Wind load on large potted plants/trees.

[azcats]

We've got a project where 'someone' is attempting to do 'something' unconventional and I need to figure out how to account for wind loads of large potted plants. Code is ASCE 7-05. Plants are unknown at this time, but we should have something on that soon. Are there any published data (or best practical guesses by members here) for what Cf and Af I should use for design. Conservatively I could go with solid walls/signs, but that seems like it might be punitive. Or it might not...some plants are pretty dense.

Another worry is how do I limit or design for growth? I can put limits and maximums on the drawings, but the plants won't care. Are there data on how tall plant X will grow in pot of size Y?

Input appreciated. Feel free to ask questions.

 

[msquared48]

I would contact a horticulturist for how big a particular species of plant is likely to grow in a pot of a particular size.

As a side note, make sure the plants are not allowed to be replanted to bigger pots - they frequently are to prevent them from becoming rootbound.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[JAE]

Depending on the plants and their location on the building I would use signs, parapets or similar to mimic the wind loads. Wind doesn't care whether the obstruction is green or concrete gray.

 

[Ron]

Agree with Mike and JAE....I've done similar on roof-mounted planters. Best you can do is make sure you research the plants, how big they will get, and how the pots/planters are attached (or not) to the structure. If you are in a high wind area, these become windborne debris.

 

[msquared48]

An arborist would help too.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[JAE]

I'm not sure how you would apply ASCE 7 to say a potted tree - if the tree would theoretically break over at something less than the 90 mph code wind speed...that would be another question to ponder. For potted plants not connected to the building you also have the situation where they could tip over.

 

[BigInch]

I hate to think that a design is being controlled by potted plants. Does something need a re-think here?

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[Ron]

BigInch....clients have some peculiar requirements sometimes. I once did a very large aluminum canopy over a parking area (whole lot was covered by canopy), that had planters on top that could be seen from the building above. These were long span members in a 120mph wind area with heavy planters sitting on top. Literally the tail was wagging the dog in this instance.

 

[BigInch]

No doubt. He that holds the gold maketh the rules.
Let me rephrase the question.
I guess the planters would tend to hold the roof down in the high winds.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[msquared48]

That depends on whether or not it was big enough to stay there...

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[OHIOMatt]

If you know the size of the pot, then you likely have all the information you need. Assuming that the pots are resting, unrestrained, then you can calculate the moment required for overturning as well as determine the amount of shear required for sliding. The plant can only impart force to the pot and supporting stucture until the pot overturns or slides.

 

[azcats]

Thanks for the input all.

The information I have has evolved over the last several days.

First, this is a temporary display with a maximum 60 day life. Therefore (theoretically) I will have control over the size of the plants.

Second, the plants will be anchored to my structure. They are in a place that they can't be allowed to tip and fall.

So I guess my questions have changed somewhat. I'll likely use the projected area with a sign/parapet for design. However, for a short term load, would anyone recommend (allow) using lower wind speed or reduced safety factor? It's a situation where I'm trying to balance a short term additional dead load where wind loads (especially at a 50 year event) will contribute very significantly to design loads. However, I also need to be balance all this with the possible scenario that someone would like to make these permanent. Man...I didn't like writing that because I then lose control of my plant size too.... Perhaps I've answered my own question.

 

[rb1957]

a temporary display clearly resolves many questions (growth, chance of high wind, ...)

not sure how you can anchor the plants to your structure. sure you can restrain the pot, but are you putting a collar around the stem of the plant and anchoring that to the supporting structure ? then are you looking at the stem breaking at the collar ? getting an allowable moment on the stem based on diameter and tensile strength, then relating this moment to wind load and a wing speed (or of course the other way 'rounf ... wind speed, airload, moment, stress)