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Discussion Starter · #1 ·
How much weight can a 10' doug fir 2 x 4 hold if the 2 x 4 is supported at the ends by joist hangers? In other words, the 2 x 4 is laying horizontal like a joist w/ the 4" side vertical.

THANKS!!!
 

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The amount of weight a horizontal element can hold depends on the bending strength of the element (in your case Doug Fir, need the grade), and the distribution of the weight. The worst case in terms of maximum bending stress on the beam comes from a point load at the center of the span. The best case for bending comes from a pair of point loads directly located over the support brackets. A distributed load creates a lower maximum bending stress in the beam than a point load of equal total weight at the center.

Example:

A 10 foot long 2x4 carrying a uniform load of 40 pounds per foot (400 lbs total load) will have a maximum bending moment at the center of the span of 1000 ft-lbs.

The same 10 foot long 2x4 with a point load of 400 lbs at the center will experience a maximum bending moment of 500 ft-lbs.

Whether the beam fails or not is also a function of maximum shear stress, although in most home applications bending moment controls.
 

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Discussion Starter · #3 ·
Thanks for the explanation. I'm trying to plan a storage shelf in my garage.

The garage is 10' wide and I'd like to make the shelf 2' out from the wall. I will put a 2x4 ledger on three sides. The fourth side (running from wall to wall), will have joist hangers holding up a 2x4. Then I was going to connect the two 10' long 2x4's with studs every two feet. Then sheet it with 3/4" plywood.

I'm just trying to determine if I should run a couple supports from the ceiling down to the suspended side of the shelf.

Here is a quick drawing of what I'm trying to do. Do you think this will be strong enough, or do I need supports in the middle?

 

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Interesting, I'd like to hear what Daniel has to say about this.

What are you going to be putting on the shelf?

Is there any reason (clearance underneath) that you can't use a larger 2X in front?
 

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First off, I am in no way an expert. So take this like you'd take helpful advice from some guy just walking past your garage. :)

Without a center support, I think that is going to sag. Just the weight of the shelving will eventually make it sag.

How to avoid this? You could do a diagonal brace below it, a diagonal brace up above it, or you could tie it into the roof with a vertical piece connecting to a ceiling piece that spans at least three of the ceiling joists.

Or you could use a 2x8 for the piece running the span. It depends on how much weight you're going to put on it.

My personal rule of thumb is to never have a 2x4 span more than 4' when it's being laid out up to 24" on center. (A 2x6 is good for 6', a 2x8 for 8', etc.) So by my reckoning, the ideal piece for that would be a 2x10. But that might be overkill if you're just storing Christmas decorations up there.
 

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It looks are you are trying to build a "park-under" shelf at the end of your garage.

Just add another 10' 2x4 to cut the span of the that intermediate 2x4 (that should be elimimated) because it is over-building for a 12" span between joists.

I have built several systems (usually 2 spand in a 24' or 30 wide garage with a post in the middle) in my homes through the years. Usually the rear 2x4 was anchored or attached to the rear wall. The only criticism I get is that they are "ungodly" strong and will attract people in a tornado warning. When I weighed 285#, I got up there and noted it no inkling of deflection. - If your are considering something like a 5.7 liter (350 ci) engine the concentrated weight might be a problem. If it is a 1000 hp Formula 1 engine, it is no problem.

Being supported on three sides, cutting the load on a 10' span by going to 12" spacing and eliminating the 2x4s from front to back makes a waorld of difference. - Fewer 2x4s, fewer hangers and much more rigidity and strength. Just edge nail the 3/4 plywood well, but think I used 1/2" plywood on the first couple.

Dick
 

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What is so sacred about spacing at 16" o.c.? I just used 12" o.c. because it worked for 24" shelf depth (any more depth is really unusable and impractical) to reduce the load on an individual 2x4. Since your are using 3/4" plywood and attach it well it has been proven to be stable. 3/4" plywood properly nailed to a 2x4 provides all the continuity that is needed. - It just a storage area for 20-30 years or until you change your mind and not a prescriptive, no-brain code "life-safety" problem. If you expect to pile up 8' of junk on the shelf, then there could be concern.

