calculating load limits of wooden shelves


I am going to build some oak shelves and would like to know how to calculate maximum allowable load. The size approximately 15" deep by 45" wide, thickness 3/4". Thanks.
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Bruce T wrote:

15 * 45 * 10 / 0.75 = 9000
9000 pounds?
One of us is missing something here.
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Span is the important issue here that is missing. If you add a center support in the shelf, you can assume that the span is halved and more than double the load.
9000 lbs is wrong.
My framing book offers the following advise...for 3/4 inch plywood with 48 inch spacing between supports plan for a load of 40 lbs per square foot.
Now there are several issues with this.
1) this assumes the load is live, not dead. 2) It assumes that the supports are down both sides 3) It assumes that the support offers a resting area of at least 1 inch on each side 4) It does not assume a constant load
You will see some sag in the shelf boards on a constant load over a long period of time.
A shelf tab in the center back of the shelf will help a lot.
Doug

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wrote:

Also, something else I've done in the past is to glue a strip into a dado which is located not far from the front edge of the shelf. Also, I further assume that the rear edge of the shelf is fixed to the back (plywood or somesuch) and the ends are themselves located in dados. That'll hold up pretty well.
However, the look of the shelf is definitely affected by adding that strip. It might not be acceptable for his design.
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Joe Barta wrote:

Certainly is. the standard load is not 10 per square inch. That's higher than the load for a floor. Shelves would be more like 10-20 pounds per linear foot.
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207.115.17.102:

Assuming the rest of the calc is true it should be multiply by 0.75 not divide?
this is useful; http://www.woodworkersweb.com/sagulator.htm
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