WorkSafe inspectors have observed construction sites on which the braces supporting concrete panels were installed skewed, i.e. not in a plane perpendicular (at 90 degrees) to the plane of the panel, risking collapse of the panel and putting workers at risk of serious injury.
Skewed braces are weaker than those installed in a plane perpendicular to that of the panel (when viewed in plan). This is because they have less capacity to bear load, which can affect the stability of the precast panel.
Recommended control measures
Brace manufacturer and supplier load charts specify that braces must:
- be inclined no less than 40 degrees and no more than 60 degrees to the horizontal
- be installed in a plane perpendicular to that of the panel (when viewed in plan).
WorkSafe will typically not accept braces skewed more than five degrees on either side of the plane perpendicular to the plane of the panel.
Where braces cannot comply with these two conditions, the design and installation must consider factors such as induced lateral or torsional forces. The proposed brace design must then:
- be verified by the erection design engineer
- clearly specify the limit of the skew, and
- be shown clearly on shop drawings.
The above diagram is a plan view that shows the limit of skew recommended for braces when supporting precast concrete panels.
WorkSafe accepts that plus or minus 5 degrees is effectively perpendicular. Braces should therefore be installed in a plane perpendicular (at 90 degrees) to the plane of the panel (plus or minus 5 degrees) as per manufacturer and supplier specifications.
WorkSafe inspectors will accept braces at greater than 5 degrees of skew provided the conditions listed under the three bullet points above have been met.
Note: This guidance is based on an archived WorkSafe Victoria safety alert, originally published September 2009.
- AS 3850:2015 Prefabricated concrete elements
- Precast and tilt-up concrete for buildings: industry standard