Is that Tiedown strong enough?

[Ryanmb21]

When hitting the road we all share some risk of being involved in an accident. Searching accidents on this site or other similar sites reveals this fact.

I've been rear-ended hard enough to total my truck, luckily I escaped with only a stiff neck. I also witnessed someone roll their subaru on the highway in Montana just several hundred yards in front of me. In both instances, and other serious collisions, the forces are great. We all know that.

Which, brings me the question: what sort of tie downs will withstand a serious crash?
- a teenut through 1/2 or 3/4 inch plywood?
- a through bolt to the vehicle with a backing plate?
- a tie down to a piece of metal such as the ones that can be added to the top of ARB outback solution drawers (which are steel)?

I'm curious to try a set of drawers and elevate my fridge above them. I'm either going to buy or build a set soon. I see a lot of excellent DIY and commercial systems built on a tee-nut through material construction. Is this strong enough to hold something heavy? For instance a fridge on slide, a water can, a tool box?

I'm curious to hear your thoughts. Any engineers or people with practical experience? A couple of kids in the back seat have me thinking. This is what I currently have.

Thanks!

 

[volkinator]

Don't have a lot of experience with crashes, but I do know that T-nuts through 3/4" plywood are solid, especially the screw in t-nuts (not the pound ins with the teeth) I've built climbing walls and you can put a ton of weight on them. Even at bad angles with forces about 6" off the main support.

I like your tracks. Do they have a force limit? I feel like I've seen people use them for fridges/coolers,etc. If you tie into your current system, it really wouldn't be too much hard. Thinking off hand, if you wanted it to be totally solid, you could do a couple weld nut backing plates recessed into the top of your drawers? Depends on how permanent you want it to be.

The storage system I am designing, I'll fasten the storage system down to the factory tie-downs, and basically replicate the tie downs onto my system. I'm definitely planning on having everything that has any amount of weight strapped down. Definitely makes me nervous about how they can easily become projectiles.

 

[Ryanmb21]

Thanks volkinator, good info about the screw in teenuts. I don't see people use those often in a truck application. My tracks are from mac's custom tiedowns, I think they said 1000 lbs for each tie down. In my application, I think it would be limited by the factory tie downs or how I have the steel through bolted through the floor.

I would love to see an Overland Journal do a test on tie down strength.

 

[volkinator]

Yeah, that would be awesome! I'd imagine the factory tie downs have to be solid enough for anything we might throw at them. I think they even work similarly to carseat anchors (??) Not sure though.

I'll definitely have to check into those though. I like how you recessed them too. As long as your platform is sturdy though, I can't imagine anything coming undone. Use glue and screws and you should be just fine.

 

[upsidedown2]

I was looking at your pics and since we are talking safety. The welds that I can see in your pics do not look strong or well done at all. If they are just a tac weld ok but what is seen looks week. Need better pics of the welds to tell.

 

[OCD Overland]

Everything in the back of our vehicle is held in place by everything else in the back of the vehicle. If I tried to tie it all down, I'd spend half a day undoing straps at the campsite. Just use a cargo net or some other cargo divider. Most SUVs have factory versions that nothing is going to get through in an accident.

 

[Ryanmb21]

I was looking at your pics and since we are talking safety. The welds that I can see in your pics do not look strong or well done at all. If they are just a tac weld ok but what is seen looks week. Need better pics of the welds to tell.

Thanks for the comment on that, I will evaluate those welds.

 

[Ryanmb21]

Everything in the back of our vehicle is held in place by everything else in the back of the vehicle. If I tried to tie it all down, I'd spend half a day undoing straps at the campsite. Just use a cargo net or some other cargo divider. Most SUVs have factory versions that nothing is going to get through in an accident.

Not tying down gear seems like a horrible idea, tetris'd gear will likely not stay put in an accident. I agree that a cargo net or barrier are a good idea, I use straps and a net. My question is about the tie down point. Is a tie down point constructed with tee-nuts through wood/other material strong enough?

 

[OCD Overland]

I think tie downs are great if you have, like in your photos, one or two heavy boxes or a cooler or something. But it would be impossible for us to successfully tie down the collection of oddly shaped stuff that travels along with us. Here's the cargo barrier we use...

Nothing is getting through that. And if we're talking accidents, I'm not worried about stuff staying put - just not bonking me on the head.

As for whether individual tie downs are strong enough or not, I'd say there are too many variables to go by anything other than instinct. A flimsy d-ring attached to fiberboard with a drywall screw isn't going to do much for a loaded down cooler. On the other hand, military cargo rails and 2" webbing is probably overkill for keeping your sleeping bags from rolling around.

Personally, I'd use a cargo barrier of some sort even if I used tie downs. There's always the chance of something coming loose, or bits of something breaking off and flying around in an accident.

 

[upsidedown2]

The best thing you can do is over build. If you get hit hard or roll hard and stuff starts to move it will rip tie downs out of wood. The big thing is to keep it in it place and not to move. I have seen a small tool box come lose in a wreak and bend a seat back over pop open and stick a screwdriver in the seat. Fire extinguishers come lose and go airborne it will kill you if it hits you in the head.

