Lateral restraint for bottom chords

Bottom chords also need to be braced against lateral buckling and distortion. The treatment of the ceiling and its type of attachment to the bottom chords affect the need for restraint.

Ceilings fixed directly to the bottom chord require minimal bottom chord ties, for example, ties not exceeding 4,000 mm apart. Ceiling battens nailed or screwed to trusses provide lateral restraint similar to roof battens so no additional restraint is needed.

Suspended ceilings or battens that do not provide lateral restraint need bottom ties, eg clip on battens. These must comply with an approved specification.

Ties must be attached to building elements capable of taking bracing loads. Steelbraces should be used to prevent ceiling plane distortion.

Two diagrams showing plan views of bottom chords of a roof. Length and width are marked as 'Span' and 'Span/2'. Steelbraces run diagonally across each half of the roof and bottom chord ties are shown.