Grating Analysis 1

[IlliniPE]

I have a client wanting to use a lift truck to move pallets around the second floor. The floor is currently just steel grating. The lift truck and pallet together are about 6300 lbs which equates to a distributed load of about 605 psf. I calculated the grating can only withstand 250 psf. The idea would be to place diamond tread plste on top to provide the extra strength. I found some load tables for this, and it looks like the capacity is 521 psf for 5/8" plate at my 4' span.

By combining these capacities, am I being overly conservative? Could the diamond plate be assumed to have a shorter effective span because it's being supported by the grating?

 

[dik]

I haven't done it for a decade or so, but I've used steel grating in aircraft pavements and hangar floors capable of supporting fully loaded Boeing 747s... You can get stuff that works...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[SWComposites]

I don’t think you can sum the strength capacities. You have to account for relative stiffness of each.

 

[human909]

It sounds like you are out of your depth if you think that by simply laminating spanning members you can sum their capacities.

 

[dik]

That's why I suggested 'real' grate material...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[IlliniPE]

You can get stuff that works...

Changing the grating isn't an option. That's why the idea to add tread plste was introduced.

I don’t think you can sum the strength capacities

It sounds like you are out of your depth if you think that by simply laminating spanning members you can sum their capacities.

Perhaps "combining these capacities" wasn't the correct phrase to use. I didn't simply sum 250+521 and call it good. I calculated the section modulus for the tread plate and combined it with the grating to have a sort of built-up section. Do you disagree with this?

 

[ETX]

Unless you are rigidly connecting the two sections via welds, clamps, bolting, etc. then you cannot combine the section modulus for the built-up section. The built-up section has to be connected to transfer the shear flow and stresses to extreme fiber if you are going to credit the combined section.

The relative stiffness of the two sections have to be analyzed. You can use the force method to calculate the load distributed to the grating and plate for a unit width. The stiffer section will take more load and you can throw the equations in excel and goal seek to determine the maximum allowable load until one of the sections reaches its maximum allowable stress and that will be the limiting factor. Hope that helps.

 

[dik]

You have to connect the two compositely and hope that the combined strength works. There could be several issues due to the inadequacy of the initial grating. You might be far further ahead if you use new grating intended for the purpose.
----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[IlliniPE]

The built-up section has to be connected to transfer the shear flow and stresses to extreme fiber if you are going to credit the combined section.

I agree. I planned to have them weld the plate to the grating, but I'm realizing now I should probably check with them to make sure they are even able to do this. I'm thinking it's going to be more economical to just put a 3/4" plate down, but then comes the added weight consideration. I really appreciate the advice!

There could be several issues due to the inadequacy of the initial grating. You might be far further ahead if you use new grating intended for the purpose.

I think I'm beginning to see this is the case. Either remove and replace the grating, or get tread plate that's thick enough to carry it alone. Just a lot of steel to be added in the case of the latter.

 

[JedClampett]

Converting the truck and load to a distributed load is not enough. The wheels are going to be small, concentrated and hard. Forklift loads are actually much more severe than HS20. Here's a sheet out of the Grating Pacific Catalogue showing spans for different type of grating and loadings. Maybe if you build up your grating with plates welded to it until it matches an acceptable section property or replace the grating with one with a tighter spacing. Note that the grating gets very deep, very fast, especially for a 4'-0" span.
If you're out of options, saying "no, take the loads a different way" is an answer.

 

[dik]

Thanks, Jed...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[IlliniPE]

Converting the truck and load to a distributed load is not enough. The wheels are going to be small, concentrated and hard.

Agreed. Distributed loads were used for more of a talking point. In either event, I'm looking at a 1350 lb point load that will have to be absorbed by tread plate and distributed, to some degree, to the grating. I appreciate you sharing that table with me! Definitely a helpful reference to have handy.