2x4 Axial Strength

[Tony]

Building a rack for 3 40 breeders. Am planning on stacking them vertically. The rack will consist of 3 2x4 boxes (under the frame of each tank) supported by 5 2x4 legs (2 on each side, 1 running up the center of the back). I am rather certain that the 2x4 legs will be sufficient to carry the load (3 tanks x 40 gallons x 10 #/gal on the conservative side). So basically, we have each 2x4 supporting 240# +/-.

This should be no problem, right? I think I read somewhere that a single 2x4 can carry well over 1000 pounds axially and not break a sweat.

 

[fischfan13]

Tony, I bought all of this a few months back.
This is not my picture, but the picture listed from the person who was selling the set up.
Everything is fine.

 

[Cartel]

I'll try to find the article tonight it's on a reef site that breaks it down more the you ever want to know. The strength of a 2x4 is crazy.

 

[dogofwar]

Charlutz (Charlie) did a presentation on building DIY 2x4 stands (maybe even used 1x4s?). On end, 2x4s are STRONG. They'll warp over time the other way.

Matt

 

[Cartel]

This is the thread I was thinking about. look through it somewhere in there a guy post the ridiculous amount of pressure a 2x4 can take.

http://www.reefcentral.com/forums/showthread.php?s=&threadid=1169964

 

[Tony]

Bill - Nice setup. Looks like they're using 2x4s for posts as well. Does that stand use 2x4s to frame under each tank?

Wil - I saw that post a long time ago and couldn't remember where I saw it. Thanks! Definitely some good reading.

Matt - Wish I could have caught that presentation.

Welp, here's what I came up with:

Here's where it's going in the back of the room. I put it in, but didn't put any tanks on it yet. I'll take more pictures when I get the tanks in.

 

[mrkillie]

Building a rack for 3 40 breeders. Am planning on stacking them vertically. The rack will consist of 3 2x4 boxes (under the frame of each tank) supported by 5 2x4 legs (2 on each side, 1 running up the center of the back). I am rather certain that the 2x4 legs will be sufficient to carry the load (3 tanks x 40 gallons x 10 #/gal on the conservative side). So basically, we have each 2x4 supporting 240# +/-.

This should be no problem, right? I think I read somewhere that a single 2x4 can carry well over 1000 pounds axially and not break a sweat.

With that set-up, your load is approximately 40 psi on the feet of the 2 x 4 (240 lbs /(1.75 x 3.5). Most 2 x 4s are made of pine, which has a vertical compressive strength (parallel to the grain) of 4800 psi (if it's Eastern White Pine), and stronger for most other types of pine. So it looks like you should be fine.

NOT SO FAST MY FRIEND!!!

It is fine if the weight of the tanks is pressing directly down on the wood's end. However, since the center of gravity of the tank will not be directly over the end of the 2 x 4, there will be some component of lateral force (perpendicular to the grain). The lateral compressive strength of pine is only 440 psi. This is why many people will design their stand with 2 x 4s to be constructed with double 2 x 4s. One where the tank shelf rests on top of the inside 2x4, and then the outside 2x4 for added strength and make it look a little better. However, I can tell you that 440 psi lateral strength is plenty good for this set up. Here, the lateral force will be concentrated in the area where the tank shelves connect to the uprights, which comes out to about 20 psi max.

20 psi max vs 440 psi strength - so no problem. NOTE: This assumes that the support posts are on the outside of the shelves. If the supports are on the inside, the pressure is much greater because it will be spread out only over the heads of the bolts or nails that you are using to connect the wood, less than 1 sq. in. ea. On the outside, the pressure is spread over a 3.75" square area where the boards overlap - about 14 sq. in. each.

 

[Tony]

With that set-up, your load is approximately 40 psi on the feet of the 2 x 4 (240 lbs /(1.75 x 3.5). Most 2 x 4s are made of pine, which has a vertical compressive strength (parallel to the grain) of 4800 psi (if it's Eastern White Pine), and stronger for most other types of pine. So it looks like you should be fine.

NOT SO FAST MY FRIEND!!!

