You'd have to go back a ways in North America before 36 ksi would be an unconservative assumption. When was your facility constructed? AISC Design Guide 15 should have everything that you need if you have access to that.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
If you have the original design loads and when you check several simple beams they are all significantly over stresses at 36 ksi, then I a would lean to the 50 ksi value. Although possible, I think it highly unlikely that mistake could have been made. Risky? Perhaps a little, but a calculated risk.
If still in doubt, clip a portion of a beam and have it tested.
msquared:
offtopic sorry, but,
"clip a portion of a beam and have it tested. ". how big a piece is typically needed, and, who performs such testing and what's range of cost, if you don't mind....
No it not an existing structure, it is small shed going to be build from some angle shapes.
The owner may have some angles with Fy 36 ksi. I was wondering if I design based on 36 ksi and then they see they don't have enough 36 ksi and purchase 50 ksi will my design based on 36 ksi be conservative or it will be underestimate
In the basic sense, 50ksi steel is stronger than 36ksi steel, so if the material is one or the other, designing for 36ksi is the conservative option. Stiffness isn't influenced by the yield strength, so long as your structure isn't designed to yield.
Of course, there are a few metallurgical characteristics where 36ksi steel may be better than a 50ksi steel (maybe fracture toughness, or weldability). I'm not a metallurgist, so I don't know specifically for A36 vs A572. But I doubt these affect your small shed.
That said.. do you have a mentor for this project? Seems like you may be having trouble with some fundamentals of structural steel. I'd encourage you to lean on whatever (non-internet based) resources you have.
I can not think of an example where assuming A36 and it turns out to be 50 ksi would be unconservative, in fact, for many recent years the actual yield stress of A36 could be in some cases much greater than 36ksi. As manstrom pointed out angles are typically A36 .
I believe it would be unconservative to assume a lesser yield strength for local buckling checks. Using Fy = 36 ksi would result in a higher (unconservative) limiting width-thickness ratio than permitted if the material, in fact, has a yield strength of 50 ksi.
@Hokie93: I think that local buckling checks would only be an issue if your were actually planning to take the elements of the section all the way to 50 ksi. If you're only going to stress things to 36 ksi, everything ought to be fine. On a purely intuitive level, it's hard to accept that you would make something stronger at the material level and somehow end up with less capacity. No doubt there are some arcane exceptions to this "rule" but, in general, I think that it's valid
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
Hokie93 is right, and Kootk is right about the rarity. There are indeed exceptions to the rule... When Canadian steel went from 300MPa standard to 350MPa, a number of beam sections went DOWN in strength.
Since I figured that statement is going to cause a riot, I went and dug out my old seminar notes and previous steel manuals. While not exactly the same, this is a very similar issue (ie: effects of material grade on an otherwise equal section)
Twenty or so beams gained little (less than 5%) from the increased stress grade. Half a dozen actually went down.
Nothing to rock the world, but the sections in question certainly didn't benefit the way you'd think... The difference from 36ksi to 50ksi is similar, only far more pronounced. Be very careful!
Are there any data points where the capacities actually went down by a significant amount CEL? I would consider 0.3 kN*m to really be staying put. And that's just what I would expect from a beam whose capacity was limited by local b/t buckling at the lower ksi:
1) Capacity wouldn't improve because elements would buckle at the lower ksi.
2) Capacity wouldn't decrease because elements could still make it to the lower ksi.
3) Design to the lower ksi would still be safe.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
None that were anything to write home about... It was just an interesting quirk. The reverse is even more pointed; If zi get a chance I'll run the numbers to double check. Gut says this minor issue at 44 to 50 is going to come out in spades at 36 versus 50, but I doubt it will ever govern.
Triangled....preferably a piece that is about 4 inches wide and 16 inches long. This will give both tension and elongation. 36ksi steel usually has a yield of 40+ ksi. Elongation will vary.
Cost is about $200 US per specimen here in the southeast US.
@Hokie - using a reduced yield strength for local buckling checks is actually a recommended way to use design equations intended for compact sections - ie reduce Fy to the point the section is classified compact, and use this Fy in your strength calculation.
@CEL - 0.3 kN*m seems like a rounding error somewhere. There are four ways a beam can fail - elastic lateral torsional buckling and local flange buckling(F.y has no effect), inelastic LTB and plastic/elastic yield (F.y increases strength)
