Second Floor Fish tanks – beam loading for the non-engineer

This is a question I see come up a lot and I haven’t seen a good answer yet. Also, articles I have read on the internet seem to be geared for another engineer. So, I am going to try to give an reasonable explanation for people who passed high school math. Also, from the questions and comments, I might rewrite a little of the article.

The first assumption is going to be that the building is built to modern American building codes. These were implemented in about the 1920’s and modern codes haven’t changed much since the 1950s. (40lbf/ft2 room load, 16” on center framing, etc)

Modern rooms are designed to withstand a force of 40lbs per square foot. This is a confusing notion because you can safely place an aquarium that has a floor pressure of more than 40 lbs/ft2. This standard means that you can place 40lbs/ft2 everywhere in the room and still be safe. This is a matter of how to safely load a beam.

So, let’s imagine that we did place steel plates that are 1’X1’ and weigh 40 lbs everywhere in a room. We will use a room that is 8’X16’ for an example. This is a safe room load.




Now, we can re-stack these plates and redistribute the load. This is simplified representation of the plates. This is also a safe room load.






Things can be moved around again. This is also a safe room load.






But don’t do this. This is an unsafe room load.






As you can see in the examples, it you take the beam length and multiply it by 40lbs/ft2, you get the total load that a beam can withstand. The longer a beam the more weight it can hold because it is thicker.

Find your fish tank weight
Water is 8.33lbs/gal. A safe assumption to include the stand, filtration, rocks, and the water in filtration is use 10lbs/gal. Then add the dry tank weight.

Full Tank weight=10lbs/gal + Dry tank weight


Now, you can see if the tank can be placed safely using the 40lbs/ft2 stacked load concept. Let’s use a 125 gallon glass tank (200 lbs dry weight) for an example in our room. Also, the stand will be 18” wide and 6’ long.

Full Tank Weight = (125 * 10) + 200 = 1450lbs
Since we are concerned about weight per linear foot
(Total weight)/(stand length) ---- 1450/6 = 241 lbs per linear foot
We could have calculated the pounds per square foot, but we used the same stacking principal as we did with the steel tiles in example 1.

Now, let’s put it into our room. And see what we get.







Since 241 lbs/ft2 per beam is less than our 320lbs/ft2 per beam this is a safe room load.

Summary:
Calculate the safe beam load ---- Beam length * 40lbf
Calculate the aquarium weight --- 10lbs * #gallons + dry tank weight
Calculate the lbs per linear foot of the stand ---- full aquarium / stand length
Make sure the lbs per linear foot of the full aquarium don’t exceed the safe beam load

Assumptions: The room is up to modern building codes, the beam direction is known


A note about approaching safe loads and exceeding safe loads.
1) If you pass the safe load by a small amount, (less than 10%) you might not be past the safety factor and the situation might be OK.

2) If you pass the safe load by 25%-50% this shouldn’t produce catastrophic results, but probably will cause sag over time. This is not only bad for the building, but can cause a glass tank to crack,

3) If you pass the safe load by 100% or more (i.e.: putting the tank parallel to the beams) you are asking for catastrophic failure during filling.

A final thought. You might have a couch or other furniture in the room that needs to be taken into account as well. People don’t count because they are considered a dynamic load and not a dead load.

Most large lumber yards (ones that sell trusses and engineered lumber) have somebody who can help with this problem.

There have been cases where people have put extra joists and columns in their basement to hold the load. If you do this, place a column under each corner of the tank and put one or 2 extra joists under the tank edges. Also, it helps to lag screw the extra joists to the existing framing. Putting in an extra joist that spans from load bearing wall to load bearing wall can double the load that that particular area can hold. This makes sense; a doubled joist can hold double the weight. Also, there are engineered laminates that can hold more than 40lbs/ft2.

Bderick67;2080796; said:

Nice work on this.

Click to expand...

Thanks. Also, this is an oversimplified take on beam loading. Actually there are conditions to load a beam past the "stacked plate concept" load equivalent. These concepts take up first half of a statics for engineers text book. That involves known load conditions, not general loading, then actually calculating the stress at each potential failure point in the beam. A lumber store and most engineers will not put a stamp of approval on this kind of calculation. Also, the placement equivalent of each load isn't exactly correct either for further engineering calculations. So if a future engineer is trying to learn something off of this explanation I just want to make that clear.

If anybody needs further explanation or a real example worked let me know. Also, if you would like myths like fat uncles jumping off of couches to test the room load I can dispel that as well.

It is mostly correct. I certainly wouldn't consider it an article for a non-engineer or at least for somebody who wasn't an engineering student. Also, there really wasn't a clear explanation on how to calculate a safe load and some things were over complicated. I really don't think we need to calculate the buoyancy force of our tank decorations to get an accurate weight.

Also, like most engineers, he was very general and would like to consider the individual situation before giving a clear answer.


I somewhat disagree with this;

So, the best practical position is often as close to a bearing wall as possible. That way the aquarium weight is distributed to as many floor joists as possible. And the closer to the wall the aquarium can be positioned the more total weight in pounds the floor joists can support.

Number 2 pine joists can cause problems with a huge normal load(crushing load). The know inclusions can cause issues. But, who is going to put their aquarium in the middle of the room? So, the point is kind of moot.

A lot of structural engineers lack the extensive material science background for certain situations.

On the other hand, he would probably say my explanation is a bit too broad.

Here is my second floor tank in my old house. I put in extra floor joists since it ran parallel with the current joists. I had to cut the floor up and drop in the beams since the basement was finished. On the up side, I was able to run direct plumbing for drain and fill.

It looks like this is cycling pre-fish. Also, I later put in a new floor and canopy.