Fy for Structural Fasteners

[StrEng007]

Can someone advise as to why the AISC (13th Edition) does not list the Yield Stress for a majority of it's fasteners? Table J3.2 lists the nominal stress of fasteners and threaded parts as the Nominal Tensile Stress and Nominal Shear Stress, where it appears as though these values are derived from the Ultimate Tensile Stress for the material. However, when designing tensile members per AISC Section D, there are design checks for both the Yield and Ultimate values. Here I find that the nominal tensile yield strength typically governs.

I've always used these equations (corresponding to Section J) with no problem. However, I'm wondering why there isn't a relation to yield values for these fasteners (ASTM A325 for example).

Thanks!

 

[JedClampett]

Unlike softer structural steels, high strength bolts don't have a well defined yield point. The line is straight for a while, then makes a slow turn to the right, before it levels off. See the link below.
So the yield strength isn't applicable. They use such parameters as "stress at 2% deformation" to define a pseudo yield point.

 

[BadgerPE]

AISC does not include the yield stress because it is "not specified in the material specification" (Footnote - Table 2-5) which for most, means ASTM does not list yield stress in their tests. However, doesn't the user note at the beginning of Chapter D say to use J.3 for threaded rods? I think this would mean all bolts in tension are governed by the provisions of Chapter J vs. Chapter D.

 

[StrEng007]

Thanks guys.

Badger, yeah I realized that note is there... I'm stuck on WHY it does that. Would you attribute that to what Jed said about high strength bolts not having a clearly defined yield point? I'm trying to put together why I should be concerned about Fy for some tensile applications and why Fu is the only value that matters in other applications.