I just went out and measured mu present garage and found it was 23' wide (clear) and I used a center post and a 24" long 2x4 beam to spread the load out from the joist in the center of the 24" distance from the back wall to the front 2x4. - The center 10' long 2x4 carries far more load than the back wall (continuously supported" or the front 2x4, but in my case it is spanning about 11' - 6".

Too often, people look at the standard, "no-brain" tables and spans and practices without looking at what is really needed. - Than when you have to do and what is correct and not what is habitual.

I have designed many multi-story buildings and am only risking a dented hood on my two cars IF there is an earthquake, wind, snow and a dynamic load at the same time. - Not a code issue, but a casual use.

Dick
 

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Discussion Starter · #10 ·
Interesting, I'd like to hear what Daniel has to say about this.

What are you going to be putting on the shelf?

Is there any reason (clearance underneath) that you can't use a larger 2X in front?
I'll be storing random boxes of parts to my hotrod project, gallon buckets of paint for the house, christmas ornament, rarely used tools, etc.

The self will be above a garage door, so the larger the beam, the less space I will have available.

First off, I am in no way an expert. So take this like you'd take helpful advice from some guy just walking past your garage. :)

Without a center support, I think that is going to sag. Just the weight of the shelving will eventually make it sag.

How to avoid this? You could do a diagonal brace below it, a diagonal brace up above it, or you could tie it into the roof with a vertical piece connecting to a ceiling piece that spans at least three of the ceiling joists.

Or you could use a 2x8 for the piece running the span. It depends on how much weight you're going to put on it.

My personal rule of thumb is to never have a 2x4 span more than 4' when it's being laid out up to 24" on center. (A 2x6 is good for 6', a 2x8 for 8', etc.) So by my reckoning, the ideal piece for that would be a 2x10. But that might be overkill if you're just storing Christmas decorations up there.
I can't brace the underside since the garage door is under it. I could diagonal brace above. How would you atach the diag. 2x braces to the wall and shelf?

I also may weld up some angle iron 'T' brackets to lag to the cieling joists and screw to the front beam.


It looks are you are trying to build a "park-under" shelf at the end of your garage.

Just add another 10' 2x4 to cut the span of the that intermediate 2x4 (that should be elimimated) because it is over-building for a 12" span between joists.

I have built several systems (usually 2 spand in a 24' or 30 wide garage with a post in the middle) in my homes through the years. Usually the rear 2x4 was anchored or attached to the rear wall. The only criticism I get is that they are "ungodly" strong and will attract people in a tornado warning. When I weighed 285#, I got up there and noted it no inkling of deflection. - If your are considering something like a 5.7 liter (350 ci) engine the concentrated weight might be a problem. If it is a 1000 hp Formula 1 engine, it is no problem.

Being supported on three sides, cutting the load on a 10' span by going to 12" spacing and eliminating the 2x4s from front to back makes a waorld of difference. - Fewer 2x4s, fewer hangers and much more rigidity and strength. Just edge nail the 3/4 plywood well, but think I used 1/2" plywood on the first couple.

Dick
So you're saying I should get rid of the short studs and just run another 10'er down the middle attached to the 2' ledgers?

I hadn't though of that. Hmmmmm...

Might want to consider extending the side 2' 2x's out to 32" to catch the next stud
I'd span the 10' distance too
They will be extended down the sides as well because I plan on extending the shelving down the sides. I just left them off my scetch for simplicity sake. Thanks!! What do you mean you would "span the 10' distance too?" Isn't that what my drawing does? I'm not quite sure I understand you.


Here is a picture of where I'll be building this shelf. I'd like the shelf to be just above the torsion rod. Thanks for all the help guys! I really appreciate it!!!

