Subfloor load for Pool Table 3

[TBone2000]

Hi,

First post (be gentle!)...

We will place our pool table (1300 lbs.) on the second floor. Subfloor is Advantech OSB 3/4" T&G with joists 24" OC. Flooring is carpet/pad. We have extra girders in the floor system to provide extra support because we knew we'd have a table on the 2nd floor. The table legs will rest on a portion of subfloor that does not have a joist or girder directly underneath. So the leg might be resting directly between 2 joists.

Now I am beginning to think that the weight of the table, really the pounds per square inch, might be too much for the subfloor panels (not the joists/girders). The area under each leg that makes contact with floor is 28 square inches.

Should I be concerned? Will sagging occur?

 

[boo1]

1300 #= 325#/leg

325#/28 sqin=11.6 psi

the loading is very low
you may have creep in the long run. If that happens just lay two 2x8's under the legs

 

[TBone2000]

Boo1, thanks for the reply and advice...

 

[PEinc]

Sorry, but I don't think boo1 has answered the question. The psi of bearing (compression perpendicular to the wood grain) is not the main concern. The bigger problem is the bending of the 3/4" thick flooring between the joists which are spaced at 24 inches. Also, shear should be checked.

The table leg weight is 1300# / 4 = 325#. To that I would add at least the weight of one person, leaning or sitting on the table, above the leg. Therefore, add maybe another 250#. Therefore, the load per leg could be 575#.

The bending moment is then M ~ PL/4 = 575x24/4 = 3450 in-#. Assuming an allowable bending stress of about Fb = 1500 psi (maybe even a little bit higher), the required section modulus of the flooring is s = M/Fb = 2.3 in^3. The width of 3/4 inch floor required to provide 2.3 in^3 = b = 2.3 x 6 / (0.75 x 0.75) = 24.5 inches. A leg contact area of 28 inches is about 5.3" x 5.3". The table leg weight would need to be distributed across 24.5 inches of flooring. How many floor boards would this require and would the tongue and groove joints be strong enough to transfer the load evenly across several floor board? Twenty-four inches is a fairly large joist spacing and a 575# point load is large for a piece of 3/4 inch think flooring. Is there any sub-flooring to help carry the leg loads? You need to check this out better.

 

[TBone2000]

PEinc, thanks for responding... and yes, my concern is the flexing of the subfloor panels.

My gameroom will have a billiards table and a home theater, and I need carpet and pad for acoustics. Options:

1. Lay a section (9/16" thickness engineered wood flooring) directly under the table, and attached (glued/nailed) directly to the subfloor

2. If #1 fails to meet needs, I could try to position the legs such that they rest directly on top of a joist.

Is #1 viable?

 

[TBone2000]

PEInc:

As a follow-up, I could place circular disks (or squares) under each leg, but on top of the carpet. Each disk would be the same material I specified earlier as 9/16" thick. How large (in square inches) must each disk be to help transfer the load?

 

[PEinc]

Positioning the legs over the joists will not work. Pool tables move all the time. It's only a matter of time before the legs are moved to mid-span between joists. Additionally, you have not checked the ability of the joists to support one or two legs.

Even double layering the floor thickness (3/4" + 9/16") will not help significantly unless the layers are properly glued together or nailed sufficiently to make the layers act as one thicker layer.

Am I correct in assuming that the table is to be disassembled into smaller, lighter pieces in order to get the table to the second floor?

 

[boo1]

I checked the bending and shear in the OSB, using the numbers provided, they were ok. The loading is not significant for typical joists systems. The sheathing is the weak link. Again, i would worry about creep.

 

[TBone2000]

boo1: thanks for rechecking the numbers about creep. From your calculations, will additional wood flooring work as well as the 2x8s you suggested I use?

PEInc: The flooring system (joists) was designed to support the weight of a table/theater. If our floor guy installs wood beneath the table, he always nails it down if the subfloor is wood. Guess I should ask him how far apart the nails are in the wood. And yes, the table is in smaller sections, then brought upstairs and assembled.

