4 pounds over the weight limit of a tv stand

[saturnv123]

I wanted to put a 39-pound tv on this tv stand: https://www.ikea.com/us/en/p/lack-tv-unit-black-brown-00566060/

The weight limit of top shelf is 35 pounds, but my tv weighs at 39 pounds.

Is there any way I can adjust the force distribution so the shelf can hold my tv? tv has 2 base legs about 40 inches wide.

 

[erobz]

I wanted to put a 39-pound tv on this tv stand: https://www.ikea.com/us/en/p/lack-tv-unit-black-brown-00566060/

The weight limit of top shelf is 35 pounds, but my tv weighs at 39 pounds.

Is there any way I can adjust the force distribution so the shelf can hold my tv? tv has 2 base legs about 40 inches wide.

You can't really adjust the force distribution ( you could add material , but...) for what its worth the image is referring to a concentrated load of 35 lbf at the center of the span.

If your TV is like mine its on 4 legs situated just a few inches from each edge. So, it would be approximately this loading.

That's a favorable loading scenario in comparison.

Also, I don't know if I'm being dramatic, but I operate under the premise that the TV
weighs around 40 lbf. and the spec is for 35 lbf (they are using kgf instead of Newtons).

 

[berkeman]

Is there any way I can adjust the force distribution so the shelf can hold my tv?

In addition to the comments above by @erobz it should be pretty easy to add some strength to the stand by attaching a panel to the back that overlaps the top, middle shelf and sides. That will help to prevent any racking failures of the stand, which is probably the main failure that they are thinking of with their weight rating.

Be sure to pre-cut whatever holes you think you will need in the back, and paint it "LACK" to match the rest of the shelf.

 

[russ_watters]

The drawings contradict each other: is there a center post on the bottom or not? If not, you can add one both under and over the bottom shelf to reinforce it(if yes, just add one above). I've done this. Note: the top shelf may sag a bit if not braced, and that sag may increase over time.

 

[saturnv123]

You can't really adjust the force distribution ( you could add material , but...) for what its worth the image is referring to a concentrated load of 35 lbf at the center of the span.

View attachment 352790

If your TV is like mine its on 4 legs situated just a few inches from each edge. So, it would be approximately this loading.

View attachment 352791
That's a favorable loading scenario in comparison.

Also, I don't know if I'm being dramatic, but I operate under the premise that the TV
weighs around 40 lbf. and the spec is for 35 lbf (they are using kgf instead of Newtons).

Thank you for the explanation. Yes, my tv will be like what's drawn in the second pic, about 20 lb each side (39 lb in total) but the total weight limit should be 35.

 

[erobz]

Thank you for the explanation. Yes, my tv will be like what's drawn in the second pic, about 20 lb each side (39 lb in total) but the total weight limit should be 35.

The point of application of loads are significant. Loading as the second diagram will result in less peak stress and deflection in comparison to a peak load as specified in the drawing. They should be specifying worst case loading in the drawing. Your TV is likely going to be supported near the ends of stand.

 

[Baluncore]

Your TV is likely going to be supported near the ends of stand.

I agree.
The legs and joints look stronger than needed, so it is safe to assume that the mode of failure will be progressive flexing of the top shelf.

From the moment point of view, 35 lb at the 1/2 way point, can be split into two point loads of 17.5 + 17.5 lb at the same 1/2 way central point.
If those point loads are separated, and brought back to the 1/4 and 3/4 way points, they will support 35 lb at each of those points, due to the lever arm advantage. That is sufficient to support a two legged 70 lb TV on the two separated points, since 70 lb / 2 = 35 lb.

 

[Tom.G]

In addition to adding a back panel as @berkeman suggested, you can add reinforcement on the front and/or rear edges of the top shelf.

I have had good luck with those low-cost bookcases made of wood-chips-and-glue when I added reinforcement of metal U-channel to the edge. For lighter overloads, just an "L" shaped aluminium strip is sufficient. Use plenty of short sheet-metal screws about 2.5 to 3 inches apart. Sheet-metal because they are threaded full length and the threads are cut deeper.

U-channels I've used are the ones for putting adjustable shelves on the wall.
Here in the U.S. they are available in Steel or Aluminium.

If using an "L" shape reinforcement, put one surface on the front or back edge and the other on the bottom side of the shelf. Put the screws into the bottom surface.

For a U-channel strip, put the shelf in the channel. I find that putting the screws in from the edge works fine; the sides of the U-channel prevent the shelf from splitting. (providing there is a good fit!)

Cheers,
Tom

p.s. Since I'm in earthquake country, I've found the added strength of gluing the joints, when practical, is worthwhile.

 

[sophiecentaur]

I'm pretty sure there's nothing to worry about but ....
The first picture that came into my head was a thin vertical black steel rod, passing through the centre of the bottom shelf (or under the CM of the TV?) with a plate each end directly supporting the table. The top plate would be invisible (underneath the table top) and so would any adjuster (threaded hole down the middle and a M10 bolt supporting the table) A 15mm rod would almost support your car and a 10mm threaded hole down the centre would be easy to drill, centring wouldn't be a problem if you're careful. Square 'offcuts' are available but circular plates of all sizes can be found on dear old eBay.
I have a stand with three glass(!!!) shelves. It has three legs (made up of tubular sections) and the central leg is near the back and takes a lot of the load. It scares me a bit but even our bigger TV is still sitting up there.

 

[saturnv123]

The point of application of loads are significant. Loading as the second diagram will result in less peak stress and deflection in comparison to a peak load as specified in the drawing. They should be specifying worst case loading in the drawing. Your TV is likely going to be supported near the ends of stand.

So here's how my tv stands. 4 pounds over the weight limit, so each tv leg has 2 pounds over the limit.
I may come back to update periodically how the stand is doing.

I suspect the stand will sag/bend eventually because time is another factor that I haven't considered.
Force × Time is more unpredictable. But let's see.

 

[Baluncore]

That looks like an ideal solution.
The TV legs are so close to the ends, that there will be no sagging.

 

[russ_watters]

I suspect the stand will sag/bend eventually because time is another factor that I haven't considered.
Force × Time is more unpredictable. But let's see.

I agree with @Baluncore . I mentioned sagging, but my TV that sags its shelf is on a single stand about a foot wide, in the center of the shelf, not on two legs at the sides. Your setup is near perfect, and will not sag.

 

[erobz]

Just for the torture of it...Here is the approximate loading of the top shelf:

The elastic curve is given by:

$$ EI y(x) = \frac{P}{12} x^3 - \frac{P}{12} \langle x- a \rangle^3 - \frac{P}{12}\langle x- ( L-a) \rangle^3 -\frac{Pa}{4}( L- a)x $$

You evaluate at $L/2$ for maximum deflection (symmetric loading)and compare with max deflection of simply supported beam center point load ( same load - commonly found in textbooks, etc...)$y_D = -\frac{P}{48 E I}L^3$

You will find that your peak deflection $y_A$ is at about 15% of design maximum deflection of the design loading.

feel free to measure the distances of $a$ if you see the need and re-evaluate.

The angle braces $\langle \rangle$ are the Singularity Function ( that is zero for negative value and itself for positive values ).