So things like tools, fire extinguishers,jacks and axes go in a box or tote something you can tie down and keep from moving. Tie down to steel if it takes 2 bolts for a tie down and you go through sheet metal make a backing plate for it. If it is just a stud us big fender washers. Use factrey tie downs and then add to them if you have a roll over or a wreak you will not say I think I had to many tie downs, if it comes lose you will say I should have had more tie downs or stronger tie downs

 

[Rezarf <><]

I agree, a cargo barrier should be your next mod. Separate the kids and the gear with a fixed structure. I agree, in a hard crash things can fail, even solid mounts but if you can keep the junk from contacting people, you win.

Btw, your cargo floor build is one of the cleanest on the interweb, I love it and have had it book marked for years.

 

[rayra]

thru-bolting and fender washers would go a long way towards a reasonable solution to reasonable fears. And a cargo net solves the rest. Or you change the way you pack so the larger dangerous items are tied down and the rest is packed in such a way that only softer things can move about.

 

[DanCooper]

What is the amount of force required for tear through?

I looked at your build for storage, and as so many have said, it is beautiful. The tie down rails, as I understand it, are bolted through the floor (or perhaps more correctly, are bolted to steel cross-members which are bolted through the floor). The bolts through the floor are backed by fender washers. Assuming you used grade 8 bolts in bolting the entire structure together and through the floor, it seems to me that the most likely point of failure would be at the floor penetration, either the fender washer wasn't large enough, or the fender washer was of a material that allowed the bolt head or nut to tear through. Once again, I assume grade 8 hardware was used for the washer. If so, you need to get one of the engineers on here to calculate how much force would have to be generated to allow the nut to tear through the fender washer. I would imagine that the engineer would have to have some more info, such as the mass attached to those tie down points, as well as the size of the fasteners.

Thanks for starting this thread, as it made me stop and think about what I am getting ready to do. And once again, I think your track system is gorgeous.

 

[DanCooper]

Dang it, you made me start thinking, and I couldn't stop.

I don't think I touched on your original question, which seemed to have more to do with the construction of a container than attachment to the vehicle. So I started thinking about whether there are two problems presented in your question. First, what is the strength of the attachment point of the retaining device or structure to the vehicle, and second, what do you do to assure the structural integrity of the container?

A grade 8 nut and bolt have a tensile strength of 150,000 psi. (see, e.g., https://www.boltdepot.com/fastener-information/materials-and-grades/bolt-grade-chart.aspx) Fastening the retaining device or structure to the vehicle with grade 8 fasteners should keep that device or structure firmly attached, assuming it is properly backed and tightened (over tightening will potentially weaken the bolt and nut). An excellent, albeit lengthy, paper by Fastenal on these types of mechanical fasteners is found at https://www.fastenal.com/content/documents/FastenalTechnicalReferenceGuide.pdf After you get the device or structure attached to the vehicle, the next failure point will be how you attach the container to that device. Straps all have their load rating attached, and turnbuckles and mounting rails also publish the loads they are designed to withstand. Once you look at all your components for restraining your container(s), you should have a good idea of how much force it is going to take to set the container adrift.

But then I was thinking about wood construction, and tee-nuts, and tear out, and how would one go about building a wooden drawer system that would stay together in an accident? Mechanical fasteners in wood are interesting, because a number of factors are in play, including the wood, whether the wood is solid or otherwise, the orientation of the wood to the joint (i.e., lap, butt, rabbet, scarf, etc.), and the type of fastener; screw, bolt, adhesive, or other. Lots of alternatives, yes?

For fastening with screws, here is an interesting paper: http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch07.pdf Once again, lengthy. This chart is easier to read: http://www.screwdoctor.com/application/home/selection_guide/technical_data.aspx Keep in mind that the question we are considering includes both tensile (tearing apart) and shear (breaking the long axis of the fastener) components.

What happens when you add an adhesive to a wood (or any other) joint? It generally gets stronger, and the joint is better able to withstand both types of forces (greater shear and tensile strength). There are many, many articles available on this, for example, https://www.freemansupply.com/datasheets/adhesivesguide.pdf provides an overview or introduction. From there, the possibilities abound.

After thinking about it, I think I will likely build my boxes out of plywood using mechanical fasteners, and reinforce the joints with something akin to a fiberglass tape. Fastening the boxes to the vehicle will be via grade 8 fasteners through bolted through the vehicle's floor, with appropriate grade 8 backing plates, properly torqued. And a net between the passengers and the load. And the rest I will leave to chance.

 

[Ryanmb21]

...
Thanks for starting this thread, as it made me stop and think about what I am getting ready to do. And once again, I think your track system is gorgeous.

...

Btw, your cargo floor build is one of the cleanest on the interweb, I love it and have had it book marked for years.

Thanks for compliments fellas - I appreciate the nice words!