Wind Load

[dik]

Any suggestions on how to apply a wind load to this. I was thinking about using the area of the top with a wind load using half the wind load value. It's not secured. Stability is provided by concrete blocks. It's going to be displayed and used by the public. The height is about 15'.

 

[jhnblgr]

My experience is with AASHTO signs and luminaries spec is what I would apply. Calculate the flat face areas and go from there. I guess you could use the shapes centroid and apply the moment arm to the base and figure the resisting moment required

 

[JStephen]

There's potentially a bunch of stuff vibrating up there, as well as the overall structure.
Why the "half the wind load value"?
At 15', if it blows over, that's a bit of hazard.
Can an athletic person jump up and grab a hoop?

 

[JAE]

What if a large sheet of plastic happens to blow onto the rings and create a sail? Or what if someone decides to hang a banner on it?

I'm always temped to way over-estimate the effective area of things like these.

 

[dik]

Why the "half the wind load value"?

because of the large amount of void.

 

[dik]

I'm always temped to way over-estimate the effective area of things like these.

Thanks JAE...

Can an athletic person jump up and grab a hoop?

Not likely... get a Darwin award. I think I will use the full wind load.

 

[dik]

There's potentially a bunch of stuff vibrating up there,

I think the 'structure' is pretty stiff; I don't think dynamics will be an issue.

 

[HTURKAK]

I was thinking about using the area of the top with a wind load using half the wind load value

Your approach reasonable . I would go with component force coefficients and use the effective area and apply solidity ratio.
Typical Cf could be 2.0 and this value will be divided to solidity ratio ε = As / Ag say if ε=0.33 Cf=2.0/0.33 =6.0 and this value would be applied to net area As.
I would suggest you to look Wind Loads for Petrochemical and Other Industrial Facilities-ASCE.

 

[dik]

Thanks HTURKAK... I've decided to go for the full wind value. The centroid of the load is close to the corner and unless I can get someone to measure it, my assumption will be a bit of a guess. If it's assembled I'll get them to balance it on an L3x3 to determine the centroid. I haven't done any sums on it yet and I don't know how much of a 'ballast' load to use. I was thinking of using an overturning factor of 2.5.

 

[SnTMan]

Curious. What does the public use it for?

 

[dik]

Curious. What does the public use it for?

Just decoration and a bench to sit on.

 

[SnTMan]

Ok, that explains the "bench" tag. LOL

 

[dik]

Closure on this... I've designed this with a reduced wind load based on an equivalent chain like fence resistance and I've used a 1/10 year return period wind load. I've designed the components for the full wind loading.

I've picked up another reference... ASCE 10... Design of Lattice Steel Transmission Structures, which delves into this in a bit of detail. I've reviewed this and as a guide it goes into great detail and yields results slightly more conservative to the approach that I've used.

I'm content with my approach.

 

[human909]

Closure on this... I've designed this with a reduced wind load based on an equivalent chain like fence resistance and I've used a 1/10 year return period wind load. I've designed the components for the full wind loading.

Thanks for providing closure. If I may I want to ask a question:
I'm curious what percentage was your final wind load? Eg; vs your initial approach of half the wind load value "using the area of the top with a wind load using half the wind load value"? (My gut feel here is to not go below half the wind load of the total area of the top.)


I design plenty of slender open steel structures. The code I use AS1170 has an Appendix on lattice framed structures which I'd imagine wouldn't differ greatly from ASCE. For the structures I uses which have approximately 70-75% porosity I usually end up with wind loads that are 60%-75% of a clad structure.

It all seems very conservative at first but when you start looking at how much the coefficient of drag varies between shapes it makes sense. My structures are full of 'rectangular' shapes with sharp corners (I-beams, angles, rectangular equipment etc.)


SOURCE: https://en.wikipedia.org/wiki/Drag_coefficient

 

[dik]

I used 0.5 as originally planned... the equivalent to a fairly 'dense' chainlink fence. I would suggest the porosity was approaching about 90%. The structure is low to the ground and is fairly sheltered. The steel components are not in a dense pattern. Also did not use 0.85 x DL for resistant weight. Actual weights and assumed centroidal distances have to be confirmed. Thanks for the added info...