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RE: Welding of Crane Runways

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An additional though about intermittent welding in fatigue applications...

Fillet welds in fatigue (i.e., 20,000 cycles or more as noted by Bob
MacCrimmon) fail by initiation of cracks from the start and stop of the
weld. A continuous weld has one and one end and the other at the other
(duh!). An intermittent fillet weld has as many starts and stops as it has
segments.

So the basic difference is, a continuous weld unzips in fatigue from two
locations simultaneously, while an intermittent fillet weld unzips
simultaneously from a number of locations equal to two times the number of
segments. Assuming the rate of unzipping at each point is constant, it is
clear that the continuous weld will have the better fatigue life performance
and is preferred in fatigue applications.

Charlie





-----Original Message-----
From: Daryl Richardson [mailto:h.d.richardson(--nospam--at)shaw.ca]
Sent: Tuesday, November 05, 2002 1:41 PM
To: seaint(--nospam--at)seaint.org
Subject: Welding of Crane Runways


Fellow engineers,

        Since Gary's question was asked on the list I consider it
appropriate that Bob MacCrimmon's answer (which follows) should also
appear on the list.

        I will undertake to forward any further comments by any of you
to Bob since he is not one of those monitoring the list.  Bob's work in
progress will eventually become a published standard, therefore, any
contributions by any of you will be appreciated very much.

Best regards this election day,

H. Daryl Richardson



Subject:         RE: Welding of Crane Runways
   Date:         Tue, 05 Nov 2002 08:47:57 -0500

   From:         "MacCrimmon, Robert A." <RMacCrimmon(--nospam--at)Acres.com>

     To:         'Daryl Richardson' <h.d.richardson(--nospam--at)shaw.ca>,
                   Gary Hodgson & Associates <ghodgson(--nospam--at)vaxxine.com>


Thanks for the info and copy of Chris Wright's comments. Chris has gone
into considerable detail. My understanding is that the starting and
stopping makes this a series of "E1". We design for fatigue by the range
of stress and the category accounts for the severity of the situation.
As for fracture mechanics, I don't think we have to get into that.

I think it comes down to fatigue and whether the weld is subjected to
bending due to lack of contact between the top of beam and the U/S of
the cap channel.

I wouldn't be too concerned in a crane class A or B type service, below
20,000 cycles, but I'd avoid the stitch welds beyond that. I am aware
that continuous welding can increase the tendancy for separation of the
cap channel but I
guess that's part of the price for this type of detail.

Please feel free to comment. I am trying to incorporate suggestions for
lighter duty service into the guide and in addition to Daryl's previous
comments, Gary has already given me several helpful suggestions.

One further comment is that to paraphrase, S16-01 states that design of
welds is to S16, W59 is for construction.

R.A. (Bob) MacCrimmon, P. Eng.
Project Engineer
Acres International Ltd
4342 Queen St., Niagara falls, Ont., Canada
L2E 6W1
Phone 905 374 5200
Fax    905 374 1157




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