Glass shelf design strength 1

[pizza]

Hi.
I am designing a glass shelf that is made of 3/4" thk tempered glass and is 23" wide by 26" deep (front edge to back edge). This shelf is supported on the sides of the shelf only at the very rear by 4 clamping type shelf brackets, 2 per side. The center to center distance between the clamps is 5 1/2 inches. This shelf will need to support a weight of 35 lbs centered on this shelf and 8 from the front edge of the shelf.

How do I analyze whether this shelf will be adequately strong to hold this weight? How do I break this problem down to confidently say that this shelf is strong enough to support this weight?

See my attached pdf file.

Thanks to all in advance

 

[Compositepro]

My "guess" would be that the shelf is strong enough for the weight but I would be far more concerned with someone leaning on the shelf. This makes the 35 lb. question irrelevant. The question should be what should the design load be.

 

[pizza]

The 35 lb question is still relevant. No one will be leaning on this. This is a worst case scenario.

 

[dik]

The manner of support will put fairly high concentration of load at the front 'side brackets' and the stresses will vary depending on the 'hardness' of these supports. I haven't run any numbers through, but the proportions are in the ballpark.

Dik

 

[Lion06]

Do an FEA of the glass to get a maximum stress, then keep it under the allowable per ASTM E1300. I think it's somewhere in the neighborhood of 10.6 ksi for tempered glass. Also note that there are reduction factors if this is laminated glass and it's a long term load.

 

[pizza]

Thanks.

Unfortunately, I'm not versed in FEA nor do I have access to an FEA program.

Are there any on-line FEA free programs that I could learn and use appropriately out there on the Web?

 

[lumenharold]

FEA is a Garbage In - Garbage out process. We defer to an expert when needed even though we have a "lite" version of COSMOS built into SolidWorks. If it is not your area of expertise and you want to reduce your liability, my two cents would be to outsource the FEA.

Free on-line programs are nice but are not always accurate. If you are not familiar with FEA, how would you know if it were wrong?

Again, just my opinion.

Harold
SW2009 SP4.0 OPW2009 SP2 Win XP Pro 2002 SP3
Dell 690, Xeon 5160 @3.00GHz, 3.25GB RAM
nVidia Quadro FX4600

http://www.lumenflow.com

 

[jedward]

glass is a very strong material but its failure occurs in tension at typical values of 1000 to 3000 PSI

the primary concern is to avoid putting the glass in tension AND to provide "soft" supportng boundary conditions
no contact with hard materials
soft in this context can be typical "hard" plastics
eliminate sharp corners for materials contacting the glass to distribute the local loads
design appears very robust

 

[pizza]

To lumenharold,

Exactly why I included the word "appropriately" .

Thanks so much for the advice. I have always known that FEA is not some CAD - like program that anyone without training or engineering education could just use willy nilly.

I understand where you are coming from.

Thanks