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RE: LRFD vs. ASD Bolt Interaction

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The elliptical interaction curve and three-straight-line approximation of 
same are equally valid approaches to the design of bolts for combined shear 
and tension. The advantage of the elliptical equation is it is a continuous 
fuction (good for programming). The advantage of the three-straight-line 
approach is you don't have to drop the bolt shear strength when you have a 
very small tension (and vice versa). In the end, the joint design will be 
very similar with either approach.

If you want to know the basics of these approaches (or want to derive a 
three-straight-line approximation for yourself as you said), the 
development and basis for these is given in a paper I wrote with Ray Tide 
and Joe Yura. You can find it in the Third Quarter 1997 AISC Engineering 
Journal. It is titled "A Summary of Changes and Derivation of LRFD Bolt 
Design Provisions".


-----Original Message-----
From:	Zachary Goswick [SMTP:ZachG(--nospam--at)]
Sent:	Wednesday, August 04, 1999 9:19 AM
To:	'seaint(--nospam--at)'
Subject:	LRFD vs. ASD Bolt Interaction

I am looking at the interaction equations of ASD for bolt shear and
tension interaction.  The equations in table J3.3 for A325 and A490
bolts give an elliptical interaction line.  I am wondering if I can
apply the same type of modification to these equations as they did for
LRFD.  They simplified the elliptical interaction line with 3 straight
lines giving "minor" deviations.  I would like to do the same to the ASD
equations to be able to graph it easier.  Does anybody have any
experience with this conversion?  I am wondering if I can directly
convert the ASD allowable stresses using the equations given in the
commentary of LRFD?  Does anybody know why they didn't do this in the
first place.  Does it give unreliable results?

Zachary Goswick, EIT