Wood shelf "Sag-ulator"

[ebinmaine 67,394]

I find it interesting when I trip over tools used in other industries and/or hobbies that are likely commonplace to many folks but not even a speck on my radar screen. 

 

First people I thought of here were  @953 nut and @8ntruck  and I'm sure more than a few of you have seen this. 

 

 

A wood shelf Sag Calculator. 

 

Very interesting.  

 

I found it while looking at ways to mount medium duty shelves in the new workshop space. This is a Pole Barn so the support structure available to me is 96" on center. 

I don't want to go buy more lumber so I was wondering how and what I could attach at that spread distance using the 3/4 pine we have on hand. 

Turns out with a 2 layer sandwich glued and screwed and good end attachment I'd be fine with 100 lb capacity of spread weight per 8 foot section. More than adequate.  

 

 

 

https://woodbin.com/calcs/sagulator/

 

 

 

[JPWH 6,033]

You could greatly increase the capacity by screwing and gluing a board vertical under your shelf. Be sure to have crown up. 

[ebinmaine 67,394]

3 minutes ago, JPWH said:

You could greatly increase the capacity by screwing and gluing a board vertical under your shelf. Be sure to have crown up. 

 

Couple good points there. 

 

Another thing I learned recently.  Going by Code in most areas  (Maybe national now?)  A 2 x 4 or 4 x 4 can no longer be used horizontally as a supporting piece,  think floor joist. 

If a horizontal brace of 4" or less is desired/ required it needs to be made of a piece of 2 x 8 sliced in half. 

 

I'm considering using a piece like that, to be added later. 

 

[953 nut 55,157]

I had never heard of a Sagulator before.            I have been a dumpster-diver all my life and proud of it.  Old bed frame angle irons screwed/bolted to the underside of a shelf will add a lot of rigidity.  Another thing I've done is attach some light-duty chain to the roof rafters/trusses and the edges of shelves.

[ri702bill 8,311]

20 minutes ago, JPWH said:

You could greatly increase the capacity by screwing and gluing a board vertical under your shelf. Be sure to have crown up. 

Turning a flat beam into a "Tee" shape is an excellent way to increase the beam's load capacity. Basic Engineering...

[ebinmaine 67,394]

10 minutes ago, 953 nut said:

attach some light-duty chain to the roof rafters/trusses and the edges of shelves.

 

Neat idea too. 

 

Because I want to keep the floor space under the shelves free I've thought about doing similar but with a strip of wood. 

I like the chain idea....

 

 

[squonk 41,051]

18 minutes ago, 953 nut said:

I had never heard of a Sagulator before.            I have been a dumpster-diver all my life and proud of it.  Old bed frame angle irons screwed/bolted to the underside of a shelf will add a lot of rigidity.  Another thing I've done is attach some light-duty chain to the roof rafters/trusses and the edges of shelves.

Old bed frames are some of the best angle iron you can get to build stuff out of. The guy who does all of my welding grabs every frame he runs across when folks toss them.

[Racinbob 11,048]

The vertical board under the shelf is a great idea and even better if the vertical board is plywood. I typically use 11 ply 3/4". In extreme cases (I would say yours is just that) I'll laminate two layers together to basically make a "2x4" or "2x3" out of plywood. 

Inside the house we have some various low cost shelving made with the crap particle board. I think that stuff will sag under it's own weight. I'll dado in about 1/2 the thickness of the shelving board and glue in a piece of the 11 ply as wide as I can without compromising the looks. No more sag. 

 

Edited May 12 by Racinbob

[ri702bill 8,311]

One improvement is to use I beam construction - the upper half is in compression, the lower in tension. That almost negates the force.

[ebinmaine 67,394]

27 minutes ago, ri702bill said:

One improvement is to use I beam construction - the upper half is in compression, the lower in tension. That almost negates the force.

 

Torsion box. 

Another neat thing I didn't know about til yesterday! 

[JoeM 7,873]

47 minutes ago, squonk said:

The guy who does all of my welding grabs every frame he runs across when folks toss them

And the price of steel has more than doubled in the last three years. 

 

I bought some material for a project a couple months ago, they should have passed out shots of booz before giving the price. 

[ri702bill 8,311]

4 minutes ago, JoeM said:

And the price of steel has more than doubled in the last three years. 

Right you are. I have to recalculate the cost of materials every time I fab up a set of F plate & side braces for someone....

And the choices of stock sizes seems to be a tad smaller too.

[wh500special 2,168]

1 hour ago, squonk said:

Old bed frames are some of the best angle iron you can get to build stuff out of. The guy who does all of my welding grabs every frame he runs across when folks toss them.

Unless things have changed, the reason bedframe angle is special is because it is made from re-rolled railroad track. It’s hard and strong due to cold working and grain alignment. 
 

Bed frames are under surprisingly high stresses and - despite looking simple and flimsy - have a lot of engineering and analysis poured into them.  The energy pumped into the frame by a couple amorous 400 pounders combined with the need to keep the frame compact and cheap takes a lot of effort. 
 

I have some colleagues who came from the bedframe industry…it’s another one of those industries that produces an astounding quantity of product on the order of tens of thousands of frames every day. 
 

Steve 

[wh500special 2,168]

2 hours ago, ebinmaine said:

…

 

 

A wood shelf Sag Calculator. 

 

Very interesting.  

