ACI 318_Steel Anchor Ultimate Strength

[Wanna_be_SE]

In ACI 318-14, Section 17.4.1.2 and 17.5.1.2, it says "futa shall not be taken greater than the smaller of 1.9*fya and 125ksi".

I interpret this as IF your ultimate strength of steel anchor is greater than 1.9*fya and 125ksi, then you use the smaller of 1.9*fya and 125ksi. Is that correct, or is ACI 318 DEFINING the Ultimate strength to use, and not just LIMITING the Ultimate strength you can use?

In many cases (say A36 or F1554 Gr. 55) the Ultimate strength from material spec is less than the two limits set in ACI 318 (1.9*fya and 125ksi), so it doesn't make sense why you would automatically jump to smaller of 1.9*fya or 125ksi, if your already below those values. Why would you use a tensile strength greater than what's listed in the material spec?

 

[Greenalleycat]

I agree with your interpretation and that aligns with the wording in our code which has a restriction of fut < 1.9*fy or 860MPa (for shear), or simply 1.9*fy for tension.

The code commentary explains that "the limitation of 1.9fy on fut is to ensure that under service load conditions the anchor does not exceed fy. The limit on fut of 1.9fy was determined by converting the LRFD provisions to corresponding service level conditions."

Edit: I should also clarify that it would be possible to have a low yield steel that managed to fail the 1.9*fy clause even at low stress. So even if your steel was really shitty then you should make sure it satisfies that restriction for the ratio between yield and ultimate. However, unless you're buying some sort of god awful dodgy steel I would expect that the manufacturer would already be taking care of this for you. Hence, you only practically need to check the absolute limit.

 

[ProgrammingPE]

I interpret this as IF your ultimate strength of steel anchor is greater than 1.9*fya and 125ksi, then you use the smaller of 1.9*fya and 125ksi.

The "and" which I marked in red is not correct here. It should be "or" instead.

It may be understood more clearly in this form:

futa,calc = MIN(futa,actual, 1.9Fya, 125ksi)​

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[Wanna_be_SE]

Thanks for responses.

Yea if I was to set this up in MathCAD or something, I'd say what you said: min(futa,1.9*fya,125ksi).