Shelving loads

[poolhound]

I am doing some re-org in my shop and trying to fit in some more lumber that is currently stored elsewhere. I have some shelving bracket systems similar to the link below (think it came from home depot) and am trying to figure out the safe loading factors.

http://www.rubbermaid.com/rubbermaid...d=HPProd100450

for example this bracket says 225lb per pair so if i have 3 supports can I support 3371bs or 4501bs for 4? Is it really that simple?

Also does anybody have a rule of thumb to figure out the weight of boards based on bd/ft. I know each species has a different density and the weight will also depend on moisture content but If I came up with a conservative factor for say dense HW, light HW and softwoods and could figure out the equation then I could make sure I dont overload the shelves.

[poolhound]

OK, I just answered my last question with a quick google search, I guess I should have done that first.

http://www.woodweb.com/cgi-bin/calcu...r=weight_bd_ft

http://www.csgnetwork.com/lumberweight.html

http://www.timberbuyer.net/weight.htm

[pelligrini]

I don't really have any specific answers for you, but I used a similar bracket from Lowes in my storage addition.

I just located the vertical bars 24" OC to correspond to the studs I was screwing them into. I did find out that the vertical supports don't take impact loads very well. After I had all the brackets in and loaded I was moving my plywood in on the other side. Two pieces of 3/4" PT fell over and bent down a couple shelf brackets. Actually the brackets were fine, the support bent in.

[poolhound]

I don't really have any specific answers for you, but I used a similar bracket from Lowes in my storage addition.

I just located the vertical bars 24" OC to correspond to the studs I was screwing them into. I did find out that the vertical supports don't take impact loads very well. After I had all the brackets in and loaded I was moving my plywood in on the other side. Two pieces of 3/4" PT fell over and bent down a couple shelf brackets. Actually the brackets were fine, the support bent in.

I cant quite tell from the photo but are they approx 8' bds and do you have 3 or 4 supports?

[pelligrini]

Most of the boards are 8' some 10'. There would be 3 supports for the 8' lengths. I hang the stock off the ends of the brackets 1'.

I lost a little space going with more rows of shelves, but I find it easier to locate and access materials in smaller stacks. The bad thing about these types of brackets is the height of them. You end up using about 2-1/2" per row instead of the 3/4" or 1" thickness I've seen on higher end packages or DIY pipe supports.

[poolhound]

I just did this little calulator in excel but the formatting appears to get lost, I will try and find another way to post it. Either way based on these conservative figures you can see that with only 3 100lb capacity brackets you can get 60 bd/ft of dense HW which would be 15 board based on an 8'x6"x4/4 bd. with 4 brackets that goes up to 80 bd/ft or 20 boards. I dont think I would load them this much but it should provide plenty.

lbs/bdFt
Dense HW 5
Medium HW 4
Light wood 3

Bracket load 100 lbs
Average bd/ft 4 4/4 x 6" x 8' = 4 bd/ft

Bd/ft load/shelf
Brackets Dense Medium Light
3 60 75 100
4 80 100 133

Boards/shelf
Brackets Dense Medium Light
3 15 19 25
4 20 25 33

[LCHIEN]

PH,
I generally use about 60 lbs per cu ft which is the upper middle of the wood density and covers most of the woods you are likely to be using and have a lot of.
Since 1 bd-ft is 1/12th of a cu ft, then about 5 lbs per board foot is reasonable.
For shelf loading its easier for me to use cu feet, for example a 1 ft shelf standard, with 6 foot long boards stacked 8-inches high would be 1 x 6 x 2/3 or 4 cu ft. which would weigh about 240 lbs.

About shelf brackets loads, don't forget that these are usually quoted with the weight spread evenly over the length of the bracket.
Hanging all the weight on the end will break the bracket, placing all the load on the inside few inches will allow it to withstand much more load.
the force on the bracket is actually the sum of the point loads at any point times the distance from the wall. That's why brackets are usually tapered towards the tip and thicker near the wall, the stresses there are much higher due to the loads on the end.

