required) have often times removed the backing just to pass the NDT easily.
Back about 30 years ago, welders would use brass or ceramic backing plates
to make it easier to remove them, arc gouge the trash at the bottom and weld
reinforcing welds just to pass the NDT. Ceramic and brass will not fuse to
the weld.
Today, it is no different. We engineers in our arrogance and ignorance (me
included) have assumed that we have to lead a welder by the hand to get a
good performing weld. OK some welders need a spud wrench upside the head,
but most of them know how to get it done.
Consider the ever present fusion stud weld. It uses a ceramic ferule to
contain the molten fusion steel weld. It is as good of a weld as it gets
once the process is set up.
Many iron workers today use a ceramic back up bar. It is clamped or taped
in place. Some really sharp welders have had chamfers placed on the back up
bar. A well performed weld will then look like it has had a reinforcing
fillet weld on the back side, but it just the weld filler of the root bead
conforming to the shape of the ceramic back up bar.
Believe me, a good welder will do just about anything to avoid an overhead
weld and the resulting sparks down his shirt. With a little practice, I can
make any full pen weld look like it had a steel backing bar removed, back
gouged, and a reinforcing fillet weld. This weld can be shown in a symbol
by showing the fillet on the same side of the line as the full pen symbol,
and we can eliminate all of the problems with the backing bar removal. This
weld can be performed entirely from the down position just because a good
welder will want to get it done quickly and easily.
Check this out:
www.structuremag.org/archives/2006/February-2006/C-BB-Weld-Backing-Feb-06.pdf
Regards,
Harold Sprague
>From: bart@nbse.com
>Reply-To: <seaint@seaint.org>
>To: seaint@seaint.org
>Subject: RE: Backing bar in RBS steel moment connection
>Date: Fri, 18 May 2007 14:41:24 -0700
>
>For one thing, the bottom flange backing bar is located at the most
>extreme location as fas as stress, at the top flange it is not. AISC 358
>mandates this as well. There is a rather extensive commentary in AISC
>341 which may have more information. Both are free at the AISC web site,
>last time I checked. Additionally they found many problems stemming from
>the Northridge earthquake (parking structures being another one,
>which may be one reason they may have mandated I=1.25 for large
>structures, different subject) But there has been an inordinate amount
>of research done in this area. There is a Structural Engineer from the
>Bay area who spoke for AISC at the steel frame seminars that had been
>going around the country (whose name I don't recall) who was very bright,
>and can speak to this issue at great length. (He was also very adept at
>answering a lot of design questions) There are many engineers as well,
>who are on the SAC committee, for FEMA 350 etc, who can speak at great
>length about this issue as well. I know recently AISC printed the
>prequalified RBS connection, someone may know of a link to that diagram.
>
> ----- Original Message -----
> From: "Michel Blangy"
> To: seaint@seaint.org
> Subject: RE: Backing bar in RBS steel moment connection
> Date: Fri, 18 May 2007 12:00:04 -0700
>
>As usual excuse my ignorance, but why only the bot. flange? MB
>
> -----Original Message-----
> From: bart@nbse.com [mailto:bart@nbse.com]
> Sent: Friday, May 18, 2007 11:47 AM
> To: seaint@seaint.org
> Subject: RE: Backing bar in RBS steel moment connection
>
> At the beam bottom flange, the backing shall be removed. At the top
> flange, removing the backing is optional. (continuous attachment to
> the column with a fillet weld is required) My opinion is that leaving
> backing bars in place is a poor idea, however, it is often cost
> prohibitive to remove them, backgouge and backweld with a reinforcing
> fillet.
>
> ----- Original Message -----
> From: "Gautam Manandhar"
> To: seaint@seaint.org
> Subject: RE: Backing bar in RBS steel moment connection
> Date: Mon, 7 May 2007 14:55:31 -0700
>
>List members:
>
>In a RBS steel moment connection, the expected plastic hinge is at the
>reduced beam section. How important is it to remove the backing bar at
>the beam-column connection? I am aware that in the pre-Northridge,
>fracture initiated at the bottom CJP joint. Is anyone aware of tests
>done with the backing bar in place.
>
>Gautam
>
>
>
>Bart Needham, SE
>Principal, nbse associates, inc.
>Office 206-780-6822
>Office 805-452-8152
>Fax 206-780-6683
>Fax 208-693-3667
>Mobile 206-300-2346
>
>Office locations:
>629 State Street #230
>Santa Barbara, CA 93101
>
>205 Fairview Lane
>Suite 100
>Paso Robles, CA 93446
>
>365 Ericksen Ave. NE
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>Bainbridge Island, WA 98110
>
>Mail and Deliveries:
>321 High School Rd. NE
>Suite D-3 PMB 216
>Bainbridge Island, WA 98110
>
>
>
>
>Bart Needham, SE
>Principal, nbse associates, inc.
>Office 206-780-6822
>Office 805-452-8152
>Fax 206-780-6683
>Fax 208-693-3667
>Mobile 206-300-2346
>
>Office locations:
>629 State Street #230
>Santa Barbara, CA 93101
>
>205 Fairview Lane
>Suite 100
>Paso Robles, CA 93446
>
>365 Ericksen Ave. NE
>Suite 328
>Bainbridge Island, WA 98110
>
>Mail and Deliveries:
>321 High School Rd. NE
>Suite D-3 PMB 216
>Bainbridge Island, WA 98110
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