To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
Subject: RE: fatigue category
From: Paul Crocker <paulc(--nospam--at)ckcps.com>
Date: Tue, 20 Feb 2001 14:21:02 -0800
It's been a while since I've done fatigue work, but I would have guessed
"C". From your description (which I'm not sure I completely understand) I
would guess that it is a stress concentration in a primary member outside of
a connection area. In the AISC manual, this sort of thing could be
represented by cases 7 or 22. Cases 23 and 24 are similar, as they involve
a stress concentration being introduced into a longitudinally loaded member
by a non-primary connection to it. These can vary from C to E'. I don't
have an AASHTO handy to see what their comparable case is. However, one
cannot safely assume that just because it is not a literal connection that
it would not behave as one, since it is still a hole through the member
(although you probably avoid many of the distoritional effects that can
occur at a major connection). There is probably more specific research you
could refer to, but don't be suprised if you get a large scatter in the
results. Fatigue design can be very subjective. Small changes can have big
consequences. I did my master's thesis a number of years ago on some
fatigue design issues, and was amazed at how different the analysis was if
you assumed one category versus another. Making matters worse, many of the
categories look awfully similar, even after careful consideration.
Paul Crocker, P.E.
From: Dave Evans [mailto:DEvans(--nospam--at)tnh-inc.com]
Sent: Tuesday, February 20, 2001 1:11 PM
Subject: fatigue category
Does anyone have a reference that specifies the fatigue category
for base metal with a small (say 1" dia) drilled or cored hole in it?
This is NOT a primary bolted or riveted connection as shown in the
typical fatigue category illustrations in AASHTO, AREA, and AISC;
the hole just permits a proposed retrofit appurtenance's bolt to
pass through the flange of a girder.
One of my refs says category A, which I want to hear, and the
other says category D. Category A is from the Structural
Engineering Handbook, 3rd Ed, by Gaylord^2 (illustration 28 on
page 4-8...but size of hole not shown, hole presumed centered),
and Cat D is from Bridge Engr Hdbk, 1st Ed, by Chen and Duan
D a v e E v a n s
T N H, I n c.