Darryl Keil Last Activity 2025-09-09 11:09 AM
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Tim

Posts: 35

Joined: 2007-06-26
Location: Baltimore MD

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Subject : Torsion box shelf for kitchen
Posted : 2013-09-24 12:26 PM
Post #36998
I need to build torsion bx style shelves for a kitchen. Think shelf full of plates for a load ( to be safe ). Attached drawing will help; 3/4" T & B shelves + 3/8" ribs. Any way to calculate load on screws? I can only assume that no matter how level it is that it will sag from front to back and need to be shimmed a little.
Attached file : Torsion-box.jpg (48KB - 66 downloads)



 
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Craig Mascolo

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Subject : RE: Torsion box shelf for kitchen
Posted : 2013-09-24 3:01 PM
Post #36999 - In reply to #36998
Tim, I built a couple of these recently for a library project. Mine were almost exactly the same dimensions as yours and six feet long. Not sure what screws to which you are referring, but if you mean the rear cleat support screws I used 3/8" x 3" lag screws through a 2x2 cleat and into the studs in the wall. Mine went against a drywall wall, so I removed a horizontal strip of drywall in the vicinity of the cleat and replaced it with a poplar strip to get a good bite with the lag screws. If you can do it, add wall cleats to the ends of the shelves as well. Wax and place the loose cleats in their respective positions during pressing to fill the voids and remove them when it comes out of the bag. Make that grid into a 3-4" square matrix (your drawing shows ribs in one direction only). Generously apply PVA glue all along the grid edges, top and bottom, sandwich it with your 2 pieces of 3/4" material, pop it in the bag and press it. Make sure your platen is dead flat. Install the facing after pressing. Slip the completed box onto your cleats (wax them first) and voila ! You won't have any sag problems. I was able to use mine as a scaffold with full weight bearing during installation. Hope I haven't given you a bunch of info you already know. Just wanted to pass on what I had done.


 
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craig tufankjian

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Location: syracuse ny 13208

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Subject : RE: Torsion box shelf for kitchen
Posted : 2013-09-24 3:40 PM
Post #37000 - In reply to #36998
http://www.italianaferramenta.it/catalogue/wood-and-glass-shelving-systems/traide-xxl.php

installation video on the right


 
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Tim

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Location: Baltimore MD

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Subject : RE: Torsion box shelf for kitchen
Posted : 2013-09-25 12:33 PM
Post #37001 - In reply to #37000
Craig:
Thanks for your reply. I assume the grid internal structure is to ensure stability during glue up. The force exerted when the shelf is installed will only be from front to back ( I think ). You refer to taking out drywall and adding wood to better secure the cleat. I wonder about the compressive force of the bottom edge if it just meets drywall, and whether a wood strip would help there too.


 
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Don Stephan

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Joined: 2003-07-18
Location: Cincinnati, Ohio

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Subject : RE: Torsion box shelf for kitchen
Posted : 2013-09-25 7:03 PM
Post #37002 - In reply to #36998
Tim:

Every torsion box design I have seen has a grid system, not just ribs in one direction. Experiment if you wish.

Craig's reply I think suggested removing all of the drywall behind the cleat, so I'm confused by your question about removing just a strip behind the lower edge, unless you didn't want to remove all the drywall behind the cleat.

Drywall will crush some under the cleat if full torque is applied to the lag screws - I'd expect it's best to remove all the drywall behind the cleat. I would use poplar or other harder wood than 2x4 for the cleat. Just my two cents to an excellent method by Craig 1.

Loved the video, Craig 2.


 
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Tim

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Location: Baltimore MD

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Subject : RE: Torsion box shelf for kitchen
Posted : 2013-10-16 10:56 AM
Post #37025 - In reply to #37002
More questions... In trying to calculate how much leverage is exerted on the bottom edge, does the overall load of the shelf plus plates, etc. get split between tension ( top screws into cleat ) and compression ( bottom edge )? The customer wants to make the shelf 2 1/2" instead of 3" thick. Also, any ideas on routing wiring for LED puck lights. The supply line will come through the cleat and backing plates.


 
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Don Stephan

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Location: Cincinnati, Ohio

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Subject : RE: Torsion box shelf for kitchen
Posted : 2013-10-16 6:30 PM
Post #37026 - In reply to #37025
An architect or structural engineer might be able to help you calculate tension and compression forces.

The cleat should fit near as perfectly as possible against the back of the shelf, so the bottom edge is not carrying all the compression force - most should be transferred from the back edge of the shelf to the cleat.

For wiring, I'm guessing you could drill in from the cleat and up from the bottom for each recessed light. The strength of the torsion box as I understand is the area of glued surface between the grid and skins, but I wouldn't want to weaken the grid any more than necessary.

If you are uncomfortable with the customer's design request, don't proceed. If it fails, seldom does the customer accept responsibility for unreasonable request.


 
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craig tufankjian

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Location: syracuse ny 13208

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Subject : RE: Torsion box shelf for kitchen
Posted : 2013-10-16 8:22 PM
Post #37027 - In reply to #37026
I calculated this once based on the original info you provided (with my CAD) . The shelf will have total collapse after 142 lbs. I did a design (can't find it right now) using steel angle and total collapse was at 1257 lbs.


 
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Tim

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Joined: 2007-06-26
Location: Baltimore MD

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Subject : RE: Torsion box shelf for kitchen
Posted : 2013-10-25 12:44 PM
Post #37031 - In reply to #37027
I have enough time to think up too many questions. If I just use 3/5 VC ply for top and bottom, for example, with 3/4" X 3" front and side edges and ribs as in my original design, are there any forces that necessitate ribs running lengthwise? It will not collapse this way as the front edge will prevent that. This is a project that does not need to be vacuum bagged. Enough ribs will keep it from turning into a parallelogram. The 3/4" material is plenty strong enough to resist both tension and compression. I don't want to make this more complex than needed. I suspect the box type core structure ( cross lapped ribs ) is more to prevent collapse when the faces are vacuum bagged.
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