Appropriate use of Fy
Appropriate use of Fy
(OP)
If a structure is designed with A36 and someone made a very BIG "woops" (not me), and the steel is tested and comes back with Fy > 50 ksi I believe it is ok to use A572 or A992 for a second look (provided the other requirements of the standards are met). Is it appropriate to use Fy = say 61 ksi if that's what the test shows or are you limited to a max of 50?
Any opinions?
Any opinions?






RE: Appropriate use of Fy
That said, most A36 produced today will in fact have a yield reasonably consistent with A572 Grade 50. You can't call them the same thing because one is a carbon steel and the other is a high strength low alloy steel.
I would limit yourself to no more than Fy-50.
RE: Appropriate use of Fy
Remember, that the actual steel stress form a bell curve, so if there is steel that tested at 61ksi, where is the steel that is on the lower side of the bell curve...
RE: Appropriate use of Fy
RE: Appropriate use of Fy
I guess your code makes assumptions of ftu based on fty ... could you show that ftu of the material exceeds ftu assumed in the code?
RE: Appropriate use of Fy
RE: Appropriate use of Fy
RE: Appropriate use of Fy
RE: Appropriate use of Fy
RE: Appropriate use of Fy
If I'm reading correctly, it sounds like you're checking multiple members. If that's the case I would use the actual Fy for the member that was tested and for the others use Fy somewhere between 50 and 60. You could probably justify 60 if there's a reasonable certainty that the steel came from the same mill. I know it makes for tedious work but you'll sleep easier at night. This is not uncommon in bridge work; sometimes we're faced with rehabbing an old structure with no available plans.
If you're not dealing with any fracture critical members elongation shouldn't be a problem. If you need to retrofit members by welding chemical composition should be checked.
RE: Appropriate use of Fy
There might also be an IBC section (chapter 17) or ASTM out there that gives direction to this.
RE: Appropriate use of Fy
i think 61ksi is what the OP needs to pass the structure, and 50ksi is what the tests show.
JAE's right about determining a minimum strength from your population of tests; and your tets should cover each element, preferrably multiple times.
if i'm right about the 61ksi, i don't see how you can increase a test strength of 50ksi ... maybe plastic bending (form factors) can help. but your right that you probably need to check other things, like ftu/fty assumed by the code.
RE: Appropriate use of Fy
RE: Appropriate use of Fy
RE: Appropriate use of Fy
RE: Appropriate use of Fy
RE: Appropriate use of Fy
miecz-
Where in ASCE 11 does it talk about what strengths to use? I could only find what tests measure specific properties and couldn't find anything about if you are able to use the full test value from the coupon.
RE: Appropriate use of Fy
As I said earlier, ASCE doesn't explicitly state what to use. However, I believe it implies the use of the tested properties.
Article 2.3.3.3.
Also, as mentioned by bridgebuster, this type of analysis is commonly done in bridge work. Article 6.6.2.1 of the Manual for Condition Evaluation of Bridges states
I think that if ASCE or AASHTO expected the engineer to use something other than the tested properties, they would have clearly said so.
RE: Appropriate use of Fy
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RE: Appropriate use of Fy
That said, I see MTRs used on occasion to "establish" actual strength of existing structures, and that's treating a whole plate as if it matches the test coupon performed from somewhere in the same heat at the mill. However, the location of the mill test coupon, I believe, is chosen so as to give a conservative result, whereas a coupon from a piece in service will not have been taken from a similar location in the as-rolled plate. Appendix X2 of ASTM A6 has some interesting information about variability of tensile test results.
Hg
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RE: Appropriate use of Fy
Uniformity of the rolled products is an issue in this evaluation. Different shapes may have come from different mills, and at the least would be from different "heats" of steel. This means that their mechanical properties will vary and should be assessed for their uniformity and statistical minimums.
RE: Appropriate use of Fy
i guess if you're in a pinch and it's that particular member after there's a problem that's been caught. maybe.
just like in concrete breaks.
RE: Appropriate use of Fy
i think meicz hit it on the head. that's what i did when i would do structural evals.
RE: Appropriate use of Fy
RE: Appropriate use of Fy
I seem to recall a similar situation respecting the collapse of the Save On Foods Store in Burnaby, B.C. back in about 1980. The engineers breathed a sigh of relief when tests showed that the steel had a higher yield strength than expected so nothing was done to repair a seemingly underdesigned cantilevered steel beam (Gerber System). On opening day, a section of the roof (also used for parking cars) caved in on the shoppers below. Not a lot of fun for the engineers involved.
The locals joked that it was the "Cave In Food Store".
Best regards,
BA
RE: Appropriate use of Fy
Mike McCann
MMC Engineering
RE: Appropriate use of Fy
RE: Appropriate use of Fy