formed by inserting diagonal structural members into rectangular areas of a structural frame. It helps stabilize the frame against sideways forces from earthquakes and strong winds.In a braced frame, bracing is usually provided in every storey of the building.Braced Frames - Single DiagonalsIf a single diagonal, or brace, is used, it must be able to resist tension (stretching) and compression (squashing) caused by sideways forces in both directions on a frames.

Cross BracingIf two diagonals are used, in the form of cross-bracing, they only need to resisttension. This is because one brace is in tension for the sideways force in one direction on the frame, while the other brace is in tension when the force is reversed. Steel cables can be used for cross-bracing, as they can be stretched, but not squashed.

The frames without bracing is called un-bracedThe frame with bracingUn-braced when Vsd/Vcr 0.1- Braced when Vsd/Vcr 0.1- Vsd is the design value of total vertical load applied to structure.Vcr is the elastic critical vertical load produce sway instability of structure, Must allow for 2nd order analysis.

second order analysis include both the sway and member deflection effect by modifying the member stiffness term, iteration and convergence procedures are required.