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Up Topic American Welding Society Services / Technical Standards & Publications / welding symbol for moment connection
- - By emljr (*) Date 09-02-2008 15:03
Seems that here in my design shop everybody has a different opinion for what a single bevel groove with backing bar weld symbol is to look like.
The main designer used 1989 AISC connection book to call out the above weld for a typical beam to beam moment connection.  The catch is that the backing bar symbol has the letter 'M' inside.  I know the intent is to leave the backing bar in place, but I have already gotten feed back that some contractors believe the symbol is asking for the backing bar to be removed using machining process.  I've look through D1.1 and read all the paragraphs concerning leaving the bar in place and the loads & inspection concerns associated with such.
I guess what I am asking (actual cheating here) is, "When did the code stop using the letter M inside the backing bar symbol to denote moment connection, both D1.1 & AISC?  Or is the symbol still used like described above.
I plan to use the RFI process in establishing a clearer weld symbol
Thanks for the help.
Parent - - By bmaas1 (***) Date 09-02-2008 15:34 Edited 09-02-2008 15:42
The "M" inside the backing bar probably denotes the backing bar be made of metal.  An "R" would indicate that it would need to be removed.

Brian
Parent - - By jwright650 (*****) Date 09-02-2008 16:55
Brian, you are correct...an "R" shall be placed in the backing symbol if the backing needs to be removed, the material and dimensions of the backing shall be specified in the tail of the welding symbol (please see A2.4:98 paragraph 4.8 and also Figure 28(A) for reference)
Parent - - By emljr (*) Date 09-02-2008 18:31
Fair enough about the R symbol, but I still am questioning the M symbol.  A senior engineer still thinks it means machine removal of backing.  Of course he went on to tell how much dislike he has for backing bars and the only good use of them is for real thin members other wise stay away from them.  I can see his point specially for corrosion concerns (I am in one of the most corrosive environments, Rocket fuel and ocean spray) and UT readings.  Of course the UT is covered in D1.1 commentary and that is a good read.  I have scoured many books today and have yet to find a clear definition.
Going to keep looking............
Parent - By jwright650 (*****) Date 09-02-2008 18:55
As for whether "machining" is required....refer to A2.43 paragraph 3.13....this "M" is inside the backing symbol and not referenced as described in A2.4 paragraph 3.13. I know well of the AISC manual due to the fact I used that very manual as a structural detailer for many years before getting into QC. I did notice that the 13th edition does not mention or show the "M" in any of the moment details anymore, like the older manual of steel construction did (the green ASD book and previous versions). I simply can not find reference to the "M" inside the backing symbol in anything that i have in my library.....sorry.
Parent - - By jwright650 (*****) Date 09-02-2008 19:00
Please let me know if you find a reference to the meaning of this very elusive "M"...

My gut feeling is sort of that like Brian mentioned...M meaning a Metallic backing vs Ceramic or a non-metallic material
Parent - - By 803056 (*****) Date 09-02-2008 19:04
I have to visit my friendly eye doctor this afternoon. Time to renew my SCWI and update my ACCP certs.

However, I'll check my 2007 edition of A2.4 to see what it says on the subject.

Best regards - Al
Parent - By jwright650 (*****) Date 09-02-2008 19:11
Al, I cannot find it in any of the newer library materials...

it was an older reference...ie 9th edition Manual of Steel Contruction ASD symbol is shown on pages 4-100, 4-127, 4-128, 4-129
Parent - - By hogan (****) Date 09-02-2008 19:41
The "M" in the backing symbol requires metal backing. A "M" above the contour line requires the surface to be machined to required dimension.
Parent - - By swnorris (****) Date 09-02-2008 19:46 Edited 09-02-2008 20:28
emljr,

There has been confusion about this over the years.  D1.1 stopped using "M" inside the backing/spacer symbol several years ago.  When it was used, it was accompanied by "see note", which was located in the tail.  This note, was either shown to be:

M - Material as specified

or

MR - Same as M but removed after welding  

The "M" was simply a designation for backing or spacer.... "M" = steel, or "M" - Material as specified, which had to meet specific D1.1 criteria.  If backing was to be removed, "MR" would be shown inside the backing symbol, indicating the removal of the steel backing.  

Then and now... if welds are required to be mechanically finished, the finishing symbol "M" (machining) is used.  This is where the confusion came in.  This "M" is not shown inside the backing or spacer symbol, but is shown directly over a weld symbol.  This finishing symbol only indicates the method of finishing, not the degree of finishing.

