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Is this wall strong enough?

  1. Aug 10, 2009 #1
    Hello, as you can likely see I'm new here. I'll be blunt and state off the bat that I am not a physicist or engineer in any manner. Math has never been my strength which is why I spent my university life within the social sciences. I've always had an admiration for those within the natural sciences and their ability to solve more "tangible" issues....which is why I am here. I need to enlist the help of some bright minds for a building project I'm doing in my new, but very small apartment.

    Essentially, my project involves the building of a wall bed/loft bed to optimize my use of space. I want this loft bed to be able to fold into the wall when it is not being used, but I also want it to be up high so that items underneath do not need to be moved when it is folded out. Since it is mounted up high, I am using an electric winch to close it. Think of a drawbridge where the bed is the bridge. It is a queen sized bed roughly 6.5 x 5 feet and opens horizontally. The winch itself doesn't provide any support, I am going to fasten chains at each end that reach full tension when the bed is level. The winch merely pulls it back up. Because it opens and closes, it makes it impractical to use the ceiling joists for support because the chains would be sticking out of the closed bed which closes into a box on the wall.

    My question then is, since the entire weight of the bed, building materials, myself, and my girlfriend would be supported on one wall, is this enough? I've calculated the materials generously at 300 pounds, and should probably alot 400 pounds for occupants, even though my girlfriend and I only weigh about 300 pounds cumulatively.

    The box that the bed folds into will be able to screw into 5 separate 2x4's (studs). The bed would extend about 6 feet outward, given that it is pivoting on hinges on the outer side of the box (which is one foot in diameter). My building materials would be red pine.

    I've attached a poor design sketch to this post. Again, I'm just wondering whether the wall will be able to hold this kind of weight with the outward pull. The chains on each side of the bed are fastened to the box, so as to distribute the weight over the 5 studs.

    I appreciate, any help you guys have to offer, and if anyone has questions about political science in return, I'd be more than happy to help :).

    Thank you kindly.
     

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  3. Aug 11, 2009 #2

    Danger

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    Welcome to PF, Newmark.
    Google 'Murphy bed' first, then come back and see what else needs to be cleared up.
     
  4. Aug 11, 2009 #3

    berkeman

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    Cool Murphy Bed hint, Danger. Thanks.

    Uh, Mark. This is a bed for yourself and your girlfriend. The loads could be quite high, so there needs to be a significant improvement in your structural plans. Can you drop a couple verticals from the bed to the floor when it's folded out? If not, you two are going to have a very awkward surprise sometime...
     
  5. Aug 11, 2009 #4

    Danger

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    Maybe a couple of shock absorbers would be appropriate... :biggrin:
     
  6. Aug 11, 2009 #5

    Vanadium 50

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    And...um...not all the loads will be static.
     
  7. Aug 11, 2009 #6

    Danger

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    :rofl:
     
  8. Aug 11, 2009 #7
    Hello all! :)

    Thanks for your replies. I do realize that this is essentially a murphy bed, but I've been unable to find one online that closely mirrors what I want to do. http://www.moddidaypeople.com/murphy_bed_wall_bed/people_moddi_murphy_beds/Entries/2007/10/11_FAQ:_A_Lack_of_a_Better..._Top_files/modern%20interior%20w-moddi%202.jpg" [Broken] is kind of what I'm thinking, but higher. Essentially I'm trying to combine a murphy bed and loft bed, without the need to have vertical supports.

    I've read that a pine wall stud can hold about 150 pounds, but I'm guessing this is vertical force.

    I also realize that the bed will not necessarily have a "static" load...do to...err...movements and such.

    What if I had the containment box connected to wall studs but made it flush with the ceiling so that it would hit the ceiling joists as well? That way, all of the load would not be on the wall. I've attached another rudimentary schematic (that probably makes engineers cringe lol) to better explain.

    Thanks again.
     

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    Last edited by a moderator: May 4, 2017
  9. Aug 11, 2009 #8

    berkeman

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    I do not think wall studs are meant for bending loads like you are envisioning. They are for compressive loads. Putting some into bending stress like that may compromise their functionality as load-bearing members, which would not be good. You really should convert the loads into vertical loads, preferably with vertical posts to the ground from the outboard side of the bed.

    Is this wall in a house that you own? Or a house/apartment that you rent? Is it a load-bearing wall?
     
    Last edited by a moderator: May 4, 2017
  10. Aug 11, 2009 #9

    russ_watters

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    Those questions imply to me the need for a licensed structural engineer to review the problem. Unfortunately, we don't have one onboard who could tell me I'm being paranoid, but if you find one in the yellow pages and call him, you might get all the advice you need over the phone.

    At the very least, the analysis of the loads needs significant work. The bed might be a 100 lb distributed load, but the occupants would be 300, at worst case, located on the edge of the bed. Due to the angle of the supports (which we don't know...), the forces on the wall are much higher than just 400 lb.

    And while the joking about the potential non-sleep functions of the bed is entertaining, it isn't actually the worst-case scenario for load. The worst-case scenario would be if both people sat down (fell/jumped?) quickly and simultanously on the edge of the bed. The force depends on deformations, but could be vastly higher than just 300 lb. I'd be shocked if the force required at the anchor points was less than 500 lb each. Load bearing or not, it seems to me there would be a significant risk of buckling a single stud with the resulting bending moment of a 500 lb load. Add to that my understanding that you need to cut 3 studs to get the wall to fold into the bed (?) and this project would cause me significant concern.
     
  11. Aug 11, 2009 #10

    Danger

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    Maybe it would be simpler (although not as aesthetically pleasing) to just winch the bed up to the ceiling for extra floor space, and lower it into place on its own legs when needed.
     
  12. Aug 11, 2009 #11
    The anchor points would be into the bed box though and this box would be connected to five studs (16" spacing) over the 7 feet of horizontal width of the bed. So would the weight of the anchor points not be distributed across these 5 studs? Also, I've decided that I could also connect the containment box to the joists in the ceiling by raising it up to that height, so the load would be partially borne by the roof rafters as well, albeit not with complete vertical tension. Does this make enough of a difference?

    Obviously, I don't really want to have my bed crumble in the middle of the night so I appreciate all the advice here and I'm glad I came by. Thanks again.
     
  13. Aug 12, 2009 #12

    berkeman

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    As I think you can tell, you are in the wrong place asking for permission to hack up your house (or somebody else's house). If you do the wrong thing to a load bearing wall, the results can be pretty bad. At the very least, you will need to get a building permit from your city for this, since it sounds like you will be modifying the structure of a load-bearing wall.

    Sorry, this thead is closed. Please do not do this.
     
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