Steel Diamond Plate Analysis 1

[hemal1214]

Hi,

I am analyzing an existing platform in a mill. The grid of the platform is 16'x12' and it is supported by W8X18 steel beam between columns. There are two W8X13 intermediate beams placed 4'-0" o.c. There is a 3/8" THK. diamond pattern steel floor plate spanning 4'-0" o.c.

The client wants to use the platform to support lift truck which distributes 300psf total load on the platform. I need to check if the existing diamond plate is adequate or not. I also need to check existing framing supporting the platform.

Is there a way to check the adequacy of steel diamond plate? Need some advise.

Thank you.

 

[ATSE]

Maybe this is a trick question, but why don't you ignore the raised diamonds and treat like a flat plate?
For one-way action, 3/8" plate and 4'-0" span and 300psf, not pretty for strength or deflection.

 

[ToadJones]

table 3-18a AISC 360-05

PG 2-145 ASD 1989

 

[hemal1214]

Thank you ATSE and Toadjones,

I really appreciate your answers.

 

[JedClampett]

Is 300 psf the average load over the footprint of the lift truck or the tire load? Because if you're checking a tread plate, it's more likely that the tire load is going to control.
Be prepared for some scary big stresses.

 

[hemal1214]

Write now, I just have a 300 psf of average load over the footprint of truck. I have not exact ideas about how much would be tire loads. Say, If I assume the 300 psf of average load multiply with the footprint of fork lift and then distributed equally into 4 tires.

If I put point load on plate to create the worst load case scenario would it be adequate for the consideration?

Which software should I use to check the stresses? I just have Ram Advanse software which doesn't do a plate analysis. However, I might be able to download other demo software to check.

Thank you,

 

[JedClampett]

Forklifts have more load on their front wheels, usually 85% of the total load. The data I have shows the wheel load over an area 11 inch by 11 inch for a 5T capacity, but you should see if you can get the loads and area from the manufacturer.
As far as software, I would just do it by hand. Your software might go into some yield line analysis, where you'd rather stay in the elastic range.

 

[bradleyelwood]

hemal,

Mr Clampett had it right, the tire load by a forklift is NOT 300psf, over the whole area of the forklift.

Where I come from, I have seen the rear axle of a forktruck off the ground, putting 100 per cent of the forklift and load on the front axle. Then you ask, how does the pressure distribution between the tire and the plate look. As an approximation, use the tire(s) width(s) and for a pneumatic tire, the contact pressure is about 1.2 times the internal pressure in the tire. From this, you can calculate the length of the contact patch for the tire.

I agree with ATSE's comment. You are going to need more starch than the 3/8 plate and supports on 4 ft centers.

 

[dik]

If the inflation pressure of a truck is 100 psi... then it's only 3 in^2 for tread area....

Dik

 

[JedClampett]

dik, it must be late there. You can't convert 300 psf to a 100 psi tire tread area without knowing the wheel load.

 

[dik]

I agree... it was just a quick example to get a magnitude of the pressures to indicate that a 300 psf loading may not be representative of the wheel loading.

Dik

 

[JLNJ]

It won't come even close to working.

Hire a structural engineer to help.

 

[hemal1214]

I believe I should be more careful with loading the plate. Actually, the plate doesn't support a fork lift truck. It support Pallet Truck.

I am new to this pallet truck or fork lift truck loading. Does anyone know a good source which gives me a general idea about the loading on floor due to these trucks?

Thank you for your replies.

 

[JedClampett]

As I mentioned before, the manufacturers of these items will usually have these values available. If it's not on the website, you'll have to give them a call.
There's always the old fashioned way of calculating the values using the vehicle weight, lifted weight and statics.

 

[kingnero]

bradleyelwood,

"use the tire(s) width(s) and for a pneumatic tire, the contact pressure is about 1.2 times the internal pressure in the tire. From this, you can calculate the length of the contact patch for the tire. "

This is very interesting,
I used contact surface and tire pressure before to guesstimate weight, however I never took the "1.2" factor into account.
Could you provide a source for that? Or explain where it comes from?

 

[hemal1214]

"use the tire(s) width(s) and for a pneumatic tire, the contact pressure is about 1.2 times the internal pressure in the tire. From this, you can calculate the length of the contact patch for the tire. "

I am not able to follow this sentence. Is there a way to provide an example?

Say all 4 tires width is 8" and the internal pressure is 100psi. i.e. The contact pressure would be 1.2x100x8 = 960 lbf/in? How can I find the length of contact patch? or Say if the length of contact patch is 4 in, then my point load would be 960x4 = 3.84 kips?

So, the max. load from each two front tires would be 3.84 kips irrespective of the weight it is supporting?

Please correct me if I am wrong or misinterpreting

 

[bradleyelwood]

king...& hema...

The tire manufacturers give pressure "maps" of tires' contacts from experimentally determined loadings, lets call the maps "isobars".
It turns out that the max contact pressure between the tire and the ground is about 20 percent higher than the inflation pressure of the tire. The contact pressure diminishes somewhat as you go out from the center. For purposes of calculating bending and loading on floor plate, diamond plate, I simplified the explanation. I dont recall a reference. If you look at how tires work, as the load increases the tire patch length increases and the static deflection of the tire increases.

Let's try to explain the "phenomenon" with an example: imagine if you will a 17,000 pound capacity forklift which weighs 23,300 pounds, and lets put ALL 40,300 pounds on the front axle. (If anyone is interested in forklifts google "Hyster" for specs.) Now lets assume that 4 tires 9 inches width carry 40,300 pounds. Also, lets assume that the tires are inflated to 100 psi. (For the thermodynamicists in the audience, yes its 100 psi gage pressure.) We now have 1119 pounds per inch of tire width, so divide by 120 psi and we get the length of the tire patch as 9.33 inches.

If we assume that the pressure diminishes as we move away from the center of the axle and is 120 psi in the middle, maybe 80 psi toward the edge, and use an average of 100 psi, we get 1119 pounds per inch of tire width, 11.19 inches of tire patch length.

Whether we use 100 psi over 11.19 inches of length or 120 psi over 9.33 inches of length, the structural calculation is about the same.

All of the above petains to "forklifts" also called "forktrucks".

The only reason to explain all of the above is that similar discussions pertain to truck and trailer tire loading, etc. (For the race truck enthusiasts, we have to include some dynamic factors.)

A "pallet truck" or a "pallet jack" is quite different. A 200 pound "pallet truck" can lift about 2000 pounds or 4000 pounds and distributes the weight more or less evenly to 3 wheel sets. (Look on the side of the "pallet jack" and there will be a decal with the rating. If you cant find the decal, call OSHA.) Two wheel sets are under the pallet and a third "set" is under the jack-handle.

 

[dik]

Thanks...

Dik

 

[kingnero]

Bradleyelwood,

I've done the math before, however in the opposite direction.
For guessing what a trailer weighs, I've taken the dimensions of the contact surface of the wheels, and multiplying it with the tire pressure.

In this case there is a difference between the 100 and 120% pressure:
So when you take the actual contact surface, you want to work with the tire pressure at 100% .

Just an observation, as I never heard of that before...
(and have been pretty accurate that way without having access to a weigh bridge...)