Wind Load on Trellis 1

[XR250]

I have a 30 ft. x 30 ft. trellis with perimeter HSS beams and two intermediate HSS or I-beams to break the rafters into 10 ft. spans. For wind perp. to the rafters, does anyone have any info on the wind shading from rafter to rafter? I found an old post from 2006 that states anything within 4d spacing is considered shaded. Not references were cited, however.

Thanks.

 

[AaronMcD]

Following.

Also, what about uplift on thin rafters? I feel like it would be something more than on the summed area and less than the full area, but couldn't find any references.

http://www.hellodwell.design

 

[JoshH726]

You can try AISC’s paper on wind loads on pipe racks? It’s an engineering journal article so it’s free with a membership.

https://www.aisc.org/products/engin...-of-structural-steel-pipe-racks/#.XVthxSQpCEc

 

[GC_Hopi]

Try searching the forum for wind loads on open structures. This question has asked before.

 

[XR250]

Thanks' y'all!

Not finding anything too encouraging in the archives. The responses range from wind on first and last rafter to using a 30% shading factor on each member.
Let's face it, if trellis's actually had that much effective wind area, they would be failing all over the place. I have yet to see this happen.
If I do 30% shading, the wind load is pretty un-manageable as this thing is huge.

Anyone else got something?

 

[dold]

I recall a while back someone mentioning how eurocode addressed this. Essentially they consider the wind load applied at a 10degree inclination and the resulting load on each rafter is whatever the projected area on each member is. Seems a bit more manageable than 30% rule.

 

[dauwerda]

ASCE's "Wind Loads for Petrochemical and other Industrial Facilities" addresses this in the case of wind loading on pipe racks, where you have multiple pipes side by side with a transverse wind. It is essentially what dold alluded to above where the wind can strike at an angle from horizontal. ASCE uses a slope of 1 to 10 (5.7 degrees), this is accounted for by using the largest pipe diameter plus 10% of the pipe rack width when calculating the tributary area. See snippet below from ASCE for further explanation/clarification.

 

[XR250]

Thanks!