Calculating load on steel grating

[ryano669]

My company has been contracted to install a fire sprinkler system in a generating plant with steel grated mezzanines. We would like to be able to use drivable scissor lifts on the grating, but are unsure if the grating is suitable. The customer has informed us the grating has a 150lb/sq.ft capacity, and I assume this is "live load" as nothing else (machinery, pumps, etc) is supported by the grating. The lift weighs 2,400lbs. If we were to put plywood down over the grating, would it distribute the weight enough? How do we determine how much plywood is needed, i.e. one ¾" layer, two? Thanks in advance for the replies.

 

[broekie]

Many bar grating manufacturers list an allowable distributed load as well as an allowable point load in their literature.

 

[a2mfk]

I agree with Broekie, I would contact the specific mfr for more info.

Since the steel grate is much stiffer than plywood, I think the plywood would do little more than spread out the tire loads a few more square inches than if it were not there at all.

 

[TLHS]

I would also be concerned about the structure holding the grating. If the framing is only holding the grating, it's fairly safe to say that it was designed to the same loads as the grating was.

You should probably bring a structural engineer in to take a quick look at it. If it's okay it shouldn't take long to confirm it.

2400lbs isn't a huge amount when you're presumably dealing with steel, but it could still end up overloading light platform framing, especially once you add in a couple of people and equipment

 

[MiketheEngineer]

I would have an SE take a very serious look at this. I have done it a few times and was rather shocked at what loads it would(not)actually carry safely.

Also - if it is much older than 5 years or subject to noxious environment - you may find a lot of rust and/or deterioration.

Had a situation recently where some steel was practically gone after 18 months!! and people work right there!

 

[BAretired]

The grating load tables I'm familiar with show uniform load in psf and concentrated loads in plf. These are not really concentrated loads...they are line loads. Wheel loads are a different kettle of fish.

BA

 

[dcarr82775]

I've done this a few times. My methodology is to count on the bearing bars directly under the wheel and depending on what the crossbars are I may or may not include a couple of extra bars beyond the wheel. I always come up with only small scissor lifts being acceptable on paper.

I have put down steel plate to gain extra bars when needed. I doubt plywood would do much good at all.

 

[Brad805]

Assuming your boss does not have it in his quote to hire a SE to look at this, I think there is a couple of checks you can do yourself.

The allowable uniform loading is not really all that helpful, and you should check this for yourself anyway. Most bar grating is pretty similar, so you can find many different sources that will show you the allowable loading. All you need to do is measure a couple of things:

1. Grating depth
2. Bar thickness. 3/16" bars and 1/4" bars are pretty common.
3. Bar Spacing. 1"/2"....
4. Grating span
5. Transverse bar spacing.

From this you should be able to figure out what grating type you have. You need to check the allowable concentrated loading for your profile. Here is a link to a McMaster page. There are many others too.

http://www.mcmaster.com/#6849tac/=av121c

I doubt the plywood will do anything, but protect the wheels. The grating is likely far stiffer, so the little bit of wood will not help to increase the overall strength much. Steel plate can help in some cases, but is not always effective. You could always buy a few pieces of new grate designed for your machine.

Brad