Wind uplift on bar grating

[jmurph36]

Hello all,

My company designs a lot of structures for the mining and aggregate industry. Typically, we use 19W4 bar grating for the floors on the towers we design. I have struggled a lot with vertical effects of wind on these structures. Some in our office have the opinion that we should include vertical loads as if the bar grating was a flat roof on the structure. However, I have the opinion that, even if there is vertical aerodynamic forces, they would be reduced because of the porosity of the bar grating. I have read another thread here that alludes to that, however, I can't find any recognized literature or guidance that gives any suggest values to reduce this load. Does anyone have any experience/insight into this?

Thanks!

 

[dik]

I'll see if I can dig it up... but, there is a publication that is used by chainlink fence designers for amount of opening and effect on wind load.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik

 

[dauwerda]

Roof uplift is caused by differential pressures between the external surface of the roof and the internal surface of the roof. If this is an open structure (no walls) I really don't see this being an issue as you would have similar air movement (and pressure) both above and below the bar grating.

 

[WARose]

I have struggled a lot with vertical effects of wind on these structures. Some in our office have the opinion that we should include vertical loads as if the bar grating was a flat roof on the structure. However, I have the opinion that, even if there is vertical aerodynamic forces, they would be reduced because of the porosity of the bar grating.

In 'Wind Loads for Petrochemical and Other Industrial Facilities', p.78, it says this:

"No research related to open grating floors has been published. There is no evidence that open grating floors will significantly affect the wind forces on the structure."

That's in the section on open structures.

 

[Mike Mike]

I think a reasonable way to calculate the wind load on your grate is per ASCE 7-10 29.5.1, considering your grate to be a rooftop "lattice framework". The vertical force on the grate is qh x GCr x Ar. Yes, load is reduced by the porosity, inherent in Ar. I skimmed through the ASCE Guide to the Wind Load Provisions publication and it did not appear to have any additional info. The ASCE 7-10 commentary suggests Hosoya et al. 2001 and Kopp 2008 for further reading.