Need help with understanding mezzanine loading

[Engineer2345]

Hi,

It was recently brought up at the place I work that the mezzanine could possibly be overloaded. I calculated the point load on some 50 gallon barrels (the heaviest thing we have up there). Each barrel is 22.5" in diameter and weighs 200 kg. I calculated a load of ~160 lbs/ft^2. The mezzanine is specified to a max live load of 100 lbs/ft^2. My initial thought is that these barrels should not be up here, but the other engineer in the office told the boss that it is ok, nothing to worry about. Supposedly they specified these barrels when they built the mezzanine (before I came here), but didn't know the exact weights of them. I figured the engineer used water as a guess, but this still gives me ~151 lbs/ft^2. We store 12 of them on 2 rows of 6 almost against each other. There is very little chance of them all being full at one time. Should I be worried about this or could this be acceptable?

Thanks.

 

[ztengguy]

If you look at the floor space 2 rows of 6 against each other takes, its 42.2 square feet. 12 full barrels is 5280lbs, so about 125lbs/ft^2. Now, does the mezzanine only measure 42.2ft^2, or is there walkways, open space, edge distance from barrels, etc, that would lessen the live load? I think some engineering judgement should be used here too, if you say they will never all be filled, but it could happen. If all the barrels are over 1 beam, it might be a bit overstressed, but again, other floor space not with barrels lessen that chance.

Perhaps a sketch of the mezz, and the barrel locations? A little more info would go along way. Whats the mezz made from?

 

[Engineer2345]

The mezzanine is pretty large (100' x 30') or bigger. There are offices at one end, equipment on the other, storage going towards the middle from both ends, and the barrels almost in the center. There is open space around the barrels (6' out from each long side, and probably 4 1/2' at one end, and an open aisle on the other end.

It is a concrete slab, and it looks to be 5 1/2" thick.

Sounds like it's probably nothing to worry about then?

Thanks.

 

[ztengguy]

Depends who brought up the issue to worry about it? If your just wondering, I would say off the record that its ok the way you described. If I was you and my job depended on my answer being correct to my boss, or if I was in the office below where the barrels are stacked, I would not ask on line, I would hire a structural engineer to review, and to post a floor rating.

 

[JAE]

I would hire a structural engineer to review, and to post a floor rating.

Agree here. You need to hire someone to check it properly.

 

[TXStructural]

I agree that hiring a structural would probably solve the problem. But for explanation, the members (slab, beams, columns) would have been designed for a uniformly-distributed live load of 100 psf (the load you gave us). This means that the actual design capacity would be somewhere about 40-60% above this (load factors.) Also, where members are partially loaded, as where there are barrels on one end and open walkway on the other, they "average out" according to the moments created by the actual load distribution. Also, you have to consider the effect of moving full barrels through aisles, including people and whatever handling equipment is used.

Where I have encountered this, I usually specify that all barrels be accessible from an aisle, thus limiting the problem of stacking them deep without rows. In your example, giving each barrel a full 24" square (rows of barrels 1-1/2" apart), without nesting barrels tightly, keeps you at 110 psf. But it's failure of the human element programs where things all too often go wrong.

 

[Engineer2345]

Well it was another guy who brought it up, who noticed a small crack in the concrete 15 feet from the barrels and apparently automatically attributed the crack with the weight. My boss and his boss say everything is fine, so I can't hire someone else to look at it. After looking at what the "crack spotter" is pointing out, it looks like the crack may be a result of hvac installers cutting through the mezzanine to install ductwork. The crack runs along the ductwork on a few places. Everything around the crack still seems sound, so I guess I'll just keep an eye on it for now.

Thanks for the input.

 

[TXStructural]

When you say "cut through the mezzanine...", this begs the question, "cut through WHAT exactly?"
If the slab is the structure, and the concrete and associated reinforcement was cut randomly, it could well have made the original design irrelevant. You may well be dealing with a significant capacity problem, and the first sign of impending failure might be a crack, or it might well be a sudden collapse. The location and character of cracks, the location and size of the ductwork holes, and the overall structural system layout are all critical in evaluating your mezzanine. You should probably get that looked at since it is loaded at or near design capacity and has been modified.

This is why reputable engineers and doctors don't practice on the internet.