## Floor rating 120psf, I do not understand

## Floor rating 120psf, I do not understand

(OP)

Hello. I have a floor with a rating of 120psf (0.83psi). I do not understand why I do not go thru' the floor as I put down at least 20psi. Can someone explain this to me and also advise me on the maximum load (and point load) I can place on this floor. I would also like to know how to work this out - thank you very much!

## RE: Floor rating 120psf, I do not understand

As to the 20 psi figure, this translates to a live load value of 288 psf. In that the design load was apparently for 120 psf (normally 100 live plus 20 dead), what is the reason for the nearly 300 psf requirement if I understand you correctly? Is this floor supporting heavy equipment?

Mike McCann

MMC Engineering

Motto: KISS

Motivation: Don't ask

## RE: Floor rating 120psf, I do not understand

There must be a mistake in your figures as no building floor I know of is designed for that. The highest loading I have ever used was a 400 psf roof snow loading for a ski resort in the Cascade mountains of Washington.

Mike McCann

MMC Engineering

Motto: KISS

Motivation: Don't ask

## RE: Floor rating 120psf, I do not understand

OK, my floor is rated at 120psf, yet a 200lb man puts down 20psi - why does the man not go through the floor. Why can the floor support this load AND heavier loads, and how do I calculate this?

It's driving me crazy - thank you for the help!

## RE: Floor rating 120psf, I do not understand

www.PeirceEngineering.com

## RE: Floor rating 120psf, I do not understand

The man does not go through the floor because the plywood is strong enough to span the point load to the joists, and the joists strong enough to span the reaction from the plywood to the beams. That's why the plywood is usually supported at 16 to 48 inches on center, depending on the thickness and the load rating.

You can ususally spread out the point load on a 24" square area, so the actual local uniform load seen by the plywood is closer to 50 psf for a 200# man.

Mike McCann

MMC Engineering

Motto: KISS

Motivation: Don't ask

## RE: Floor rating 120psf, I do not understand

I think you have mis-conception on contact pressure and material stresses (shear, bending,...).

Check on the label on elevator, it indicates how many persons and the weight limit. Then divide the weight limit by the floor area to see what psf you get. Then divide the psf by 144, now I think you would never want to step into an elevator.

## RE: Floor rating 120psf, I do not understand

By necessity occupancy loads need to be round rough numbers.

## RE: Floor rating 120psf, I do not understand