allowable shear in glass?

[Lion06]

My boss has asked me to check something that resembles block shear in a glass panel. I don't even know where to begin to find allowable strengths for glass. Can anyone point me in the right direction?

 

[concretemasonry]

Are the loads uniformly distributed?

 

[shepherd]

The GANA glazing manual is one thought. I'm not sure if it addresses your particular problem (I switched companies and no longer have it). I know it does have a lot of good glass design info and may be worth a try.

http://www.glasswebsite.com/publications/default.asp

 

[whyun]

Glass unit masonry may be used as non-bearing and non-LFRS application per 2006 IBC Section 2110 or per ACI 530-05 Chapter 7.

If you are talking about glass panes as used in exterior or interior windows, they should not be used to resist any loads other than out of plane wind loads or 5 psf interior load.

 

[JAE]

Glass is very brittle, of course, unless it has embedded reinforcing. The use of [φ] factors in LRFD is based on variability of the nominal strength AND the abruptness of the primary mode of failure.

Glass may be very uniform in thickness and strength (thus implying a high [φ] factor, but very brittle with abrupt failure. Thus [φ] would get very small and thus you would really have very little strength to count on...therefore, whyun is right that only very small loads should be counted on.

Here are a few paragraphs picked up on the net:

Physical Properties
Depending on the composition, some glass will melt at temperatures as low as 500° C (900° F); others melt only at 1,650° C (3,180° F). Tensile strength, normally between 2,745 and 5,500 N/sq cm (4,000 and 8,000 lbwt/sq in), can exceed 68,650 N/sq cm (100,000 lbwt/sq in) if the glass is specially treated. Specific gravity (density relative to water) ranges from 2 to 8, or from less than that of aluminium to more than that of steel. Similarly wide variations occur in optical and electrical properties

Glass does not have any plastic
range. Glass is very strong 5x10^6 lb/in^2 but actual glass products exhibit strengths 500 to 1000 times lower due to surface imperfections and stress concentrations.

Theoretical strength is around 1 million psi, which whiskers approach, while the bulk material is around 5000 psi due to flaws in the glass, which cracks.

Much of what I saw seemed to indicate (and this intuitively feels correct) that the tensile strength depends a LOT on the chemical make-up of the glass itself.

I couldn't find an ASTM test method for glass panes.

 

[Lion06]

It is and interior glass pane. The architect wants it supported on 4 small stainless steel clips. I am supposed to check the "block shear" capacity of the glass for where it bears against the clip due to the 5 psf wind load.
Each clip will see about 50 pounds with an effective shear area (3 sides of a rectangle) of 2.25 in^2.
That is a shear stress of around 20 psi, which I am sure everyone here will tell me is fine, but I need some sort of value that I can actually compare it against for my boss to see.
I've searched the web and even called the glass supplier and haven't been able to come up with anything.

 

[whyun]

Situation you describe warrants a bending capacity of a certain effetive width rather than shear along the three sides of the metal clip.

I'm no glass expert but there may be differences in glass material properties (some more brittle than others? Like different grades of steel).

 

[Lion06]

It is a glass panel 8' wide x 4'-6" high x 3/8" thick (tempered) with 4 clips at the top and 4 clips at the bottom. You think this warrants a bending check? Again, where would I find allowable values to compare against.
Would you normally do this check or leave it to the glass guy?

 

[UcfSE]

Check also forum329 and note that you are cross posting, if you do.