Deflection is the amount of bend or sag over the span.
The Australian Standards® limits deflection.
What is Allowed?
Span/300 as per AS/NZS 1170.0 or
10 mm over 3 meters.
Why is it important?
Bigger spans require stronger steel.
It is Illegal to Sell or Certify a Shed
in Australia that is not deflection compliant.
Why are centers important?
Centers means the distance between Top Hats.
Bigger centers require stronger steel.
A Top Hat's strength dictates its maximum centers.
For The Mathematically Curious
These formulas are not closely guarded trade secrets.
They are basic engineering calculations.
Maximum Legal Deflection
Span / 300
Actual Deflection
(5/384) x P x Span4 / (E x Ix x 106)
Maximum Legal Centers
(Maximum Legal Deflection x (E x Ix x 106)) /
((5/384) x Governing Roof Pressure x Span4)
About the Top Hat Span Test™
This Test and its results are limited to Bluescope® Hi-Tensile Australian Steel.
Deflection & centers cannot be calculated without the certified structural properties and span tables for the steel. Bluescope® publishes this information.
This calculator is a guide only and does not apply to roof only structures.
Engineering is site specific, so take your quote, design specifications and site address to an Independent Registered Structural Engineer.
