Engineers needed - glass table max load
Discussion
Hi,
Anyone know the maximum load I can put on a 6mm thick BS6206 glass table?
Dimensions are 1m length front, 560mm depth, 500mm length back.
Has supports at each corner.
Want to put my LCD TV on it but it weighs about 50lbs and I would cry very much indeed if it fell off due to the glass cracking.
Thanks for any info.
Anyone know the maximum load I can put on a 6mm thick BS6206 glass table?
Dimensions are 1m length front, 560mm depth, 500mm length back.
Has supports at each corner.
Want to put my LCD TV on it but it weighs about 50lbs and I would cry very much indeed if it fell off due to the glass cracking.
Thanks for any info.
This is not exactly an easy thing to calculate I'm afraid. Someone with access to and the skill to use an FEA package might be able to do it.
FWIW I would guess that the BS for glass table would be for it not to break if a person fell onto it. If this is the case, it will support your 50lb telly no problem.
You could put a 50lb weight on it and see what happens, if it doesnt break straight away it porbably never will.
FWIW I would guess that the BS for glass table would be for it not to break if a person fell onto it. If this is the case, it will support your 50lb telly no problem.
You could put a 50lb weight on it and see what happens, if it doesnt break straight away it porbably never will.
There is probably a government standard for testing and materials where you can look up the stregth of the material. In America, its ASTM (American Society of Testing and Materials), and they have standardized testing and numbering system for materials. For a quick guess, you can find the strength and see how much your TV weighs to get some idea.
However, the listed strength may not be the same strength for the condition of your loading. Also, the way materials are assembled (location of supports) will determine where and how much stress is applied, and certain arrangements will be stranger than others.
The yield strength is the stress (force per area) when it begins to break. A material can have a different yield strength in tension or compression or bending, and these are usually listed for values most commonly needed. Like concrete will have a yield listed for compression but maybe not for tension. You can find the bending stress applied to the glass by figuring out the weight (force exerted by the TV) and moment the TV exerts as it tries to bend through the cross section of the glass. Bending stress is based on the moment exerted by the TV (quick and dirty is to assume a concentrated mass acting through the center of gravity of the TV at a distance from the load to the support of the glass), divided by the area moment of intertia of the cross section. That distance times the weight is the moment. It's actually a distributed load, but that's too complicated to figure out.
Bending stress = My/I, where M is the moment, y is half the thickness of the glass (through which the bending occurs) and I is the area moment of inertia of the cross section of the glass. I= (1/12)*base* height^3 where the base is the width of the glass table and height is the thinckness. Calculate stress where the longest moment occurs, as this is where it will be weakest.
If the yield in bending is listed, you can compare this to the bending stress you calculated.
However, the listed strength may not be the same strength for the condition of your loading. Also, the way materials are assembled (location of supports) will determine where and how much stress is applied, and certain arrangements will be stranger than others.
The yield strength is the stress (force per area) when it begins to break. A material can have a different yield strength in tension or compression or bending, and these are usually listed for values most commonly needed. Like concrete will have a yield listed for compression but maybe not for tension. You can find the bending stress applied to the glass by figuring out the weight (force exerted by the TV) and moment the TV exerts as it tries to bend through the cross section of the glass. Bending stress is based on the moment exerted by the TV (quick and dirty is to assume a concentrated mass acting through the center of gravity of the TV at a distance from the load to the support of the glass), divided by the area moment of intertia of the cross section. That distance times the weight is the moment. It's actually a distributed load, but that's too complicated to figure out.
Bending stress = My/I, where M is the moment, y is half the thickness of the glass (through which the bending occurs) and I is the area moment of inertia of the cross section of the glass. I= (1/12)*base* height^3 where the base is the width of the glass table and height is the thinckness. Calculate stress where the longest moment occurs, as this is where it will be weakest.
If the yield in bending is listed, you can compare this to the bending stress you calculated.
dieseljohn said:
This is not exactly an easy thing to calculate I'm afraid. Someone with access to and the skill to use an FEA package might be able to do it.
FWIW I would guess that the BS for glass table would be for it not to break if a person fell onto it. If this is the case, it will support your 50lb telly no problem.
You could put a 50lb weight on it and see what happens, if it doesnt break straight away it porbably never will.
