Why does the Epsilon value get reduced for Higher Yield Matl/steel?

[vhengr]

Hi friends,

As per BS 5950; the parameter (E) "Epsilon" =(275/Py)0.5 is used for Limiting width to thickness ratio for sections in Table 11. (where Py= Yield Strength of the Matl)

My questions:
01. Why does the Epsilon value get reduced for Higher Yield Matl/steel?
02. Can any one throw some light or provide any literature for the basis of value of 275 taken in the above formula of the yield stress ratio (epsilon)? [whereas in Indian Code- IS 800; the value of 275 has become 250 in the formula]

Thanks in advance.

Cheers! -VH

 

[briancpotter]

Not very familiar with BS5950 (or much of a steel design guy at all tbh), so take this with a grain of salt:

The epsilon is limiting width/thickness to prevent a section from buckling. As your steel strength goes up, your limiting width/thickness will need to go down to ensure it doesn't buckle at the higher loads. (Thought experiment: if your steel yield strength suddenly went up by a factor of 1000, your beam would obviously buckle long before it yielded).

Not sure about the 275, I suspect it's just a constant of proportionality. If India regularly uses a lower-strength steel, that could be the reason.

Brian C Potter, PE
Simple Supports - Back at it again with the engineering blog.

 

[MGZmechanical]

I think that the 275 is the yield strength for S275JR (275 N/mm2) a very common structural steel in Europe. Probably many test were made using this particular steel and the Epsilon is the adjusting factor.

Regards

 

[JoshPlumSE]

The local buckling depends on b/t, not on Fy. However, whether or not local buckling reduces the member capacity depends on Fy.

Let's say the local buckling of the flange would occur at 300MPa (based purely on b/t ratio, not on the material Fy). That doesn't affect the compression strength of the member when the material yield is only 200MPa, but it does affect the compression strength when the yield is 350 MPa.

 

[vhengr]

I feel, they have introduced this Constant to established relation between Yield strength and Ductility of the steel.

Is there any literature available for derivation of Epsilon value?

Cheers! -VH

 

[vhengr]

If anyone can throw some light on the topic shall be highly appreciable!
Thanks in adv.




Cheers! -VH

 

[Toby43]

Not familiar with those codes.
Nonetheless, if the buckling capacity of a member is related by the product of its Section capacity and a slenderness reduction factor
(Buckling Capacity=Reduction factor x Sectional Capacity)
then an increase in yield strength will increase Sectional capacity and the slenderness reduction factor must reflect this (as elastic buckling has little to tdo with yield), hence your 275/Py. 275 is likely the yield of the material in which the reduction factor was calibrated as others have mentioned.

Toby