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Diagonal bracing to stabilise roof planes

Diagonal bracing is required to address top chord distortion. It is used in other parts of the roof as well, for example, the bottom chords and webs. Bracing is often provided by a steelbrace. A steelbrace is made from metal strapping and has a slight bend along the centre line. A typical specification for steelbrace is shown below.

Diagram of a specification for an L-shaped steelbrace with each arm 20 deep. The angle between the arms is 120 degrees. Countersunk holes are at a horizontal distance apart of 16.

Diagonal steelbraces that cross over the top chords act as tension ties. If the ties are only fixed at the ends, the mid regions of the top chords can still move sideways. If the steelbrace is fixed to every element it crosses, the forces arising from wind or lateral buckling can be transferred to the supporting structure. Consequently, the whole assembly can be kept square.

The steelbrace must also be attached to elements such as walls that transfer loads to the structure.

Diagram of a roof with diagonal steelbraces that cross over the top chords, but which are tied only at the ends. The chords have buckled.
Ties are only fixed at the ends
Diagram of a roof with diagonal steelbraces that cross over the top chords and are fixed to every element they cross. The assembly has remained square.
Steelbrace is fixed to every
element it crosses