 

… 

 

https://woodbin.com/calcs/sagulator/

 

This is pretty cool.  Bending calculations are fairly straight forward and countless online calculators are available if you know the engineering jargon to use as your search terms.   But this one is neat because it cuts through that overburden and is pre-simplified for shelving.  I’m gonna bookmark this one. 
 

I see they did make note that the shelves will sag more over time (creep).

It’s not a bad idea not to over-stiffen a long span that might get heavily loaded as the sag can serve as a visual reminder to keep the loads reasonable and in bounds with the rest of your structure. 
 

Steve

[lynnmor 7,303]

Keep in mind that your barn may have wide temperature and humidity swings that will affect wooden shelving.  I have particle board shelving that needs to be flipped regularly due to sag.

[ebinmaine 67,394]

4 hours ago, lynnmor said:

Keep in mind that your barn may have wide temperature and humidity swings that will affect wooden shelving.  

 

Yes it does. We've seen the effects just in the first couple years. 

 

 

[8ntruck 6,998]

Yup.  Lots of neat canned programs (apps?) out there.

 

Me?  I would have dug the old statics book out and opened it to the beam deflection section.

[JimSraj 429]

If you can locate and fasten,the shelves on top of the girts it will help support the back of the shelf and add some stiffness along the length. Chain hung from above, mid span, might suffice and it doesn’t take up much space. I have hung 2’ wide metal shelving this way and it works well. 

[953 nut 55,157]

11 hours ago, 8ntruck said:

Yup.  Lots of neat canned programs (apps?) out there.

 

Me?  I would have dug the old statics book out and opened it to the beam deflection section.

Ya,   I've got a text book from my younger days that tells you all about the modulus of elasticity of various materials but it ain't like @ebinmaine is building a skyscraper.

[ebinmaine 67,394]

21 minutes ago, 953 nut said:

Ya,   I've got a text book from my younger days that tells you all about the modulus of elasticity of various materials but it ain't like @ebinmaine is building a skyscraper.

 

 

Well not yet anyway

[formariz 11,987]

On 5/12/2024 at 7:17 AM, ebinmaine said:

Turns out with a 2 layer sandwich glued and screwed and good end attachment I'd be fine with 100 lb capacity of spread weight per 8 foot section. More than adequate.  

It will not be adequate . May not break but it will sag considerably. That is a fact. If it sags enough it will at the very least compromise the attachments at the ends. 
I have built miles and miles of shelving over my career and can tell you for a fact that anything out of any wood related of 1-1/2” in an eight foot span will sag to the point that in the very least its unsightly and unprofessional.

There are many things one can do to make it work even with a 3/4” shelf some of which were already mentioned. Laugh if you want but the photos below is what I always resort to, and in over 40 years I have never had a single failure. I have literally built bridges in this manner. Depending on the situation to be used for, the materials such as the rope or the attachment points may be a steel cable if needed, but the principle is the same. It is adjustable according to the load , or atmospheric conditions (which affect materials )a crown is always the desired condition. The one shown although a little buried you can see is a simple 3/4” mahogany board about 10” wide by 8’long not even attached at the ends. It simply rests on top of ends. Over the years at different times I probably have had  over 300lbs on it, sometimes increasing the tension to maintain a crown. At one time it had four beer kegs full of wine for over one year. 

 

 

Edited May 13 by formariz

[SylvanLakeWH 25,525]

On 5/12/2024 at 10:11 AM, wh500special said:

The energy pumped into the frame by a couple amorous 400 pounders combined with the need to keep the frame compact and cheap takes a lot of effort. 

 

Just... stop... 

 

Please... my eyes... can't feel my eyes... 

 

 

Visuals... again with the visuals... 

 

@ebinmaine your posts tend to bring out the visuals in people... started with your pressurized gas tanks technique if i recall...  

 

oh man... flashback!!! 

 

 

 

[ebinmaine 67,394]

3 hours ago, formariz said:

There are many things one can do to make it work even with a 3/4” shelf some of which were already mentioned. Laugh if you want but the photos below is what I always resort to, and in over 40 years I have never had a single failure. I have literally built bridges in this manner

 

I like that idea quite a lot.  

 

My latest intention was to build the shelves then add a piece of vertical small chain or cable to the midspan of the shelves which would be attached at the ceiling rafters. 

 

The only (but serious)  disadvantage to using the rope/wire under suspension is a lack of space between shelves. I'll have to ponder and measure some more. 

 

[formariz 11,987]

5 minutes ago, ebinmaine said:

The only (but serious)  disadvantage to using the rope/wire under suspension is a lack of space between shelves. I'll have to ponder and measure some more. 

 

True if in fact there are other shelves underneath. For that instead of the shown method, same can be accomplished with 1/4” threaded rod and a turnbuckle in center. (By the way I used that system to straighten large massive pocket doors that were twisted and were only visible on one side. Rods were mounted diagonally along twisted corners. Some of them were 10’ tall by 6’ wide.) That way it stays close to the underside of shelf and has same effect. You only lose the wow factor from the visitors. With the rod from ceiling it should go through all shelves using nuts under each shelf  so you can individually adjust the crown on each one without affecting the others. 

[ebinmaine 67,394]

50 minutes ago, formariz said:

same can be accomplished with 1/4” threaded rod and a turnbuckle in center

How do you attach at the ends?