Wind load on trellis 1

[tmoritz]

I am a mechanical engineer who needs some structrual engineering advice. I would like to construct a trellis to shade a portion of our future deck. The shading element of the trellis will be 2X6's set on edge. I may have up to 20 "joists" depending on the final dimensions of the trellis. My question is, do I calculate the wind pressure and multiply it by the total wind blown surface area? Is there some shadowing of 2X6's to the lee side of upwind "joists" which would reduce the total wind load? We live in Larimer County, Colorado and the county building code specifies a design wind velocity of 100mph so the wind loads will be quite substantial.

Tom Moritz
Mechanical Engineer

 

[aerohap]

I work for a company that builds a lot of steel trellis structures. If you apply the wind pressure as if the area were solid I'm sure you will find that your structure is already over designed. Usually we use a percentage of the pressure as a percentage of the open area per unit area.

 

[civilperson]

The shadowing or reduced pressure will come from identical shapes within 4 x vertical dimension behind the front element. Thus, for 2x6's on edge, a nominal 6" depth will be pushed by the wind every 24". If the spacing is equal to 24" or greater, each element will receive the full wind pressure.

 

[tmoritz]

Thanks civilperson. This is the info I was looking for. It'll reduce both the moments and the footing reaction forces I have to design for.

Tom Moritz
Mechanical Engineer

 

[miecz]

I have a copy of an obsolete british loading standard for the design of buildings that has a provision for "Shielding effect". The sheilding factor varies by the "spacing ratio", the ratio of the spacing to the depth of the member. For a spacing ratio of 2, the shielding factor is 0.43. a spacing ratio of 3, the shielding factor is 0.48.