How much concrete is required to anchor down a gazebo? [closed]

Question

My wife and I bought a put-it-together-yourself gazebo from a hardware/outdoor type store (think Home Depot or Big Lots type of place). It is rectangular gazebo (10'(w) x 12'(l) x 10'(h)) with a cloth roof and sides. The box of parts says it all weighs about 130 lbs (60 kg).

I'm trying to figure out how to anchor this down. The instruction manual is one of those look-at-the-picture-and-guess-how-it-goes-together deals. The only thing it shows is "put stake in ground". Each corner has a small base plate with holes for 4 stakes. Each stake is an 6-ish inch long L-shaped stake with "threads" on them (they look like threads on a screw except they are wide, something like 1/8 of an inch or so).

Being an engineer (but not the kind that deals with structures or anything) I'm trying to figure out if staking into the dirt is sufficient or if I need something like concrete to anchor this down. I'm also trying to not over-engineer this. My biggest concern it that if I don't anchor this down sufficiently, I'll have a gazebo trying to make a forceful entry into my kitchen one day.

So my question has a couple (related) parts:

1. Is anchoring into the dirt sufficient?
2. If not, would concrete be a good way to anchor it? If so, how much per foot do I need to use?

My initial thought was to put one to two 50 lb bags of concrete mix in a hole at each corner. I've never done concrete by myself before (aside from digging holes for it with my dad when I was younger) so this is all somewhat new territory for me.

Answer 1

First, I should disclose that I voted to close as opinion-based. The answer depends almost entirely on your tolerance for risk and your effort/cost budget. Anyway, here are my thoughts.

1. A structure of that lightweight design doesn't call for concrete. It'll be torn apart by high wind before it'll pull out good soil anchors.

2. The anchors that came with the kit don't sound adequate. I'd purchase some larger screw-type soil anchors that penetrate at least 10 inches and have good bite.

3. If your organic soil is very deep, consider digging through it and installing the anchors into the subsoil. Use chain or wire rope to extend the loops and connect the gazebo to that.

Answer 2

We provide protection for temporary (fabric) structures for “normal” conditions, not “extraordinary” conditions. That is to say, we understand that there will be summer winds that could cause the gazebo to be pushed around, but that when you see a hurricane on the horizon, you’d take it down.

Obviously, the manufacturer is thinking the same way. Those large anchors that have “wide” threads on them are wood screws. (Threads close together are machine screws.) This probably means the frame, sewing of corners, etc. are not designed for extraordinary storms either.

So, based on that, there are two considerations: 1) uplift, and 2) knock over (rotation) on the holddown stakes.

1) Wind can enter the gazebo and want to “escape” so it will push the gazebo into the air. This occurs at about 20 lbs. per square foot or so. To hold it down you’ll need: 10’w. X 12’L X 20 lbs. / 4 corners = 600 lbs. at each corner.

Concrete weighs 150 lbs. per cubic foot, so you’d need about 4 cubic feet of concrete to adequately hold it down. This does not seem reasonable. I’m sure the frame, sewing stitches, etc. would rip apart before this would occur.

Because the manufacturer provided “wood” screws, they are thinking you’ll use wood to anchor the gazebo...not concrete. Screws in “withdrawal” are very weak.

2) It seems pointless to calculate the stress on the gazebo for rotation. (It will be greater than uplift.)

Therefore, I’d use the anchors screwed into a piece of 4x4 about 24” long buried into the ground with the understanding that it’s a temporary structure and ONLY use it in the nicest weather.