Expert: Bruce E. Johnson - 4/17/2009

Question
Hello,

I have a random question for ya...I am buying a 400 gallon fish tank and I would like to place it on the first floor (basement below) but before I do I was concerned with the ability the first floor has to hold what will equal about 4500 lbs. The measurements of the tank will be pretty much 8ft long 3 1/2 feet off the wall. But can the floor support that much weight spread out over that little of space???? I appreciate any help.

Answer
Hi Alison, I need more information.  What are the actual dimensions of the fish tank?  What is the size and spacing of the floor joist?  The closer you put the tank to a bearing wall the more weight the joists will hold.  Obviously putting a big tank out in the middle of the room will cause some stress in unsupported joists.  The closer you get to the wall the more you are placing the weight on the shear value of the joist as opposed to the bending modulus.  Also where did you get the 4500 pound potential weight?  At 62 pounds a cubic foot your tank would have to be 8x3x3 to reach 4500 lbs.  If this is the case then your weight distribution over the floor area would be 4500/24 or 187 lbs a sq. ft...Imagine a 200 pound man standing on one square foot of your floor system will your system hold the weight?  The beauty of water is that it distributes weight evenly over its entire area.  Anyhow getting back to your question, if I knew what size your floor joists are and what the spacing is, I may be able to futher elaborate on this answer..I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com