Worried that your stand won't hold up?

Pharaoh

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I was doing a little number crunching on stand design and interesting topic came up. Exactly how much weight will a 2x4 stand hold?

I know most of us DIY people like to build things so that they could hold four tanks, but I thought it would be nice to actually put down some real numbers and see what we come up with.

Wood selection:

Now, to set the basis for this, you would have to make an assumption about the type of wood that most persons' 2x4 would be made from. After a little research, you will soon find that the most common form of wood that is used for construction lumber is pine. From there, I pulled a little data regarding the tensile strength of various woods. (Seen here)

For this discussion, I decided to go with the norm, pine. I also chose to use the weakest pine available, which would be eastern white pine. Now, eastern white pine, which will further be referred to as just pine, has a parallel compression rate of 4,800 psi. This is the weight that is placed upon the wood when it is used for vertical support of an aquarium stand. The perpendicular compression strength is much lower, at 440 psi. We will address this a bit later as to how it would apply.

The design behind the 2x4 stand:

There is one common design for an aquarium stand that is commonly used. I have attached the drawing below. In my opinion, this stand has a couple extra 2x4s in the design, but as stated before, we DIY people like to overbuild things. I will say however, that the green vertical 2x4s are not needed. The purple 2x4s will be more than adequate to support your tank. I recommend saving yourself a couple bucks and removing these from the design.

As you can see by the drawing, the vertical 2x4s support the weight of the tank as it is distributed across the frame. These vertical 2x4s (colored purple) will be the load bearing parts of the stand. They are also the weakest link in the design. In saying this, these vertical supports will be addressed in relation to the ability of a stand to hold weight.

In the design pictured below, there are eight vertical 2x4s. Depending on your stand, you may have more or less in relation to the size and length of your tank. But for those instances, we can simply change a few numbers to evaluate your stand individually.

Credit where credit is due: Pic below came from reefcentral where the design is explained in detail. Found here.

Facts for the discussion:

-The parallel compression rate of a 2x4 -- 4,800 psi
-The rough end measurements of a 2x4 -- 1.5" x 3.5"
-Number of 2x4 in the pictured stand -- 8

The Math behind the discussion:

The Parallel capacity:

First, we take the end measurements of the 2x4 and figure the contact area. This is

1.5 * 3.5 = 5.25

This gives us 5.25 square inches of contact are per 2x4.

Second, we figure the total area that will be in contact. Remember that we have eight 2x4s supporting the frame of the tank. So, we multiply the number of 2x4s by the end area of a single 2x4.

8 * 5.25 = 42.

We have 42 square inches of contact area.

Third, we bring in the compression rate of the 2x4s in relation to the number of square inches of contact area.

42 * 4,800 = 201,600.

This tells us that the stand in question will vertically support 201,600lbs, assuming all other factors remain constant.

The Perpendicular capacity:

Now you need to look at the Parallel compression of a 2x4, remembering from above, the compression strength was 440 psi. We will assume that you are still supporting this two frames in eight different locations. This will divide the load among each of those supports.

So we bring back the surface area

8 x 5.25 = 42

Then we multiply by the compression strength.

42 x 440 = 18,480 lbs

This tells us that the tank will support up to 18,480 lbs spread across the frame supported by the 8 vertical legs. This could theoretically increase quickly with the addition of more vertical supports.


The verdict:

So our final answer comes to 18,480lbs as the perpendicular compression strength will be our limiting factor. As we all know, that is a lot of weight. This would be the equivalent of about 2,200 gallons of water. Right about this time I am going to throw in my disclaimer. I do not recommend pushing the load capacity of a 2x4 to its limit, but it is important to know where you stand in regard to structural support. I personally feel more comfortable using a 1/4 factor when calculating. The would reduce the load capacity to 25% of the rated value. This is what some would refer to as a bit of a safety factor when designing your stand. Let's see where that puts us in regard to our stand by figuring one of two ways;

42 * (440/4) = 4,620

or

18,480 / 4 = 4,620

I think this is a reasonable number that will keep us far inside the safety limits of a 2x4. In any case, you would be hard pressed to design an aquarium that would actually reach this stress limit. I would venture to say that is would have to be somewhere in the neighborhood of 48 x 48 x 48. Now, lets keep in mind that a tank of this size would need additional vertical supports in order to support the horizontal frame, thus increasing the load capacity.


***I just typed this on a whim, so if you have questions or would like to continue the discussion, please feel free to post away!***

148629DIY_Stand_Template.jpg
 

muskymayhem

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Nov 19, 2009
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Pharaoh;3817739; said:
The parallel compression strength is much higher, so there won't be a need to address it in this analysis as it will not be the weak link in the chain.
Correct me if I'm missing something, but doesn't the compression strength only cover where the red 2bys in your sketch are sitting on top of the uprights and being compressed between those uprights and the tank. I don't think it covers the span between the uprights. In various building projects I have completed, I have never really been worried about the compression of the uprights or the horizontals, but the span of the horizontals between the uprights. With a tank sitting on top I don't want any stress on the tank caused by deflection across the span.
 

Bderick67

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I would keep the green 2x4s just for the ease of fastening.
 

muskymayhem

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Pharaoh;3817739; said:
Now, lets keep in mind that a tank of this size would nee additional vertical supports in order to support the horizontal frame, thus increasing the load capacity.
Forget my first post. Of course as soon as I posted I noticed the above basically covering what I said and being such a noob I can't edit my last post.
 

Pharaoh

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muskymayhem;3818029; said:
Correct me if I'm missing something, but doesn't the compression strength only cover where the red 2bys in your sketch are sitting on top of the uprights and being compressed between those uprights and the tank. I don't think it covers the span between the uprights. In various building projects I have completed, I have never really been worried about the compression of the uprights or the horizontals, but the span of the horizontals between the uprights. With a tank sitting on top I don't want any stress on the tank caused by deflection across the span.
In this instance, I was referring to the parallel compression strength of the 2x4s which were in between the vertical supports and the tank. This is much higher that perpendicular compression strength.

What you are referring to would go into a different section of calculation. I believe for this, you would want to calculate the modulus of elasticity and then figure how far the 2x4 would bow when weight is applied.

I do caution that this may not necessarily be that important. Keep in mind that most plastic trimmed tanks can easily be supported on the corners with no support along the span at all. This has been shown with numerous tanks set on cinder blocks.

I like to ensure that there are no spans over 24-30" that do not have support. You really do not want to put the design in the position to where the frame will be supporting at all. The purpose of the frame is to distribute the weight.
 

Pharaoh

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Bderick67;3818038; said:
I would keep the green 2x4s just for the ease of fastening.
They wouldn't be a bad idea if you don't have specialty tools. I guess I tend to forget that at times. I recommend a Kreg Jig to anyone that works with wood on a consistent basis.
 
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john73738

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Nov 8, 2009
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Thanks Pharaoh, I was designing my tank stand in my head as I was driving home from work just a couple minutes ago. That is very facinating information, and validated that my idea will not only hold 2 tanks but my car also :)

Bear
 

big dovii

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Umm correct me if I'm wrong, but can a 2x4 not hold much more downwards force than that? My dad is an engineer and seems to think so.
 

Pharaoh

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big dovii;3818306; said:
Umm correct me if I'm wrong, but can a 2x4 not hold much more downwards force than that? My dad is an engineer and seems to think so.
From what I have researched there are many other types of wood available that would hold a LOT more than eastern white pine. I chose this particular pine as it is a fairly commonly acquired type of wood and the eastern white pine is the weakest on the list. You could do hundreds of different examples and they would be all over the charts in strength
 
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