Eric,

The result is the same in LRFD (strength design) for both ASCE8-01 and AISC 360. Note that there is a newer ASCE8 that I dont have, but I dont expect much change. If you are using sheet steel, less than 3/16" material, you should have ASCE8 as well as Design Guide 27.

As for the use of omega, if you just divide the ultimate tensile capacity by omega to get the allowable tensile capacity. LRFD capacity = 1.5 * ASD capacity. The 1.5 is considered the average load factor so the result should be same in most cases. You can look in the AISC 360 and both ASD and LRFD capacities are given in some tables, and the difference is always this 1.5 factor. If the actual LRFD load factor is not exactly 1.5, so the ASD and LRFD results will never be exactly the same, but close enough. I think it was the 13th edition (2006) of AISC 360 that the ASD was put back in (since the 9th (1989)) to accommodate the working stress design holdouts. Although I came from the working stress design era, I have moved on to LRFD. The 10th, 11th and 12th were LRFD only, but did not sell too well because of all the holdouts.

For shear it is the nominal area if the threads are excluded. Bolts A325 or A490 will have threads excluded is there if the outer layer is more than 1/2" with proper stick out. For stainless bolts or say SAE bolts you would normally assume the threads are included, unless you know for sure the shank is in the shear plane (unlikely, so not conservative). If the threads are included in the shear plane, the nominal area should be reduced by a factor of 0.75. This is approximately the net area/nominal area. The shear strength is 0.60 times the tensile strength otherwise (threads excluded), so for threads included it is even less (0.60 times 0.75).

If you are a member of AISC, you are entitled to all the Design Guides in *.pdf free. There is a substantial reduced fee on hard copies such as the manuals. There is a reduced fee on courses.

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James Mackenzie S.E., M.ASCE

Burnaby BC

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Original Message:

Sent: 12-13-2020 08:49 AM

From: Eric Heiberg

Subject: Safety Factors, Stainless Steel Bolts

James, Jayesh,

Thank you! I have purchased Design Guide 27. James, in your text, you mention Fnt as 56 ksi...I assume that 56ksi=.75*75ksi (for SS type 31600) and therefore the allowable tension in the bolt would be FntAb/omega or .75*Fu(Ab)/omega= .75*Fu/2 = Fu/2.67 for ASD (26250psi times bolt area for 70 ksi 31603 and 28125 times bolt area for 75 ksi 31600. Obviously this load is higher for stronger batches with certificates of compliance).

You mentioned that the bolt area is the area from the nominal diameter...I am assuming that I use that value only for shear loads going through the shank and that for tensile strength I would use tensile area and for shear through thread plane that I would use the minor diameter area.

Does that sound right?

Eric

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Eric Heiberg P.E., M.ASCE

Long Valley NJ

Original Message:

Sent: 12-12-2020 12:23 PM

From: James Mackenzie

Subject: Safety Factors, Stainless Steel Bolts

AISC Design Guide 27 is what you should be using for Stainless Steel (2013 is what I have, and that is probably latest). It is similar to the AISC 360 code for carbon steel. Chapter 9. Formula J3-1: Rn=FnAb phi=0.75 (LRFD) omega=2.00 (ASD) Fnt=0.75Fu Fnv=0.45Fu Ab is nominal (not net) area. Some properties are given in Chapter 2 and that is a range of 75 to 100 for Condition A in Table 2-4, so your 75 is good.

ASCE8 also has information on bolts. The last code I used ASD in was the AISC in 1989, and I dont see ASD in the ASCE8-02. Pn=AbF phi=0.75 (same as AISC). Fnt is given in Table E6 and yes (same as AISC) there is 56 ksi for 304/316 in footnote b Condition A in ASTM A276-85a, hot finished and Class1 (solution-treated) in ASTM A193/A193M-86. Note that Fnt is valid for ranges of diameters of bolts, but in this case it is all. For shear you would have to divide the area by 1.33. Also for diameters less than 1/2" use a factor of 0.90 footnote g (I dont think AISC says anything, but the line in the sand there is 1/2")..

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James Mackenzie S.E., M.ASCE

Burnaby BC

Original Message:

Sent: 12-11-2020 01:17 PM

From: Eric Heiberg

Subject: Safety Factors, Stainless Steel Bolts

Thank you in advance for your time devoted to this request.

I am looking for guidance on where to find the appropriate safety factor for stainless steel bolts in TENSION in ASD design, in a standard document (such as AISC, ASCE,etc). I have found some somewhat conflicting definitions/direction in the literature;

- A Power point from AISC that says use the same as for carbon steel (LRFD = .75*Fu) (this definition combined with another AISC publication: "Specification for Structural Steel Buildings", that defines ASD safety factor as 1.5/LRFD factor yields 1.5/.75=FS=2...this gives a value that is higher than the yield strength of a SS bolt (316 SS condition A; Fu = 70 ksi, Fy = 30 ksi This does not make sense to me))
- The Nickel institute produces a handbook entitled "Stainless Steel Fasteners, a systematic approach to their selection" that states that designers should use Yield strength for design (but that reference does not specify a safety factor, it just says one should be used). This document does provide a specific safety factor of 3 (Specifically 0.6Fu/3) for shear but does not provide any safety factor for tension.
- The Steel Construction Institute issues a "Design Manual for Stainless Steel" that provides a "partial factor" for SS bolts of 1.25
- Online I found a reference that indicated that such a safety factor might be found in "section J4" that did not reference a document
- Online I found a reference that indicated that such a safety factor might be found in ASCE 8 ... I am willing to purchase this document but would like a comfort factor that it will provide me with the correct Factor of Safety before spending the money.

Can someone point me to the right document?

Eric

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Eric Heiberg P.E., M.ASCE

Long Valley NJ

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