 

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Depends on the species of wood used, and the grade. A #2, Doug Fir, 1.7, 24"o.c. will span 10' and carry 15# sq.ft. or 150#.
pp #11, table C-1: http://www.awc.org/pdf/STJR_2005.pdf

Dave, 99% of the time, front garage side walls are laid out for the exterior sheathing- from the outside corner, not the inside drywall. You're thinking, though!

Be safe, Gary
 

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if load carrying is a concern and a 45degree bracket is out of the question due to where it would fall, depending on construction using cable at the corners running straight up to the truss would greatly increase the amount of weight you could put on the shelf since the end of your shelf would not be floating out in space anymore.
 

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Do what I did,

I have the exact same application, however i only have 2 walls to support (back and 1 side). I created a 2x4 frame just how you are, 1/2" ply for the decking. I bolted the back and side using lag bolts, and used chain and eyebolts from the front of the frame to the ceiling joists. I spaced this every 4 ft.

I have so much crap on it you wouldnt believe. wheels/tires, tools, x-mas goodies.
 

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Discussion Starter · #14 ·
Thanks for the input guys. I just talked to my dad, who's a carpenter. He suggested using the erector set looking straps they use for garage door installs and dropping a few straps form the ceiling joists grabbing two joists each.

Also, do you folks think it would be better to use short studs like my picture to connect the two joists, or span a middle 10' joist as Dick suggested. Which way is stronger???

Lastly, (stupid question time)- What is difference between kiln dried 2x4s and green studs? What would be best in this application.

Thanks a lot guys!! I'd ask my dad these questions, but he's really busy and I don't want to bother him with my stupid questions.
 

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Discussion Starter · #15 ·
Do any of you folks answer this question for me? Maybe I'm not explaining myself very well.

Would it be better to use short studs like in my sketch to connect the two joists, or span a middle 10' joist instead as Dick suggested. Which way is stronger???
 

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Now that I see your application, I would get three 10' 2x4s. Use one 24" piece on each side if it helps you tie them together. Beyond that, whether you need a center piece going up to a ceiling joist depends on how much weight you're putting up there.

I would not go with short pieces parallel to the long walls, as in your original drawing.

(Then again, I'm a writer, not a carpenter.)
 

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Assume 800,000 PSI for the modulus of elasticity [MOE] for the 2x4 as a worst case, I = 5.4 and y = 3.5/2 = 1.8".
http://www.engineeringtoolbox.com/beam-stress-deflection-d_1312.html
Each short 2x4 will be very strong.
I'd worry more about shearing off the four wall fasteners.

Try it. Cut a 2x4 to length, support it at each end 1/8" above the floor, stand on the center of it on one foot and see if you can see any bending at all at midspan.
You can also use this method to measure the MOE for your particular wood.
 

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The design tables have little real value since this is a unique application and probably not under a code and the design tables do not usually cover shelving for design loads. They might be intersting from an academic standpoint.

The important thing is that is it strong, functional and stable, which could be limited by the connections and the structure it is attached to.
 

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I agree with no short joist and do three the long direction.

If you’re worried about sag use 2x6. Woods cheap right now.

Don’t limit yourself to 24”, find the studs in the wall if you find one at 20-24” great otherwise go to the first stud beyond that.

You’ll end up with a stronger shelf and a little more space.
 

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Concretemasonry, there is a ceiling joist table, on post #11 = 150# total load.

If the short 2x are omitted and the span is 2' ----- it's the same load. To add another 10' 2x4, at 2' span, or 12"on center, you carry the load = 15# per sq.ft. on the middle one and on the rim one = 15# together total 30#. OR 300# total load.

As Ron said, change to one 2x6 in front and 2x ledger with/without the short spacers, total load is 756# or 75# per sq.ft. for Doug fir.

Be safe, Gary
 
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