Revised internal pressure calculation in AS/NZS 1170.2:2021? 1

[QLD_eng]

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 opening, for large openings]

The revised 2021 version defines the internal pressure coefficient as the external pressure coefficient multiplied by he local pressure and area reduction coefficient. [i.e. Cp,i = Ka.Kl.Cp,e at the opening, for large openings]

My interpretation of the effect of this, is that for most structures in region C and D (and possibly some in other regions) the internal pressure go up very significantly. The old 'standard' internal pressure for region C and D was +0.7,-0.65 (which is reflected in AS4055 as the default internal pressures). But now these pressures would conceivably be [+0.7*1.5,-0.65*2]=+1.05,-1.3. (or even higher depending on the geometry)

So my question is, am I reading this correctly, and internal pressures are generally going up? And if so, why does the revised version of AS4055:2021 keep Cp,i = +0.7,-0.65 instead of +1.05,-1.3?

 

[blihpandgeorge]

see from around 24min onwards, [URL unfurl="true"]https://www.youtube.com/watch?v=DfJx830H9JA[/url]

 

[QLD_eng]

Thanks. Thats a great video.

 

[m_struct]

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

Also, any chance we can see that video again?

 

[rowingengineer]

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

https://youtu.be/6gnRaAN9SOY