Storm Shelter Concrete Anchors 1

[geauxLSU]

Hello,
I'm an EE in the market for a steel storm sheltered to be anchored to my garage floor. I've read the Hilti datasheets/specs (HUS-EX & Kwick Bolt 3) and basically anything with a diameter => 1/2" and a >2" embedment requires a 5"-6" slab, but the standard house is 4". To meet Fema 320 specs you need to be about 3". From all the research I've done, all the storm shelter manufacturers are violating the Hilti datasheets big time, which puts me on edge. I feel like its just a guessing game now if the anchor will hold since they a either completely going through the slab or not leaving any room below the anchor. One prominent company uses 7" anchors which will rust out since they are in the dirt!

Does anyone have any advice? The shelter certification companies have basically told me they don't care, go away.

Thank you

 

[concretemasonry]

geauxLSU -

Apparently, the shed is inside a garage (or is it an open carport?).

Do you have a building code that has adopted the FEMA suggestions? If not, FEMA is only a suggested method since has to be adopted by someone to give it some enforcement power. Unfortunately, some standards are not written in "code enforceable language, so that is why they are not adopted by a legal authority. I see this very often sitting on code committees and working with associations that desire incorporation in a recognized code.

If it is not accepted by your code in some way and not up to local code enforcement, it is up to the shed building system company to supply instructions on how it should be installed. If it blows away and is in your garage, you may also have to determine if it covered when they find it along with Dorothy in Kansas.

The details and specific discussed and great technical items, but difficult to relate to a small shed in a garage. The shed manufactured (if he is not installing it) supply sufficient details of attachment and base since that is the only way to have some guarantee.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[XR250]

I think you need to go the epoxy anchor route for sure as expansions anchors cannot go that deep into a slab without risking spalling out the bottom.
Does not seem to bother car lift manufacturers as they install these all the time in 4" slabs with expansion anchors.

 

[geauxLSU]

Dick,

Builders/Installers are required by the NSSA and ATSA (storm shleter assiciations) to follow FEMA guidelines and pass a debris impact test at Texas Tech. Interestingly when you look at these documents, there aren't any rules for strictly steel shleters. FEMA 320 specs wooden and concrete shelter. So its a bit of a joke that they advertise meeting FEMA specs. I'm less concerned with the structural strength becasue I've seen so many impact test, including cars driving into them at 50mph.

But, anchoring is still a concern. They may be not be anchored correctly becasue the anchors are design for 6" slabs and most are knowingly using anchors that will rust when exposed to the dirt/moisture underneath.

Everyone tells me I just thave to trust the installers, but if they are violating the specs and using anchors that rust, its hard to get comforatbale with that.

Do yall think anchor threads embeded in concrete could rust if the bottom of the concrete has a hole? I know the anchor will rust, but it seems the rate is slow so the length of the bolt is not a concern, just the threads embedded need to not rust.

 

[TLHS]

Anchoring doesn't help you if your slab isn't strong enough to actually engage the amount of weight you need to keep your shelter from blowing away. So, while you have to solve that problem it may not be the only one.

You can install whatever anchorage you want, but if the concrete around it rips apart it's not going to help you. If what's being tied to doesn't meet the requirements of the vendor's typical installation, a structural enginer needs to design anchorage and possibly foundation/slab modifications for your specific situation. This may or may not be the vendor's problem, depending on what the agreement you have with them says.

 

[dhengr]

GeauxLSU:
Read the fine print on the shelter’s manufacturer literature. It likely says they have tested the shelter and it meets FEMA Stds. when it is properly anchored down. And, they may actually have done some testing to back this up, under a standardized protocol. Then they leave that foundation (tie down) design problem to a third party, and if anything goes wrong they will argue that it was not tied down properly by you or your installer. They’ve sold their shelter units, made their money, paid their insurance premiums and will take their chances. When they are mass producing and commoditizing something like this, there are just too many variables in the way of existing soil, foundation, terrain conditions, etc., for them to design the foundation for the shelter. They would be sticking their neck out even further doing that, than the way they are doing it now. We can’t really help much either, for the same reasons, we don’t know enough about the prevailing conditions, and it seems you’re not so sure either. I think you should find a local Structural Engineer to help you with this problem, someone who knows the local soils conditions and can inspect your bldg.

 

[concretemasonry]

Much/most of the impact testing that is used is done at Texas Tech the standards for projectile penetration (the largest cause of deaths from tornadoes) are for penetration of a wall assembly in the lab. The vast majority of the accepted walls were reinforced block or reinforced concrete until a wall assembly. After many years a wall assembly using 2x6's (12"oc.) sandwiched with a sheet metal plate and 3/4"" plywood was accepted for FEMA projectile approval. That research is the basis for most FEMA suggestions that are incorporated into a legally enforceable standard. I do know know whether FEMA has done full structure testing for entire structures. They do however, have plans for tornado resistant structures that are reinforced concrete block or reinforced concrete including the roof assembly and the connection to the concrete slab including slab thickness requirements. These are used where structures must have a tornado resistant structure (free-standing, inside a single story home or in a basement. - It is good information. The guys in the labs seemed to have a good time shooting the 2x4s out of an air cannon.

If the steel building company is to be responsible for the hold down of a structure they must build according to whatever standard they claim it will work for. Somehow, the small building suppliers and their sellers do not seem to have a good "handle" the wholes structure below the base, but they are responsible for their suggestions. Your trust in them is based on them being lucky or using a standard that include some sort of code language or if the are self insured.

The bolts should not go through the concrete and into the soil because the corrosion is more severe. that is why there are concrete coverage requirements in codes to prevent corrosion and protection.

Personally, the the only problem is not the shed flying away. There could be some damage on the ground if the shed breaks away somehow if the garage does disappear. Professionally, I would accept better information of just design the connection to the concrete myself since it would be my money.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.