Expert: Roger Zona - 5/15/2011

Question
QUESTION: I live overseas and I'm having difficulty finding an answer to this question. At what types of weight should I start to be concerned for a concrete and rebar constructed building. I am considering putting in a sizable aquarium and I have asked around for the plans for the building but no luck. The only real info I have is that the floor is 6" concrete and rebar. I have a place with a wall directly underneath for added support but at what weight should I start to worry? 40-50PSF is cited a lot for wood construction but wouldn't it be significantly more for this type of building?
Thanks!

ANSWER: Hey Mark,

You are doing the right thing - being assured that the floor will support your aquarium.  A 6" reinforced concrete slab is typical for apartments.  The allowable live load depends on the strength of the concrete, the size and number of reinforcing rods and the span of the slab.  The wall beneath will be of no value unless it is a load bearing wall.

The weight of your tank, when filled with water, must be determined.  Add the weight of the tank itself and then calculate the water weight at approximately 62.5 lbs per square foot.  For example, if the tank is 2'd x 6'w x 3'h, it holds 36 cu. ft.  The weight of the water is 2,250 lbs.  Add for the tank - assume 150 lbs - and the total is 2,400 lbs or 200 lbs per square foot of surface area.

I doubt that your building was designed for that much live load but to be certain, you should contact the governing authority that issued the building permit.  They will have plans on file and the specifications will help you or your structural engineer determine the safety factor and size tank you can support.

I hope this has been helpful.

Roger
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---------- FOLLOW-UP ----------

QUESTION: Thanks for your answer. I have tried to get an,answer but so far no luck. At what weight could I be safe without finding an answer. The tank is custom so I can change to spec. 80, 100? It must be more the 50 for this type of apt!

ANSWER: Hello Mark,

The weight of the floor slab is carried by walls that extend down to a foundation.  I think it would be prudent to get the opinion of a structural engineer.  It sounds as though you are planning a rather large aquarium.  If the size were reduced to 1'd x 5'w x 2'high, the weight would be greatly reduced to 125 lbs per s.f.  This would be much safer.  I also would suggest that you place the aquarium against a supporting wall which distributes about half the weight on to the wall.

Lots of luck,

Roger
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---------- FOLLOW-UP ----------

QUESTION: So if I can keep the total live load of the room under,80psf and the tank itself under125psf I should be pretty safe right? Any heavier than that and I should get some help... sound ok? My original idea was pretty fanned big so ill tome it down to these numbers.

Answer
Hello Mark,

Since you don't know the exact specifications and capacity of the floor system, I would really recommend that you consult a structural engineer.  Reducing the size of the aquarium is a good
idea and you don't want to find out the hard way that your aquarium was too large.    

Good Luck

Roger
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