Design of Structural Steel Plate

[Dave_Immortal]

Hi everyone,

I am struck at the Design of Structural Steel Plate at the base of Dumpster where it is supported by 09 nos. S Beams.

I am confused with the design of Steel plate whether it has to be designed using Roark's Equation of Stresses and Strains or simply using the Bending Criteria. My both Calculations sheets are attached.

Please guide me if I am wrong anywhere in my design approach or missing any design steps in my calculations.

Thanks in Advance.

 

[bridgebuster]

Honestly, why not flip a coin? Either method works.

 

[Bagman2524]

Either works. Roark would be more accurate.

Nearly all men can stand adversity, but if you want to test a man's character, give him power. Abraham Lincoln

 

[JLNJ]

If your bottom plate is continuous, you might be able to reduce the design moment a fair amount and skinny up your rather thick plate.

I see that you are comparing your load against an allowable of .9Fy. I presume that this means your uniform load is already factored?

 

[BAretired]

Your calculations appear wrong to me. Are you really designing for 300kN in the shaded area? Seems high for a dumpster. That would be more than 300kPa.

In your calculation of moment, you use a span of 0.4m.
In your calculation of Section Modulus, you use a width of 0.4m instead of 2.4m.
In your acceptance criteria, you compare f_b to F_y or, more correctly φF_y. This would suggest that the load is factored.
If the load is factored, your deflection calculation is wrong.

BA

 

[BAretired]

Your deflection calculation is also wrong because you used an I value based on 400mm width instead of 2400mm.

BA

 

[Nor Cal SE]

I have a few thoughts:

1) I agree with JLNJ about the continuous plate having slightly less maximum moment than what you've calculated (probably closer to wL^2/10 instead of wL^2/8, though you can double-check that).
2) I agree with BAretired about using 2.4m width for section modulus, because that is the full width of the section. Note that per AISC it is most accurate to use Z instead of S, which is a 1.5 increase for a rectangular section.
3) On the last page, though you stated phi as 0.9, it appears you accidently switched to 0.75 on the line where you multiply it by 250 MPA.
4) Deflection is primarily a concern for perceptibility (i.e. people standing on a floor would feel awkward with excessive deflection) or when the deflection would prove detrimental to any object attached to the structural member, like a brittle brick veneer on a wall. It's possible you have no such constraints here, which would render the deflection check not critical.

 

[Dave_Immortal]

Hi BAretired,

Thanks for your comments. Yes, we are designing the structure for such a high load (unrealistically high).
I was confused in my calculations whether to use the span of 2.4m or the clear distance between the supports i.e. 0.4 m to which I chose to use the distance between supports.

Yes, you are correct I should have check deflection under service loads not the factored loads.

Thanks JNLJ,Nor Cal SE for your comments as well. I will double check the moment in continuous span as well.
However, the prime concern is to design the structure such that it withstand the high amount of load that it will be subjected to.


Please guide on the design of plates so as to make sure that it has sufficient thickness to withstand the high loads.

The prediction of stress using Roark's equation of stress and strain is different from this calculations.

 

[JStephen]

It would help to know how this work was normally done.
For example, it may be reasonable to treat the plate as a catenary between spans, which allows much larger spans.
Or it may be customary to arbitrarily thicken the plate over what uniform loading would suggest due to point loads.
For example, a dump truck bed would last forever if all you ever hauled it in was sand. But start hauling riprap, rubble, scrap metal, etc., and it starts getting dings in it here and there and looks bad after a while.
How is dynamic/impact loading handled (loading, unloading, hauling, dropping stuff in it)?

 

[BAretired]

Not sure if I have the loading correct, but I am assuming 300kN is a service load on the hatched area 0.4m by 2.4m.

Service load W = 300kN
Service load w = 300/0.96 = 312.5 kPa
Span L = 0.4m
Consider end span strip one meter in width
M = wL²/10 (positive and negative) = 312.5(0.4)²/10 = 5kN-m
Factored Moment Mf = 7.5kN-m
Mr = φFy.Z = 0.9*250bt²/4 = 225bt²/4

t = (7.5*4/225b)^0.5 = 11.54mm

Could use 1/2" plate.

BA

 

[dik]

Does it matter if your bottom plate deforms a bit? Can you use the plastic section bd^2/4 rather than bd^2/6? How is the plate welded to the steel beams? Can you use the clear span? if sufficient weld, can you use ql^2/12 for the interior (the thickness of the flange will be approx equal to the thickness of the plate, and you could treat the plate as being 'fixed' at the edge of the flange) You could reduce the end span a tad to give a propped cantilever moment equal to ql^2/12?

That's the approach that I'd use... to try to minimise the weight of the container.

Dik