It is fine if the weight of the tanks is pressing directly down on the wood's end. However, since the center of gravity of the tank will not be directly over the end of the 2 x 4, there will be some component of lateral force (perpendicular to the grain). The lateral compressive strength of pine is only 440 psi. This is why many people will design their stand with 2 x 4s to be constructed with double 2 x 4s. One where the tank shelf rests on top of the inside 2x4, and then the outside 2x4 for added strength and make it look a little better. However, I can tell you that 440 psi lateral strength is plenty good for this set up. Here, the lateral force will be concentrated in the area where the tank shelves connect to the uprights, which comes out to about 20 psi max.

20 psi max vs 440 psi strength - so no problem. NOTE: This assumes that the support posts are on the outside of the shelves. If the supports are on the inside, the pressure is much greater because it will be spread out only over the heads of the bolts or nails that you are using to connect the wood, less than 1 sq. in. ea. On the outside, the pressure is spread over a 3.75" square area where the boards overlap - about 14 sq. in. each.

Wow, 2x4s are even tougher than I thought. Thanks for the breakdown, Joel. I never really considered the lateral load imposed on the legs, but it makes sense that it exists.

I figured that the weak point in the setup would be the shear connection between the legs and each frame. At each connection, I first tacked the frame in place using nails (so it wouldn't move when I drilled for the lags). I then used a paddle bit to drill holes for 1/2" x 3.5" galvanized lag bolts. From a quick Google search yesterday, I believe these guys are good up to 940# each (!).

 

[Charlutz]

That's exactly it. The weakest point in your support is not the 2x4s, but the fasteners. If the fasteners can support the weight AND the holes you've drilled don't fracture the wood, you'll be fine. Stands have been constructed the way you've done it and held weight (a certain CCA President has a fish room full of racks constructed this way that are older than most of the club members). I use a double set of 2x4's (or 1x3's for smaller tanks) to avoid the fastener issue. I've also notched a vertical 2x4 post to hold the wood (Bill Roberts - Mr. Longstocking ?!? taught me this) and it works quite well and saves on wood.

There are lots of ways to do it. Many will work. The risk is that the ones that don't usually fail spectacularly.

 

[mscichlid]

You should have two bolts or lag screws where the legs attach to the uprights. And because it is narrow from front to back, I would attach the rack to the wall. I would also consider putting a brace or to in the shelves.

 

[Tony]

You should have two bolts or lag screws where the legs attach to the uprights. And because it is narrow from front to back, I would attach the rack to the wall. I would also consider putting a brace or to in the shelves.

Hey Franny,

I did tie it into the wall with a .22-powered nail gun.... It would definitely not be pleasant if it decided to fall forward.

You really think I need two lags at each connection?

 

[Reel Addiction]

Looks good, I like the idea. Im going to use a 2x6 on my front leg so it will be flush with the front 2x4 of each shelf. Then I can skin it with something. With Bills pick I want to put 2 doors that open to the side instead of one that raises. Great thread to use a couple of each ideas.

 

[mscichlid]

You really think I need two lags at each connection?

A well since it's already attached to the wall...

I was told by an architect eons ago to use to bolts or five screws in a star pattern to prevent twisting of the shelves. If I ever find the information, I'll post it.

 

[Tony]

A well since it's already attached to the wall...

I was told by an architect eons ago to use to bolts or five screws in a star pattern to prevent twisting of the shelves. If I ever find the information, I'll post it.

Totally makes sense. Haven't set the tanks up yet. Still have a chance to slip in there and hit each connection with a couple of wood screws. It'll take like 10 minutes... why not?

Thanks again, lady.

 

[Spine]

I'll have to dig up one of my old FAMA magazines and show it to you. It was written by an engineer,he gives you a formula to use. It explains what size wood to use over diffrent lengths and tells you about diffrent failures that can occur and why.

 

[Tony]

I'll have to dig up one of my old FAMA magazines and show it to you. It was written by an engineer,he gives you a formula to use. It explains what size wood to use over diffrent lengths and tells you about diffrent failures that can occur and why.

I'd love to see that, Kev.