Holding Down Shelter - Structural Engineer Needed Please

[BMQuinn]

Hi there, I'm hitting a wall with this. We need somebody who can tell us what type of fasteners we need to hold down our camp shelter. The shelter is 30 feet wide, 80 feet long and 15 feet tall with arch type hoops every five feet on center holding up the PVC cover. Placement says to look on the Hive and Spark, I did that found nothing.

We want this year to be our first go at this new camp but if this does not get resolved soon we will be forced to cancel this year. I reached out to a structural engineering firm in Reno but they had no idea what the holding power of 18 inch long lag bolts was, they quoted many thousands to figure out what was needed and we do not have the time for them to learn how to do this.

There must be a structural engineer who is in this community and they know what is needed. We need someone with experience, many many many shelters go up each year there MUST be a sticky somewhere that says what to use so the anchors are stronger than the shelter frame making sure it does not blow away and kill hundreds, I know I know safety third but seriously sharp metal poles could really do a lot of damage if they turn into a massive sharp killer tumble weed!
Please Help!
This is our brand new shelter for our space.

https://tmgindustrial.ca/products/30-x- ... ough-doors

[Sham]

I'm not a structural engineer, but I've seen a lot of similar structures on the playa. I am wondering if there are holes for lag bolts on this structure? A quick count looks like 50 lag bolts would hold this down pretty solid. You can go as long as you wish on the bolts, but I found that 12" lags are extremely snug.

[burner von braun]

Here is a deep eplaya rabbit hole for you to dive into BMQuinn...

https://eplaya.burningman.org/viewtopic ... 77&t=68556

...and good luck with your camp!

[DoctorIknow]

Did you read the link above?
There are many posts about what is used out there for the biggest of structures.

I'm now engineer, but perhaps every 20 feet on bot sides one of those very large screw in anchors, and then between them, 18" lags.

You should be worried about the structure going airborne.....so make those tie downs so strong that the fabric could be ripped apart without being a sail lifting off the ground.

Good luck

[some seeing eye]

I am not a structural engineer.

Two pieces of data for your engineer:

https://eplaya.burningman.org/viewtopic ... 7#p1093297 post by Mr Shoeshine in the big Figjam lag screws topic

and

https://www.washoecounty.gov/building/C ... ements.php

The measured wind speed is at https://www.wunderground.com/dashboard/pws/KNVLOVEL7 on the calendar, you can go back to previous years. 2022 was a bad wind year.

Very important, be sure to remove your anchors. They are a growing source of MOOP - things left and not removed. They are very dangerous, if someone hits one driving across the playa the rest of the year at speed, it is an instant flat, and possibly a flipped vehicle.

Good luck!

[Father_Burn]

Not a structural engineer...however.
We used the same type of structure last year, just a 30ft long wind and snow load rated portable garage.
We used 1/2" X 16" lags sunk in by a 1/2" drive dewalt impact. It didn't budge. Does that mean yours won't, no...but what else are you going to do?

I did try to put some angle on it as it went in, as stakes in the ground have more strength sideways.

If you're really worried, get some large webbing straps and penetrator earth screws and put some safety straps across it in a few points to make sure... Make sure you angle the screw to the load.

Reach out to the suspended animation camp. They used to do a class on tying up your camp...maybe they still do.

The question I'd ask is why that particular structure? I know it's kinda late to change plans, but from experience, we are NOT bringing ours out ever again. They are too much work to put together and take apart. I would have a mutiny on my hands from my camp if I tried.

You may want to think about the flat top structures made of EMT that most everyone uses. Flat structures don't have Bernoulli effect like curved top structures. You'll save a grip of money, and probably be cooler because you can make it out of shade cloth so the heat doesn't build up inside...

[Popeye]

Not a structural engineer...however.

I did try to put some angle on it as it went in, as stakes in the ground have more strength sideways.

I have to disagree with you on putting an angle on lag bolts. With rebar, yes and angled stake holds best. But the holding power of lags comes from the thread, not so much from the friction on the rebar/stake.
To demonstrate, drive a nail and screw a screw into a piece of 2x4 and use a claw hammer to pull them out. The screw will take a lot more force to extract.

[FlyingMonkey]

2017 was a bad wind year for my camp. Not so much constant high winds but one very strong down burst that hit us head on. We use the standard 10' x 20' carports that are popular.

We "always" put 14" lag bolts on each leg and sometimes use cargo straps as guywires for additional security.

When the wind hit us it was a rapidly moving orange dust storm. Me and some camp mates saw it coming and jumped up to grab the horizontal bars of the carport. I was actually lifted off the ground and almost had to let go for fear of going kite sailing.

The storm hit hard but passed quickly. Somehow we neglected to secure one of our carports and it was lifted up in the air and came down in a heap of twisted metal frame pieces. The wind was so strong that my carport (which was well secured) was lifted a few inches and the unions where the legs insert were bent basically turning it in to a slight parallelogram.

I have a lot of respect for the Playa wind that can even appear during an otherwise calm day.

