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Purlin Outwards Capacity vs "No Cladding" capacity?

Purlin Outwards Capacity vs "No Cladding" capacity?

Purlin Outwards Capacity vs "No Cladding" capacity?

(OP)
Purlin tables typically list two capacities. 1. inwards capacity (where cladding restrains the critical flange) and 2. outwards capacity, where there the cladding is on the non-critical flange.

Does outwards capacity depend upon cladding on the non-critical flange? Presumably the cladding provides *some* rotational and lateral stiffness to the purlin, I'm just not sure whether the tables are including it or not.



RE: Purlin Outwards Capacity vs "No Cladding" capacity?

Tomfh,
I believe some utilize FE analysis to validate tabulated values.
In a more simplistic sense, I would consider the cladding to not provide torsional resistance, only translational, but it acts as a "stabilizing" load (loads away from shear centre in outwards mode, assuming it is the cladding applying the load). Together with bridging, the cladding will provide a couple and thus torsional restraint (bit of a lean on effect I suspect, if no direct load path provided), hence increased capacity for increased number of bridging.

Toby

RE: Purlin Outwards Capacity vs "No Cladding" capacity?

(OP)
Thanks for the comment. I tend to agree it will help stabilise the Purlin. What I'm really wondering is have the purlin msnifacturers included that effect in their "outward capacity" tables?

Put more simply - is "outwards capacity" ok to use if there's no cladding at all?


For simplicity let's assume 0 bridging

RE: Purlin Outwards Capacity vs "No Cladding" capacity?

How is the purlin been loaded if not via the cladding? Compression?

RE: Purlin Outwards Capacity vs "No Cladding" capacity?

(OP)
Heavy Beams stacked perpendicular on top of the purlins.

RE: Purlin Outwards Capacity vs "No Cladding" capacity?

Since claddings can take a variety of forms, from sheets, to sheathing, to brick, to stucco,.....and the stiffness of such claddings will also vary significantly, unless there is a table available for each cladding or group of claddings I would consider that no cladding influence is included.

RE: Purlin Outwards Capacity vs "No Cladding" capacity?

(OP)
Ron, so in your opinion it would be safe to load unclad purlins based on the "outward loading" tables?

RE: Purlin Outwards Capacity vs "No Cladding" capacity?

"What I'm really wondering is have the purlin msnifacturers included that effect in their "outward capacity" tables"

Have you called the manufacturer?

RE: Purlin Outwards Capacity vs "No Cladding" capacity?

Tomfh..check both and be conservative, but "yes".

RE: Purlin Outwards Capacity vs "No Cladding" capacity?

The AISI Specs have procedures on how to design a zee or cee for uplift loads when there are through-fastened cladding panels attached to the outside (tension) flange. For example, for an 8" deep simple span zee there is a reduction factor of 0.65. More than likely the purlin manufacturer used these reduction coefficients to come up with the values in their table.

RE: Purlin Outwards Capacity vs "No Cladding" capacity?

(OP)
J19

That AISI factor does sound similar to the tables in the stramit and lysaght purlin tables I'm familiar with. The outwards load is often around 60% of the inward.

So in the case of AISI specs, my question is - would it be appropriate to use that factor if there is no cladding, or should a lower factor be used?

RE: Purlin Outwards Capacity vs "No Cladding" capacity?

No, you shouldn't use those factors if you don't have cladding. The Spec also has a list of criteria that the cladding has to meet in order to be able to use the factors. If you don't have cladding for your situation I assume you will have some type of bridging between the purlins?

RE: Purlin Outwards Capacity vs "No Cladding" capacity?

(OP)
Thank you all for the pointers.

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