Currently, and previously mentioned, an R is shown inside the backing symbol, indicating removal of backing. 

Also, I'm not sure that "M" was ever an official designation for a welded moment connection.

Edit: Tell your senior engineer to refer to the current A2.4, at 5.12.2, Contours Obtained by Postweld Finishing and look at the finishing designators and how they're used with welding symbols.   
Parent - - By 803056 (*****) Date 09-02-2008 21:11
I just looked through my A2.4-2007. It lists the letter "R", when placed within the symbol for backing, as meaning the backing is to be removed. The material specification and size of the backing is placed in the tail of the welding symbol.

I found nothing using the letters "M" for metallic backing and "C" for ceramic backing.

I did see letters for the method of finishing welds to obtain a specified contour, but the method does not include a requirement for "degree of finishing", i.e., surface roughness. The letters for contour were:
C for chipping, G for grinding, H for hammering, M for machining, P for planishing, R for rolling, and U for unspecified.

Forgive me if there are any typos. I can hardly see. My pupils are the size of my irises and I could hardly see driving back from the optometrist.

Best regards - Al
Parent - - By jwright650 (*****) Date 09-03-2008 00:27
Al,
You just verified that nothing has changed in the AWS Standard for Welding Symbols (A2.4) from the edition that I have.
I need the newer edition for my library, I have to remember to order one before our next audit.

Hope your eyes feel better soon... that is the only part of going to the eye Dr that bothers me. Thank goodness for shade 5 cutting glasses for the ride home...LOL
Parent - By bmaas1 (***) Date 09-03-2008 17:58
I have never seen the "M" as an official designation but have seen it used from time to time throughout my experince at different shops.  It was only used to convey the use of a metal backer.

Brian
Parent - - By ziggy (**) Date 09-04-2008 02:02
This is going to sound stupid, but I have to ask: How does one "machine off" a steel backing bar at a moment connection? I am familiar with "washing off" (oxy-fuel cutting) backing bars, but "machining off?" You lost me.
ziggy
Parent - - By jwright650 (*****) Date 09-04-2008 12:26
There is a hand held "milling machine" of sorts that can be used to remove a backing bar, or machine a cap of a weld flat. I think Heck Industries makes one....You can also use this same machine to prepare nice, square to the flange, bevels as well.
Parent - - By ziggy (**) Date 09-04-2008 15:23
John
We had one of those in our shop but for the life of me it seemed incredibly costly to machine off backing bars. We did use the thing for beveling plate though. Thanks John.
ziggy
Parent - - By jwright650 (*****) Date 09-04-2008 16:04
I agree with you......we typically use the carbon arc gouger to wipe off backing bars and run off tabs. I have never actually seen anyone machine off backing bars before, but i understand that some testing agencies do this before bending welding coupons....but then we are only talking about machining a very small 3/8" piece of backing there.
Parent - - By emljr (*) Date 09-05-2008 18:33
My first impression of the detail was that the type of backing was being called out M = metal.  But the question came from our construction management group and I believe they were trying to head off some future RFI's from bidders.  Wouldn't want FPC's thinking that additional work steps had to be incorporated to remove backing by some exotic method.  Plus when we do the 90% pull for the drawings, didn't want the costomer to get hung up on a small detail, there are bigger details to deal with then whether to remove backing or not and how.
Easy enough solution though....remove the M and let the FPC figure it out.
I appreicate all the help and input.  You guys and gals are reall pros............
JW, I am up for my 9-yr recert  and plan on being at the Miami code clinic in Dec 08.  still have to do the visual acuity my self !!!!
Parent - - By jwright650 (*****) Date 09-05-2008 18:51
[quote]JW, I am up for my 9-yr recert[/quote]

Me too...my 9yrs is almost up.  I have a few months to decide what I'm going to do.
Parent - - By bmaas1 (***) Date 09-05-2008 19:14
I retest for my 9 yr in December.

Brian
Parent - By 803056 (*****) Date 09-07-2008 14:07 Edited 09-07-2008 14:11
Why not go for an endorsement?

Why take a test that you've taken and passed before.

The endorsement will add to your credentials rather than simply maintain the status quo.

If you've passed D1.1 open book examination, consider taking the D1.5 open book, or the API 1104, or ASME just to name a few possible alternatives to taking the Part B test again and again. There are several endorsements that are in the Beta stage of development that might be of interest to those individuals working with structural aluminum, ASME, or structural steel inspection.

Just a thought.

Good luck - