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Re: shear studs

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Everything is ASD: 11.5/7.3=1.57
----- Original Message -----
Sent: Monday, October 31, 2005 11:02 AM
Subject: RE: shear studs

Is it an LRFD vs ASD thing that?s getting you the 157% difference?

 

I remember the TRW stuff being in LRFD for some reason, it?s been a while since I looked at it.

 

-gm

 

-----Original Message-----
From: S. Gordin [mailto:mailbox(--nospam--at)sgeconsulting.com]
Sent: Monday, October 31, 2005 10:11 AM
To: seaint(--nospam--at)seaint.org
Subject: shear studs

 

List,

 

Here are some considerations related to shear studs in composite beams (say, 3/4" diameter).

 

1) According to AISC Manual, the capacity of such stud is 11.5k (according to Nelson TRW spec, that capacity should be adjusted for stud spacing, for example, 0.85 for 2 studs/rib).

2) According to Nelson TRW Manual #21, the tested shear capacity of the stud is 0.87Fu; the allowable capacity - with SF=2 is 0.425Fu, or, for the subject stud, 11.2k. These values are also presented in the curred ES report. 

3) Followng a regular shear design procedure, and neglecting any welding considerations, assume the stud-beam connection to be solid and limited by the beam material strength.  The allowable shear capacity of the stud will be 0.4Fy, or, for the subject stud, 8.8k (Fy=50KSI) or 6.3K (Fy=36KSI) <<11.5k.

4) The allowable shear capacity of a 3/4" dia A307 bolt (double shear, due to stud fixity) is 8.8k. 

5) This means that the allowable shear capaity of a stud is assumed to be at least 31% higher than that of any other comparable fastener or solid metal. 

6) Sometimes, studs are welded with fillet welds.  The capacity of such weld (E70, shear only) is 8.8k for 1/4" weld and 6.6k for 3/16" weld. 

7) According to AASHTO spec, the capacity of the subject stud (no fatigue) will be 7.3k.  That can account for AASHTO being slightly more conservative than AISC (83% of 8.8k capacity).  However, the 157% difference between the 7.3k and 11.5k appears too high for conservatism only.

 

My concern is not necessarily the adequacy of the stud shear connection (after all, it was proven to work).  However, the discrepancy between the allowable values we use for welded studs and for all other steel components is a little bit uncomfortable. 

 

Any thoughts?

 

Steve Gordin SE
Irvine CA