Wind codes and unrealistic velocities/pressures

[pwht1]

Hello,

I was told to design some purlins by a senior engineer that must be Stramit Z250-15 at 1500 centres. These things are spanning 11m and after a few checks I find they fail under the wind pressure from AS1170.2(the Australian wind code), no big surprise. I go back to the engineer and report what he needs to get it to work and he rejects it. He proceeds to tell me that the wind code is unrealistic and I should "reverse-engineer" the purlins. So here's the question, what wind code does give realistic pressures and what's you view on AS1170.2 (if you're familiar with that code)?

Thanks,
Paul

 

[apsix]

By AS/NZS1170.0 Appendix C, Amendment A2, the correct load APE when checking deflection is now 1/25 (it used to be 1/20). This makes no practical difference for Region A.

The use of V1000 implies that you are designing a building designed to contain a large no. of people (BCA Table B1.2), it's not what I would use for an office.

None of that helps your deflection issue, the local pressure factor can be a killer for large buildings.
Note that the factor should only be applied to external pressures.

 

[pwht1]

Appendix C is an "informative" part of the code, compliance is not necessary. A 1/25 velocity doesn't seem to be a significant increase (0.3m/s), why would they bother?

It's 120m long by 70m wide and will later be converted to a covered carpark. So quite a few people can fit in there...

Thanks but I'm aware of all that, do you know anything about the permeability for metal clad roofs csd referred to?

 

[rscassar]

See thread thread744-237727 regarding whether a 1/25 or 1/20 should be used for serviceability design. I personally use a 25yr recurrence (I'ma cautious cat). Haven't looked at region A but in region B this results in a 10% increase in load.

If you are going to call up an increase lap length make sure you review this when shop drawings are submitted. I have a feeling this would be something a steel detailer would miss when producing shop drawings.

 

[rowingengineer]

The permeability has to do with sheeting rib openings at slab level, windows, opening above roller doors and ridge vents. The commentary gives some guidance here with sheds and industrial warehouses at about 0.5% and offices at about 0.01% or something along those lines. You can work it out, which is what I suggest you do to get a feel for the value.

This is used to reduce your internal pressure for dominate opening. Be careful however as roller doors done have a good recorded for staining wind pressure.


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