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Angled leg strength

Sean_a's picture

Angled leg strength (post #169146)

Sean_a on Tue, 09/13/2011 - 16:52
in

I'm working on a table design and am trying to see if I can do angled legs like an 'x' withoout the top portion. (see photo). The table would function as a desk so I'm not trying to get to withstand a huge load but it should be sturdy.

 Is there a way to calculate the strength of the table on side furthest from the legs?  Or is this something that won't work.

-A +A
RalphBarker's picture

cantilevered designs (post #169146, reply #1 of 2)

by RalphBarker in reply to Sean_a [original] on Wed, 09/14/2011 - 08:05

I'm not a structural engineer, but there are numerous examples of cantilevered desk designs. In general, I think you're dealing with some combination of "shear" strength, and "bearing" strength, depending on the design of the joinery. For example, if the primary leg is simply attached to the edge of the top, you're working only with the shear strength of the materials and/or the attachment hardware, dowels, etc. That is, how much force is required to split the components along grain lines, or shear off the hardware. If the leg is also inside a large dado in the edge of the top, bearing strength is added to the equation.

I have no idea of how to actually calculate the design strength, however. That would involve both calculations for the materials being used (e.g. oak vs. pine or poplar), and the joinery (e.g. glued faces, supplemented by screws, dowels, etc.).

PSeverin's picture

Joints (post #169146, reply #2 of 2)

by PSeverin in reply to Sean_a [original] on Wed, 10/19/2011 - 11:11

It has been too long since the structures classes, but this is wood.  Wood is forgiving.  I would suggest that you build one leg and test it yourself.  See if the joints between the top, short leg and sloped leg works.  Lean on it.   It is going to bend, deflect as the engineers say.  But how much is acceptable to you is the question.  

I'm as much worried about the lateral stability, how you link the pair of legs so that it doesn't sway side to side.  Once again it is the joints and how rigid you can make them that I see as more of a problem than the strength of the wood.   

This sort of question could be analyzed by engineers and give you a bunch of probably answers, with safety factors for different species of wood.  But the problem is usually solved in the old trial and error method.  The Mexican architect Candella made some amazingly thin saddle shaped structures, some 1 cm think.  How did he know they would work.  He had his students form test structures  and if they failed they made it thicker and learned.  Then he built the churches.  Math can get in the way.  Make it , break it and let us know what you learned.

Peter