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Typical design stress vs. Allowable bending stress

Typical design stress vs. Allowable bending stress

(OP)
I am designing a 1/2" thick x 3'-0" wide soda-lime-silica float glass to span over 4'-0" OC (3 span, typical). The manufacturer has provided me with typical design stress for 0.8% probability of breakage, typical mean modulus of rupture and other bunch of properties. However, there is no allowable bending stress provided. What is the relation of typical design stress vs. allowable bending stress? How can I check that 1/2" thick glass as mentioned above can span 4'-0" OC for 40 PSF total load (DL+LL)?

RE: Typical design stress vs. Allowable bending stress

When I design glass, I use ASTM E-1300.  There are guidelines in there for annealed, heat-strengthened, and tempered glass with allowable stresses for each.  I typically do a pretty detailed finite element analysis with plates to get the maximum bending stress and compare that to the allowable out of ASTM E-1300.

RE: Typical design stress vs. Allowable bending stress

What is it being used for??  If highly critical I might use a 4 or 5:1 SF vs ultimate.  Bolts are usually in this range.  If it is just for looks, 2 or 2.5 might be OK.

RE: Typical design stress vs. Allowable bending stress

Follow some guide. If you are on the optimistic, industry side, look for the Glass Handbook (McGraw Hill) .. I don't find it now, my books seems to be developing legs.

Look for the program MEPLA,  a FEM program for glass, for more conservative values.  

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