Will My Cantilevered Countertop Design Prevent Sagging?

[Enrique Lopez]

Hi all, I'm new to the forum and need some help. I am a drafter at a millwork company and need some assistance for a cantilevered wood countertop. we need to cantilever a 3/4" thick walnut countertop and I have designed a metal frame to support it but I need to verify if my design will work so the cantilevered area will not sag. the frame is made of 2" x 2" steel tube with 1/8" walls and will be anchored to the concrete floor. I also added an angle metal diagonally to give more sturdiness but I am still worried with the weight of the counter that it will sag. If someone can help me out and maybe give me the formula so I can figure it out for future project that would be great. Let me know if you require more info.

 

[lewando]

Not an ME, but a few questions:

In addition to the weight of the counter (potentially causing some sagging), what is the maximum expected loading of unidentified stuff that someone will put on the counter?

How much sagging can you tolerate?

 

[Enrique Lopez]

Thanks for your response Lewando,

on top of the counter we are only expecting small items like cups, mugs, plates etc...its like an eating counter.

 

[bsheikho]

I did a quick Solidworks simulation of your part, everything checked out in terms of failure. I used an arbitrary value of 100 lbs force on the furthest edge, it seems like it can support it, though it doesn't take into accoutn constructio of the table such as welding type. Also it does show that the end of the cantilever you would have some deflection. I guess it is shaped this way because it needs to be, and doesn't sound like you would place 100lb of material on the table, so it should be fine.

http://imgur.com/a/YogSb

 

[lewando]

Those items represent expected loading, but you should consider reasonable unexpected loading. What if someone accidentally sits on the shelf? What if a couple of people decide to engage in activity that sets up an oscillation on the shelf?

I think a cantilevered shelf will always have some amount of load induced deformation so that is why I ask how much you can tolerate. Design tools will likely ask for a tolerance as an input or tell you what it will be based on other inputs.

Please be concerned about human safety under all conceivable use cases no matter how insignificant the structure.

 

[256bits]

Thanks for your response Lewando,

on top of the counter we are only expecting small items like cups, mugs, plates etc...its like an eating counter.

I was just looking at the near horizontal beam, 56 inch length, attached to the middle upright, and modeled it as a simple cantilever.
For a load of a 100 pounds at the end of a 2inch box bean cantilever, mild steel, one would expect a deflection of around 1/2 inch, give or take.
I did not take into account that the upright will also defect, thus amplifying the deflection at the end of the counter.

How much deflection can your customers deal with?
How much vibration can you customers deal with?

 

[CWatters]

If there a reason why the metalwork isn't symmetrical? eg same on the right of the vertical post as the left?

 

[Nidum]

@Enrique Lopez

(1 ) An effective cantilever has to have a strong root fixation . That fixation is notably absent from the proposed design .

(2) The arrangement shown could twist as well as simply deflect .

If there a reason why the metalwork isn't symmetrical? eg same on the right of the vertical post as the left?

Tell us what the actual requirement is . It may be possible then to suggest improvements to the proposed design .

 

[Enrique Lopez]

The reason it is not symmetrical on the right is because there will a wood die wall and cabinets that will ultimately wrap around this entire metal structure and will hide the metal. I did not include that in the design as it serves no support whatsoever, it is simply to hide the metal. Basically where the vertical legs end is where the wood die wall would end.

The customer is aware of SOME deflection but would like it to not be TOO flimsy. People will be sitting around the ctop and would most likely lean on it as they stand up (human nature). What I am really interested in is to find out an equation on how far I can cantilever before it starts to sag.

As for this one, we are pretty much stuck with the dimensions.

 

[rbelli1]

far I can cantilever before it starts to sag.

The pedantic answer is zero unless you get infinitely strong material. As others have asked how much is too much?

BoB