Floor plate for safe 3

[charliealphabravo]

I am commenting on the appropriate size and thickness of a steel plate that has been used to support a 2000 lb safe with four feet on a wood floor system. The plate and the safe are about 30"x30" and the plate is 1/8" thick.

Between the flexibility of the plate and the floor system and the proximity of the feet to the corners I am having trouble convincing myself that the plate is effective.

 

[WARose]

What are you trying to do with the plate? Spread the load out? Cover an opening in the floor?

 

[racookpe1978]

How many legs does the safe have? Orr is the safe "flat bottomed"?

 

[charliealphabravo]

I think that the plate should be able to distribute the load to the floor system without regard to the location of the joists since it doesn't look like there was any attempt to align the legs with the joists.

From my initial calculations, the existing joists (16"D I-Joists, 8"oc, 16' span) are just barely adequate at 300psf for the indicated plate size so the configuration should not rely on direct transfer to the joists anyway.

I guess the bottom line is this...if I set a desired LL deflection criteria for the floor system (say L/480 or L/600 for the ATM) then is there a simple way to calculate the thickness of a 30"x30" plate loaded near 4 corners without resorting to some crazy second-order-differential-equation-plate-analysis-deflection-compatibility-study. I'd hate to have to dig out my old university notes

 

[charliealphabravo]

...and here is a pic. As you can see the legs are bolted to the plate so that might help a little but I think the stand was probably meant for a concrete floor, not a wood floor.

 

[Ron]

An 1/8" thick plate will have limited capability to spread a 500 lb point load off each leg.

 

[JAE]

Yes - agree with Ron - 1/8 in bending has very little stiffness and most of the leg load will be....simply a leg load on the floor.

 

[charliealphabravo]

Yes, I am with you guys. My second post was intended to indicate what an appropriately sized plate should be expected to do. It sounds like I was saying that the 1/8" plate is satisfactory.

 

[TLHS]

Yeah, that plate won't do anything.

Personally, I'd first check the number of joists that the load needs to be spread along. Then, if space allows, jack the safe up, install a couple of beams between it and the floor to span across the number of joists you calculated, and call it a day.

If space doesn't allow, and the joists directly under the safe footprint are adequate for the load, you may be able to do a similar thing by welding stiffeners to the upper face of the 1/8 in. plate.

From a material standpoint you'll get a much cheaper solution this way than trying to size a plate thick enough to do the same thing.

 

[woodman88]

If you have a plywood/OSB floor sheathing most of the concentrated loads testing done assumed a 4"x5" area for the load. Will the 1/8" steel plate spread the load that much? If I remember correctly, the maximum loads were over 1500# so at 500# you might be good.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[BAretired]

From my initial calculations, the existing joists (16"D I-Joists, 8"oc, 16' span) are just barely adequate at 300psf for the indicated plate size so the configuration should not rely on direct transfer to the joists anyway.

What does that mean? It makes no sense. You do not have 300 psf over the 16' span. You have 300 psf over a 30"x30" area.

Treat this as a concentrated load. If your joists are spaced at 8" centers, provide blocking to spread the load over, say six joists. Do not rely on the 1/8" plate to spread the load.

BA

 

[charliealphabravo]

hehe, I think it might be past your bedtime Master BAr.

I only applied the 300psf over the given plate size (30"x30") and a standard live load over the rest of the joist. Sorry if that wasn't clear. I only provided the span/depth/spacing as an FYI.

My point was that if the floor just barely works with a uniform distribution over the plate, then there is no point in trying to align the feet of the safe with the joist. The plate and subfloor must be designed to ensure uniform distribution to avoid overloading the joists.

 

[woodman88]

"The plate and subfloor must be designed to ensure uniform distribution to avoid overloading the joists."
No it doesn't. Whether the total load from the safe is applied as a uniform or as four concentrated loads the load to the joist is almost the same. The subfloor must be design to support the safe load however applied to the joists.
(I do need to learn about how to do the Quote insert.)

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[msquared48]

I regularly deal deal with spreading out 6000# loads on a 28X42 base on wood floor system, and will not use anything less than 1/2" plate.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[msquared48]

For this application I would strongly suggest placing a square of inverted channels at the edge of a 1/2" plate, all welded to it. This will stiffen the plate further to spread out the point loads better.

Depending on the numbers, you may be able to get away with thinner plate than the 1/2", but I'd start there.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[Ron]

CAB...don't forget that you have to get that safe to its final location. In doing so, you'll have to check the concentrated load of the dolly wheels and lifting device at various locations. In short, don't crack something along the way!

 

[BAretired]

Good point, Ron.

BA

 

[charliealphabravo]

Yes, thanks all. It looks like a reinforced plate is a more efficient solution and more straightforward to analyze then a pure plate analysis. There is also a 4600lb night deposit box that will have to be moved. I have no idea how they got that in there in the first place.