NCC 2022 Vol 1 S8C2: Precast panel height to thickness ratio

[will.sce]

I'm wondering what people's interpretations of this clause in the NCC are, regarding precast panels under "performance of external walls under fire".

The clause states:

"This Specification applies to buildings having a rise in storeys of not more than 2 with concrete external walls that could
collapse as complete panels (e.g. tilt-up and precast concrete) which—
(a) consist of either single or multiple panels attached by steel connections to lateral supporting members; and
(b) depend on those connections to resist outward movement of the panels relative to the supporting members;
and
(c) have height to thickness ratio not greater than 50."

I've spoken to a number of engineers and the interpretation of "height to thickness ratio" differs. Should height be treated as effective height (according to AS3600), or true overall height?
For example, can a 180 thick panel only be an absolute maximum of 9m tall? Or is it suitable for it to be supported by a wall tie at 9m, with connections designed appropriately under fire conditions?

Thanks in advance

 

[mrlm]

I haven't had a lot of experience dealing with this situation, however, I would find it unlikely that it should be treated as effective height and should be true height.




The attached paper makes reference to a couple of situations and recommendations on slenderness limits. Similar to what the paper shows, unless you can demonstrate that your selected combination of steel support structure and tilt-up panel will not collapse outwards, I would suggest sticking to the limits in the NCC.