Yes, it's hard to calculate as it's a distributed load on a 2-D surface. But you might get some rough idea calculating the biggest moment exerted by the TV (weight acting through center of gravity) at the longest perpendicular distance from the legs, and that might give an idea of the greatest stress the TV can exert on the glass.
distributed loads are much easier on materials than concentrated loads. You know, my refridgerator has glass shelves that aren't that thick, but they hold a lot. If your glass is pretty thick and tempered, it will probably be fine.Thanks for your replies.
Not planning any hanky panky on my table top thank you Mr Alexp. Wouldn't want to get glass splinters up me conundrums if it broke!
Interesting that this is difficult to calculate. Looking on Google I found a figure of 0.5kN/m2 which I think is about 100lbs/m2. Presumably if you have an area of around 3/4m2 (as this is) you could have 4/3 times that which is about 133lbs.
Either just answered my own question or my TVs gone bump big time (yes I did actually put it on the table this morning before going to work because I couldn't wait to see how it looked).
Not planning any hanky panky on my table top thank you Mr Alexp. Wouldn't want to get glass splinters up me conundrums if it broke!
Interesting that this is difficult to calculate. Looking on Google I found a figure of 0.5kN/m2 which I think is about 100lbs/m2. Presumably if you have an area of around 3/4m2 (as this is) you could have 4/3 times that which is about 133lbs.
Either just answered my own question or my TVs gone bump big time (yes I did actually put it on the table this morning before going to work because I couldn't wait to see how it looked).
It wont take it, not safely anyway, even if it will go on there without actually giving way.
Bare minimum for that, based on the surface area would be 10mm toughened, laminated wouldnt be any better as the two thinner bonded sheets crack more easily.
(I just asked a colleague who knows, I work in the industry)
Bare minimum for that, based on the surface area would be 10mm toughened, laminated wouldnt be any better as the two thinner bonded sheets crack more easily.
(I just asked a colleague who knows, I work in the industry)
It depends a fair bit on where the support is, if you look at the piccy of the girl and where the mountings are, that would probably take it. Although I reckon that the glass in the piccy there is about 10mm anyway. I think the risk is with the support being at the corners.
I could get my colleague to come up with the specifics if he's not too busy. The earlier answer was just an off the cuff gut response, but he's probably right, he's been doing commercial glass loading calculations for decades. If you want a high tech glass building, he's da man.
I could get my colleague to come up with the specifics if he's not too busy. The earlier answer was just an off the cuff gut response, but he's probably right, he's been doing commercial glass loading calculations for decades. If you want a high tech glass building, he's da man.
This is what you need plus the flexural strength of the type of glass you're using. Use a safety factor of at least four. The supports are important but so is the distance between the feet on the bottom of the tv. If, for the sake of argument, the feet were pitched at exactly the same span as the table top supports you could put any load you like on it until the legs of the table collapse. The real world is somewhere in between of course. I spent a few years doing stress calcs on pallets for warehouses and these are similar. It's been too long now, though, for more than a general comment.
motco is correct. The greater the distance between the loading points (points of contact by the TV) and the supports, the greater the moment exerted on the glass, therefore the greater the bending stress. Of course, directly over the legs is a distance of zero, so no load in bending.
It was shown on Grand Designs that Kevin McCloud could stand on a sheet of toughened glass and it flexed but stayed in one piece. As long as the load is evenly spread it can take many times more weight than ordinary glass. The load points are important as previously mentioned. The more distance between supports and load points, the more stress you apply.
Laminated glass made from toughened glass increases this loading even further. It also give a safety factor that if it did break, the glass would hold together without being dangerous.
Stunt men use toughened glass when they do back falls into tables, windows, etc with stress points added. Once they hit it with their body weight, the stress points shatter the glass safely but with great dramatic effect. There isn't the same effect with sugar glass and even this can cut.
Laminated glass made from toughened glass increases this loading even further. It also give a safety factor that if it did break, the glass would hold together without being dangerous.
Stunt men use toughened glass when they do back falls into tables, windows, etc with stress points added. Once they hit it with their body weight, the stress points shatter the glass safely but with great dramatic effect. There isn't the same effect with sugar glass and even this can cut.
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