Also, using more than two brackets, load sharing will depend upon how well they are lined up. If you line the up perfectly and the boards are infinately stiff, then they will share the load equally. If the boards are infinately stiff, but you have the center bracket too low then the end brackets will each carry half the load. In real life boards bend and brackets give, so small misalignments will tend to equalize as the boards sag and the highest/most loaded bracket gives a little. Still it's important to get the brackets lined up as best you can.

[LarryG]

for example this bracket says 225lb per pair so if i have 3 supports can I support 3371bs or 4501bs for 4? Is it really that simple?

Well, I've always operated under the assumption that it really is that simple. I'm not an engineer but I cannot imagine how it would be otherwise. The main assumption would be that the load is evenly distributed, but with lumber as the load that is more or less a given.

In my experience, however, the means of attachment to the supporting substrate, and/or the substate itself, is usually the limiting factor. Even if the individual brackets or the standards they snap into are technically not overloaded, you may have problems keeping the whole works on the wall. I've had the worst luck with loads attached to a wall covered in gypsum board, which will often wallow out around the fasteners holding the standards to the studs behind. Attaching directly to the studs themselves, or to a solid substrate like plywood or shiplap siding, is much better.

Another trick that helps a lot is to run a piece of wood down the face of the wall from the bottom of the standard to the floor. This helps prevent the standard from slowly creeping down the wall when a heavy load is applied.

[jking]

Well, I've always operated under the assumption that it really is that simple. I'm not an engineer but I cannot imagine how it would be otherwise. The main assumption would be that the load is evenly distributed, but with lumber as the load that is more or less a given.

If the boards extend past the last bracket around 1/3 to 1/2 the distance between brackets, your assumption would be fine. If, however, nothing extends past the last bracket much at all, it doesn't hold true. For example, if you have three brackets four feet apart, you'd want to extend your shelving around 18" - 24" past. If you stopped the shelving at the last bracket, the middle bracket could end up carrying significantly more load than the two on the ends.

It comes down to understanding what "evenly distributed" entails. I would suspect many in the WW community would do it right based on a gut feel or experience.

[poolhound]

PH,
I generally use about 60 lbs per cu ft which is the upper middle of the wood density and covers most of the woods you are likely to be using and have a lot of.
Since 1 bd-ft is 1/12th of a cu ft, then about 5 lbs per board foot is reasonable.
For shelf loading its easier for me to use cu feet, for example a 1 ft shelf standard, with 6 foot long boards stacked 8-inches high would be 1 x 6 x 2/3 or 4 cu ft. which would weigh about 240 lbs.

I like the lb/cu ft approach, it seems to make sense. If I keep widths to 12" and dont stack more than 6" high (much higher and its a PITA to get stuff of the bottom) then I end up with approx 30lbs per linear foot. Thats pretty easy to remember. So 10ft bds would be 300 lbs etc etc...

[cabinetman]

If the boards extend past the last bracket around 1/3 to 1/2 the distance between brackets, your assumption would be fine. If, however, nothing extends past the last bracket much at all, it doesn't hold true. For example, if you have three brackets four feet apart, you'd want to extend your shelving around 18" - 24" past. If you stopped the shelving at the last bracket, the middle bracket could end up carrying significantly more load than the two on the ends.

It comes down to understanding what "evenly distributed" entails. I would suspect many in the WW community would do it right based on a gut feel or experience.

You make an excellent point. It would be interesting to know how the weight per bracket was determined.
.

[JimD]

I agree with cabinetman. Getting a number without understanding the basis is not real valuable. If it is the failure point of the bracket, I would cut it in half for a normal working load. If a factor of conservatism of 2 was already applied, however, then it could be appropriate to load to this level but I would fasten them securely to something that will take that much load. Failure will occur at the weakest point. That might not be the bracket.

Jim

[pecker]

Be sure to use something beefier than drywall screws to hold the standards to the studs. The screw heads will snap off before the brackets fail.