Steel purlin calculator

[ed110220]

Hi all,

does anyone know of span and load tables for steel L-section purlins?

I'm considering replacing my roof covering and need to know whether the purlins could safely take the weight of the new covering.

The purlins span 3300 mm between trusses at 1300 mm centres. They are 64 x 51 x 6 mm in section with the long side at right angles to the roof covering. The roof has a pitch of 22 degrees.

The new covering would have a mass of 16 kg/m^3 (not including any new rafters).

 

[noseall]

Is this some kind of corrugated sheet material roof on a pre-fab building?

If so, how does the existing material weight compare the the proposed?

 

[ed110220]

Is this some kind of corrugated sheet material roof on a pre-fab building?

If so, how does the existing material weight compare the the proposed?

Yes, sort of, it's a corrugated asbestos cement covering on a steel framed BISF house. Looking it up, asbestos cement has a density of 1,550 to 1,950 kg/m^3.

I'm not sure of the exact thickness of the sheets, but assuming 1750 kg/m^3 and a thickness of 5mm that would be 8.75kg/m^2, not accounting for the extra weight of overlapping and the corrugations (ie calculating it as one flat sheet).

Like this:

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[ed110220]

Proposal is to add an 18 mm OSB3 or ply deck with a standing seam metal covering such as Euroclad Vieo or Tata Colorcoat, if the weight is not too much.

As it's an unusual structure for a domestic roof there's little information - it's more like a warehouse or barn roof but on a smaller scale.

Edit: some sources give weights of 16 kg/m^2 or more for asbestos cement sheeting.