BCGBC4010A Apply structural principles to residential low-rise constructions

Structural principles - Structural members

Wind bracing

Theory of triangulation
Structure with no bracing member
This structure has pinned joints but has no bracing.
A diagram of a structure with no bracing is shown with force applied to the left side of the structure. The structure will bend to the right due to the force.
Structure with a bracing member in tension (tie)
Triangles create stability when added to a structure. Diagonal bracing in the form of a tie has been inserted into this structure. This bracing member is in tension. Note that all the joints are still pinned, so they do not need to resist bending moments.
A diagram of a structure with a tie is shown. The tie spans diagonally from the bottom left hand corner to the top right hand corner. When force is applied to the structure from the left the tie pushes the force from the middle back to the corners. The structure remains in the original position. 
Structure with a bracing member in compression (strut)
In this structure the brace is a strut as it is in compression.
A diagram of a structure with a strut is shown. The strut spans diagonally from the bottom left hand corner to the top right hand corner. When force is applied to the structure from the right the force travels to the middle of the strut. The structure remains in the original position.
Conclusion
It may be necessary to use a sectional shape that works well under both tension and compression.

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