Some of the changes we have implemented since the 2017 wind storm are:
- Make sure every leg post is secured with a 14" or longer lag bolt
- bungee legs of adjacent car ports together for additional support
- secure tube unions to their opposing post feet using straps in an "X" pattern
- only use 1/2 or fewer of the bungee balls to secure the roof so they are the "weak link" in the structure and the roof tears off before the structure fails

We were very lucky no one got hurt when our carport went completely airborne. We have not had any wind failures since then.

[RodMcInnis]

I am not quite picturing your shelter. You said it was 80 feet long and 15 feet tall. Are the sides open, or do you have a wall that is 80x15?

A structural engineer could probably tell you what the tensile force strength of a lag bolt would be, but that wouldn't really apply as the bolt would pull out of the ground well before it broke. The playa gets really thick just a few inches down so a lag bolt will hold reasonably well, for a while.

You can also get "screw ground anchors" that are like a lag bolt with much more aggressive threads. Don't get the ones intended for sand, they won't thread into the playa well at all.

My biggest concern of your setup is the wind load on a 80x15 'sail'. There is a prevailing wind direction, but you must prepare for any wind direction, especially when a dust devil blows through your camp. For that large of a wall I would expect that you would need a lot of lateral support, such as straps from the top of each support post going down at a 45 degree angle to an anchor.

You may also have a situation where the wind blowing over the top of your shelter creates lift. I combat this situation by driving a 4' length of rebar 3' into the ground and then use a hose clamp to clamp the rebar to the legs of my shelter. A T-stake would work even better.

[Sham]

https://www.tmgindustrial.com/products/ ... ough-doors

[DoctorIknow]

-------- secure tube unions to their opposing post feet using straps in an "X" pattern

I've used cross bracing with mule tape aka: pull tape, on three sides AND below the roof tarp. Of course, pull down ratchet straps on all 6 legs of the 12x20 BlackRockHardware shade structure. (That "extra" 2 feet means more coupling$s, but makes such a difference.)

Also, 18" lags all around. Some years I've been the first 6 inches of playa surface is useless for grip.

[trilobyte]

I'm not sure there is an easy answer to your dilemma.

What you're designing, 80 feet by 30 feet with a 15 foot height... is really quite significant. And a PVC cover, which is generally going to become a sail depending on the design of the structure and how everything is attached and connected. What you need is a structural engineer who is a core member of your team who has enough experience with playa conditions that would be capable and willing to do it and ensure everyone's safety.

I can tell you that you almost certainly need something stronger than a standard lag bolt, I'd look for something like a 24+ inch auger bolt/anchor with some combination of airline cable/rope for rigging. I've designed and built over a hundred shade structures over the last 20+ years at Burning Man, and I wouldn't touch something of that size. It's a function of cost and risk. As the structure size goes up, they become more difficult and costly to anchor. And the larger a structure becomes, the greater the risk in the event of failure. Remember, whatever structure you build on the playa has the capacity to become airborne and cause injury to one or more persons, as your design gets bigger so does the risk and potential for damage.

Good luck - get an experienced person on board your team, or perhaps take a different approach with a number of smaller and more manageable structures.

[Popeye]

These links might give you some information. Torrey Smith did a lot of work regarding pull out of different types of stakes.
https://eplaya.burningman.org/viewtopic ... t#p1149543

https://eplaya.burningman.org/viewtopic ... ut#p904118

https://eplaya.burningman.org/viewtopic ... e#p1126672

[trilobyte]

Good links there, he and the Sextant Camp team did some good testing. Torrey was holding down some quite tall towers, and if I remember from his build on playa the 3 foot anchors did quite nicely for his purposes. The benefit on an auger anchor is it can get a much better grip in the Earth (the image below is a 20 inch auger anchor)...



Where a lag bolt is largely just a long threaded bolt or screw....



Depending on the playa conditions in any given year in a particular spot on the playa (and it does vary from one area to the next), the playa surface will be from zero to several inches of dry, flakey bits of dust. 14 and even 18 inch lag bolts driven with an impact driver may sound like quite a big anchor, but only about half of it is going into any kind of hard pack. Also, because of the smaller bolt-sized thread, even if it gets a really good grip it's only going to have so much hold before it pulls out. The much wider thread on the auger does a much better job securing much stronger lines.

Using auger anchors can be a bit more involved than a lag bolt. While you can use an impact driver or decent hammer drill to drive lag bolts into the ground, augers are more substantial. I use some for some of the structures I have at home in southern Nevada (not because of giant structure as much as because of the kind of soil I'm working with on that part of our property), what I use are little babies compared to what a large structure would need. On smaller augers you can usually drive in manually by putting a piece of steel through the eye and turning to drive it down. Longer augers may require a more specialty bit or more powerful tool to drive them in. It can be easy enough to figure out, just a matter of figuring out the exact anchor you'd need, then looking up the best tool options to put them in and take them out.

All that said, it's worth repeating that you should have an experienced structural builder on your team, and not just running with something based on a web search or message board thread. Sextant camp's videos and pics make things look easy, but remember they had a number of experienced designers and engineers on their team.