PEInc, boo1: are you two using the same methods to calculate ability of floor to support table? I appreciate your help, but your answers are somewhat different (then again, I'm an EE).

 

[PEinc]

I gave you my numbers.

 

[TBone2000]

Rereading my last response, I came across like an ass. My apologies. Thanks to you both for your help.

T

 

[boo1]

Typical 3/4" (19 mm) T@G 4'x8' sheets are installed (glued and screwed) perpendicular to the 2"x4" floor girder joist. This creates a composite section with point loadings (two) over four spans. The OSB acts as an unblocked diapham. The OSB design values are 2000 PSI across panel and 5000 PSI along panel (see:

http://www.buildabetterhome.com/pdfs/managed/TT-044_Mechan.pdf

)

PEinc's load per leg of 575# would be caused by four 250# people (one on each leg). LL is a temp loading so bending stress are subject too 1.6 allow stress increase.
Bending moment M ~ PL/4 is for a simply supported span (very conservative)
Span L=24"-3.5"(typ girder width)=20.5"
I thought a 325# loading was small for 3/4" sheathing, (i am one of the 250# men).
The indstry tests there products with 1" and 3" circular point loads.

http://www.apawood.org/pdfs/managed/Q225.pdf

http://www.apawood.org/pdfs/managed/D510.pdf

If the room is not complete just add a second layer on sheathing (glue and screw both layers). If the underside is accessable, add blocking between the girders where the table will go.

 

[TBone2000]

boo1,
Thanks for the detailed data/links. I spoke to the lead framer today... because the underside of the floor is still exposed, he volunteered to add blocking.

 

[PEinc]

I agree with boo1 that a simple span analysis gives higher moments than a multi-span analysis. I agree that, because the sheets are nailed and glued to each joist, you will not have a true simple span. However, you also will not have a uniformly loaded, continuous, multi-span condition. Also, you will not have a uniform load as assumed in the product literature that boo1 refered to. If the table is not positioned square with the floor joists, there may not be any load on the spans adjacent to a table leg. If you assume multi-spans, then the span length would be 24 inches. I don't see how you can subtract 3.5 inches from the span length, especially if you have joists narrower than 3.5 inches.

Although I checked quickly, I didn't see anything in boo1's referenced apawood links that indicated point load capacities for the flooring. If the information is available and shows acceptable capacities, great. Use it.

I agree that a person's weight is a temporary load but the table weight is a long term load. Using allowable stress analysis, I'm not sure how you could use two different load duration factors at the same time. Therefore, I would probably use the long term duration factor. Perhaps load factor analysis could be used.

I was not familiar with OSB flooring and assumed the T&G flooring was much narrower than 48 inches. boo1 is certainly more familiar with OSB than I am.

My main concern was, and still is, over how wide of a strip can the leg load be distributed. Where are the flooring joints? Can the T&G joint transfer this point load to the adjacent panel? I think it is wise to be on the conservative side with such heavy point loads on an upstairs residential floor. It seems to me that a second layer of flooring, with a staggered layout, would be prudent.

That is all.

 

[boo1]

I agree with all your points. Of course you are right with a conservative approach. If we were designing a structure, I would agree with different configuration. Here we are dealing with an installed system, and will it fail. My intuition and 20 years experience in the building industry say it’s marginal, but not catastrophic.

I had indicated above the loading was: "This creates a composite section with point loadings (two) over four spans." Typical residential floor girders webs are 2x4's turned sideways, reducing the effective span.


I tried hard to find examples of worked problems like this. Good references but no exact match. I hoped a more experienced guy could evaluate and add.

 

[swBausch]

You can check the before/after floor deflection from below.

If you have a stud detector and can align the legs to sit directly over joists, do it.


If the flooring sags, the pool table will communicate the fact to you by failing to maintain a level playing surface.


I worked a year in the customer service department of a very large pool table retailer, and we had zero concern for second floor installations. We would relevel a table for free during the first year of ownership. I can count on one hand how often it happened; usually it was blamed on the carpet compressing.

I know of only one situation where we 'gave up' on maintaining a table's levelness. Yes, it was above grade, but the floor had problems other than a pool table.