Aerodynamic Shape Factor in AS 1170.2 from (ISO4354)

[waves]

Can anyone help me to understand the application of the Aerodynamic Shape Factor (Cfig) as used in calculation of design wind actions on a structure. I am looking at a purlin design for a monoslope free roof (carport)structure and am having trouble interpreting Table D4(A) as depicted in AS/NZS 1170.2:2002. Is it correct to sum the effects of windward and leeward values in calculating the net pressure coefficient for the roof ? ie Cpw + Cpl = Cpn thus Cfig = Cpn Ka Kl

 

[austim]

HI, waves. Whatever you do, do not simply rely on what follows without confirming it for yourself from the standard.

Having just retired within months of publication of the new loading code, I chose not to buy a copy of the dinkum document. What follows is based in my reading of draft 99419. I would be reasonably confident that I am close to the right track with my thoughts, however.

In the draft, clause D 3.1 describes what Cpw and Cpl are all about. (Hopefully the code committee did not depart from the draft on such a basic matter). That says quite clearly that cpw is to be applied to calculate the local nett pressure on the windward half of the roof, and cpl on the leeward half.

Hence cpw and cpl do not apply to opposite faces of the roof, (which would have to be the case if you had to add cpw+cpl to any area) but only to different areas.

So yes, you add the effects of cpw on one half to the effect of cpl on the other half, but you never have to add cpw+cpl to get a nett pressure coefficient - they are both nett coefficients already.

 

[waves]

Thanks austim.
I also picked the brains of our senior structural guru this afternoon. His explanation was basically the same, so I am feeling slightly more confident with the application of the Aerodynamic Shape Factor now.

If you would like a copy of the final code post your email and I can send through a .pdf.

 

[austim]

waves,

Thankyou for your response. I am glad to have been of some help.

As for your offer to e-mail a copy of the final code - thanks, but no thanks. I am sure that would constitute a serious breach of Standards Aus copyright, but in addition I am now really truly retired, and have no need for the real code. If I had, I would have bought it by now.

(I now have 'run-off cover' on my Professional Indemnity policy, which will provide protection in the future for any claim that might arise in the future for work that I have done in past years, with no further premiums payable. A principal condition of that extension of my cover is that I "am not working as an engineer" at the time of any such claim&quot.