Not may be but surely wrong... In most cases, ( except full tension elements ) the design is controlled by buckling capacity for columns or LTB for beams ...
The elastic buckling load of a column made up of S355 or S275 is the same since modulus of elasticity for almost all steels are the same..(Pcr=nΠ^2(EI)/lef^2) and the design buckling resistance of slender column will not vary substantially for S355 or S 275.
Pls do not assume offensive but when i see similar simple threads , i am getting really sorrow and thinking that we are witnessing the end of engineering...
I'm not so sure that's entirely true as the two materials mentioned have different yield strengths don't they. The axial capacity achieved is proportional to the yield strength after all.
Often lower strength steels are more ductile (higher elongation when tested before fracturing) would be another rather general observation. Not sure if that stands true for S275 vs S355.
You're assuming we know what you're talking about?
Ah...in the USA we have the same thing with the older A36 (Fy=36ksi) and the newer 50ksi steel. Where the higher yield strength is not needed, we still spec A36. We probably get 50ksi steel for those components most of the time.
We also have the same phenomenon with 40ksi vs. 60ksi reinforcing bars, where the 40ksi bars are actually more expensive from our suppliers. (The bars that fail the 60ksi certification get relabeled as 40ksi, and sold at Home Depot, etc.) We recently dropped the 40ksi from our specs completely, just to simplify our details. (We no longer have to designate ties and stirrups that are required to be 60ksi)
Rod Smith, P.E., The artist formerly known as HotRod10
I have edited the subject sentence but the axial capacity achieved is NOT proportional to the yield strength..
The use of S 275 ( St44 ) is not a norm in my region but S 235 (St 37 ) is a norm to go..If you need higher strength S 355 (St-52) is the common material...
I meant proportional in the sense the one with the higher strength will have a higher capacity (I wasn't suggesting linearly proportional or anything like that, but I wasn't that clear in hindsight!).
To clarify, given the same section size with different yield strengths, the one with the higher yield strength will have a higher buckling capacity under the same restraint conditions was the point I was trying to make in response to the statement that the buckling capacity was the same because the two different material have the same E.
To clarify, given the same section size with different yield strengths, the one with the higher yield strength will have a higher buckling capacity under the same restraint conditions...
Even if it were true in this case, which is doubtful, for a column it would seem to be irrelevant, since the column would have such extreme eccentricity by that point, it would almost certainly be buckled past the point of no return.
Rod Smith, P.E., The artist formerly known as HotRod10
The question wasn't posed by OP about columns, that was raised by hturkuk. I was more discussing the material property differences between the different grades.
Check the elongation requirements for both the S275 and S355 materials. There's a percent in it, and a few percentage points difference for the lower strength S235 material.
These are material specifications of course, but in general lower strength steels usually have a higher elongation requirement and hence elongation performance as I originally noted. This is true of European steels and other markets I'm familiar with. Of course in practice the elongation can be higher than minimums for all strength grades. But as a generalisation steel standards do tend to penalise the use of higher strength steels (>350MPa) when ductile behaviour is required for seismic conditions.
Depending on the slenderness, the difference can be very small.
Agree, with very squat columns the difference is an almost direct ratio of the yield strengths for the same sections under same conditions, but as the slenderness increases the capacities do converge further and the difference becomes less noticeable. The following exercise to my local code for a 50MPa grade difference in yield stress has quite a markedly different axial capacity for same section size until you get into reasonably high slenderness territory where they more or less converge on the same capacity (in practical design I feel like you'd be well below this point), the cutoff was a slenderness of L_e/r = 320. The only thing changed is the steel grade. Eurocodes have a similar formulation to my local codes for axial buckling as far as I'm aware.
For example, minor axis capacity is dashed line, solid is major axis capacity:-
The question wasn't posed by OP about columns, that was raised by hturkuk. I was more discussing the material property differences between the different grades.
Ah...I see that you're right. My comment was only meant as a caution that in some situations higher yield strength does not significantly affect capacity.
These are material specifications of course, but in general lower strength steels usually have a higher elongation requirement and hence elongation performance as I originally noted.
That's generally the case, but not always. However, the circumstances where the elongation before fracture from excessive deformation of mild steel would be considered in design, would be rather rare.
Rod Smith, P.E., The artist formerly known as HotRod10
I see. I had a large flood gate where the plate was s275 and beams/columns s355. And other than weldability I didn't know why the designer chose to use 2 different types
In the UK S355 is now the norm for beam and column sections. It will be more expensive to buy the same sections in S275, as these are not rolled regularly.
For plates S275 is the norm.
This may be why 2 different grades have be shown by the designer.
In the UK S355 is now the norm for beam and column sections. It will be more expensive to buy the same sections in S275, as these are not rolled regularly.
Sorry Rod for late response just seeing your comment now. Yes S355 can be used instead of S275.
Bear in mind that additional properties of the S355 (impact toughness, etc.) will need to be at least as good as that of the specified S275 product.
