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Old 02-28-2009, 11:13 AM   #1
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How much weight will a frame support?

I am in the process of building a bunk at the front of my Airstream. I'm really excited with what I came up with, but I have one hurdle left, the mount brackets. I am utilizing a military issue, all aluminum stretcher that collapses down and fits behind the couch. Two of the feet will rest on the front table / shelf area, and the other two will need to be attached at wall mounts I fabricate. I have seen the vintage bunks suspended by cable so I assume there will be no issues, but just wanted to get some input / opinions. Also, how many rivets typically attach such brackets to the frames, and is there any need to beef up the frame structure? It will only be used for children, and my oldest only weighs 50 lbs at this point. I will post some pics once complete, and I think it is going to work out great! Thanks!
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Old 02-28-2009, 11:22 AM   #2
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I don't know what the answer is, but I will share with you what Airstream did when adding bunks to newer units. They reinforced the shell to offset the additional vertical loads. Now what they did and what you are planning sound a bit different, but I would caution you on attaching anything to a rib that wasn't designed for such horizontal loads as I understand you may be looking to do. Since not all the full weight will be supported by the shell (some on a fixed structure) perhaps you will be better off.

Keep in mind I am no engineer.
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Old 02-28-2009, 12:00 PM   #3
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I would'nt use pop rivets by themselves for that. the shear strength is not there for even small children to use it. If it's possible to transfer the load all the way down to the floor, rather than relying on the wall and rivets to hold it up, it will be a much stronger structure. Pop rivets would probably be sufficient in that case.
Pics or a drawing would be helpful in any case, to see what you are dealing with.
Good luck, Rich
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Old 02-28-2009, 12:52 PM   #4
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Look around your trailer and see how the "FACTORY" attached cabinets and other items. You will be surprised at how little the attachments are, sometimes only a sheet metal screw. Those cabinets remain in place while you go tooling down the road with their loads inside.

If you can find vertical frame members I would have no qualms about attaching to them with sheet metal screws, a couple at each attachment point. If the frame of your bunk extends wall to wall at the points of attachment you are talking about a pure vertical load in shear. However if the frame of the bunk is subject to noticeable flexure there will be a pulling component against the screws caused by the for shorting of the frame rails.

If you have to attach at a point between framing I would make plates, say 6x6 ins.,and mount them to the wall before mounting the bunk frame to the new plates. I would hope these plates would be mounted to a point on the wall below the curvature to concentrate the load in shear.

Now you have to remember I carry 2 bikes mounted to the rear of my trailer which is completely against the rules as written by the lawyers at Mother Earth.
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Old 02-28-2009, 12:52 PM   #5
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Error on my part, I should have stated fasteners. When I used to work on aircraft we utilized nut plates which were riveted benneth the frame, then attached various items with screws or bolts. I have not accessed the area where I intend to place the brackets, and I will do a better assesment at that time. I was just hoping someone has been there and done that.
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Old 02-28-2009, 12:57 PM   #6
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I will be utilizing the vertical frame, and the bunk will span the entire distance wall to wall. I think I will be ok, just need to pull panels and take a peek.
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Old 04-26-2009, 03:22 PM   #7
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The bunk is done!!

Please check out the pictures, and feel free to ask questions. I am pretty happy with the way it has turned out. The stretcher is all alluminum construction (Ebay) and it folds down to store behind the couch. Yippee!
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Old 04-26-2009, 06:32 PM   #8
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WVCA,

Nice job, I like it! I guess I'm seeing a "nut plate" in the first photo? Did you buy these and if so could you give the source for them as well as the brackets? Also, I think if it was me I would have attached all four feet to the wall. I remember my son at that age. The front shelf would have holes in it inside of a week!

Carol
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Old 04-26-2009, 06:47 PM   #9
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Looks solid. Did the wall brackets come with it? Do you have any more details?
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Old 04-26-2009, 07:58 PM   #10
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I have 2 vintage Airstream Bunks. I recovered them with ballistic nylon. For the bunk amidships I used a cast aluminum wall bracket. The inboard side in hung from the ceiling using stainless marine fairleads and 1" webbing with some marine catches. The other bunk hangs above the front gaucho Too suspend it I used marine hardware for bimini tops. Cheaper hardware store stuff would work but not look as good. I feel they could hold up to 150 lbs.
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Old 04-26-2009, 08:15 PM   #11
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Looks Great...Obviously your Son approves too.
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Old 04-27-2009, 04:35 PM   #12
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Originally Posted by tallytwo1994 View Post
WVCA,

Nice job, I like it! I guess I'm seeing a "nut plate" in the first photo? Did you buy these and if so could you give the source for them as well as the brackets? Also, I think if it was me I would have attached all four feet to the wall. I remember my son at that age. The front shelf would have holes in it inside of a week!

Carol
Yes the bracket I fabricated in the first photo contains the nutplates. They are 1/4-24tpi, and I Googled nutplates on the net. I think I bought mine from a racing supplier. The mount brackets were fabricated by a machinist friend of mine. I thought about additional mount brackets on the backside, however; there are not frames to support them. My son does't budge them when he is on. I plan to beef up the table at some point, but haven't came up with a game plan yet.
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