Revised internal pressure calculation in AS/NZS 1170.2:2021 Part 2

[Tomfh]

This is a follow up from the following thread:

Revised internal pressure calculation in AS/NZS 1170.2:2021? - AS/NZS (au/nz) Code Issues

In the recently revised wind code, there is a change to the way internal pressures are calculated for structures with dominant openings. The 2011 version defined the internal pressure coefficient as the external pressure coefficient at the location of the opening [i.e. Cp,i = Cp,e at the...

www.eng-tips.com

In it, someone asked:

For the Kl part, is it still only referring to cladding, cladding fixings, elements that supports cladding, and this fixing?

to which @rowingengineer replied:

For KL internal pressure it applies to all parts of the building. This has been clarified by the code committee.

Can anyone confirm/clarify this? Are local pressures at the locations of openings now applied to all internal surfaces simultaneously, including loading of primary framing members?

 

[sdz]

5.4.4 Local pressure factor (Kℓ) for cladding
The local pressure factor (Kℓ) shall be taken as 1.0 in all cases except when determining the wind
actions applied to cladding, their fixings, the members that directly support the cladding, and the
immediate fixings of these members.

1.4.6 cladding
material that forms the external surface over the framing of a building or structure

Kℓ is applied only to external pressure on cladding and is combined with the appropriate internal pressure.

Hence pnett = qz(Kℓ Cpe - Cpi)

 

[Tomfh]

Table 5.1B says Kl applies to internal pressures when there are external openings greater than 0.5% which are located in the corresponding external local pressure zone.

The reply I quoted above suggests this applies internally not just to cladding and its supports (which is already quite drastic), but to the whole building, presumably meaning the structure itself. So I'm querying if I've understood this correctly, does it also apply to the main structural members?

 

[sdz]

Table 5.1B says Kl applies to internal pressures when there are external openings greater than 0.5% which are located in the corresponding external local pressure zone.

The reply I quoted above suggests this applies internally not just to cladding and its supports (which is already quite drastic), but to the whole building, presumably meaning the structure itself. So I'm querying if I've understood this correctly, does it also apply to the main structural members?

You're right. However;
For nominally sealed buildings you'll be using Table 5.1A. Table 5.1B only applies for dominant openings.

When there is a dominant opening;
When Kl affects internal pressure it affects entire surfaces so it is no longer a local pressure on those internal surfaces.
When the area of the opening A>a^2, Kl =1
When A>10m^2, Ka<1.0

If say, you're looking at an industrial building with truck size opening, then you will most likely have Kl =1 and Ka<1.0.

For internal walls the extreme combination of pressures on either side would only need to be used for structural walls.

 

[Tomfh]

Table 5.1B only applies for dominant openings.

That's what this thread (and the thread it follows on from) refers to.

When Kl affects internal pressure it affects entire surfaces so it is no longer a local pressure on those internal surfaces.

That's not what the table appears to say. Say you have a small (0.5%) opening at a Kl=1.5, or 2, or 3 external local pressure zone, then by the table this local factor applies to all internal surfaces. If we're reading this wrongly, it would be good to know.

 

[rowingengineer]

Tomfh,

Do you have this book? I thought they had an example in it, maybe not but if my memory serves me it did.

Wind Loading Handbook For Australia & New Zealand – Background To AS/NZS 1170.2 Wind Actions (2021) (electronic version) – The Australasian Wind Engineering Society

awes.org

 

[Tomfh]

Do you have this book? I thought they had an example in it, maybe not but if my memory serves me it did.

No. I’ll check it out.

In your reference to “clarified by the committee”, what specifically were they clarifying, and where did they clarify it?