Determine floor load bearing capacity

[MattH]

I have an electronics lab in a second floor house bedroom. I currently have 4 server racks, probably each around 500-600lbs (loaded) and enough equipment to fill up another 2 racks. This is starting to get me worried about how much weight this floor can take. I saw that residential floors are required to support 30-40 psf. Is that right? My racks exceed this locally (but then so do I), but the total weight is well below the total weight based on that psf (floor is 250 sq. ft.).

Unfortunately I don't know much about this floor (construction materials etc) as I'm a renter. But, it is a fairly old house. Anyway, I appreciate that I'm probably providing inadequate information to answer this question with any sort of conviction.

Is there a way to determine if a problem is occurring? I did take a level around the room looking for floor bending under this load and didn't notice anything (it's all pretty flat).

Any other thoughts? Things I should consider?

 

[billconner]

A bollard ball is an ideal floor levelness tool.

Hard to assess but probably if near a load bearing wall - not in center of span - not too serious. Take seriously any ceiling cracking below. It would be interesting to survey total floor load in that room or area and see if it was near the design load.

 

[strutaeng]

That's quite a bit of weight. Can you simply relocate the racks so they are not all in the same spot? If you can locate a wall underneath, put them there. Yes, 40 psf is standard live load rating for residential. But plenty of old construction framing out there wouldn't meet that. Where are you getting 250 psf?

This week I went to look at this mezzanine inside a warehouse where the client had concerns over floor sagging on the mezzanine level. Typical, "no drawings, we bought the building like this." It's wood framing and apparently a pre-existing load bearing wall was removed and some steel angle contraption header was installed, apparently by the previous owner. Sure enough, a lot of the existing framing doesn't check out for prescribed live loads, and neither does the header contraption.

 

[MattH]

That's quite a bit of weight. Can you simply relocate the racks so they are not all in the same spot? If you can locate a wall underneath, put them there. Yes, 40 psf is standard live load rating for residential. But plenty of old construction framing out there wouldn't meet that. Where are you getting 250 psf?

Fortunately, they're sitting on top of a wall that separates outdoors from indoors on the floor below. How much would you expect that to increase the psf?

250 sq. ft., not psf. 250 sqft x 40psf = 10k lbs, which I'm way below. But, admittedly, the weight of my stuff isn't equally distributed over the entire floor.

 

[rlitman]

Fortunately, they're sitting on top of a wall...

And that may be all you need. There's a huge difference in how a floor reacts to a load straddled over a wall vs mid-span.

 

[Zeke]

@billconner is right, put the stuff near a load bearing wall first, then any wall 2nd. Not in the middle of a span. And just so you know, there is a live load as well as the static load. Keep track of your figures but don't count on the old house to comply (as mentioned).

 

[strutaeng]

Fortunately, they're sitting on top of a wall that separates outdoors from indoors on the floor below. How much would you expect that to increase the psf?
Fcff
250 sq. ft., not psf. 250 sqft x 40psf = 10k lbs, which I'm way below. But, admittedly, the weight of my stuff isn't equally distributed over the entire floor.

Oh, my bad. I misread that.

I see. You are probably okay then. If you are directly under a wall, then you really don't load the floor joists in bending.

Without member sizes, spacing, layout of the loading, we won't be able to give a number, however.

 

[73fxe]

I'm working on a house built in 1925. The second floor was 14' 2x6 joist spliced 4 or 5 foot away from the interior bearing wall, with a lath and plaster ceiling. All load tables say this is impossible but it lasted over 95 years.

 

[firebirdparts]

I agree with this anecdote above being instructive ^^^^^. My experience with old houses is that they're quite weak, and they sag, but you generally don't fall through. typically an old house, if it's old enough, doesn't look "good' for 40 psf. And some, like the above, look like they're held up by the wind. That said, you're right about the racks. they really don't weigh enough to matter much. If a crowd of people goes into the lab then you may really have 40 psf of actual weight. I've never heard of a house collapsing under these conditions. Just balconies and outdoor stuff.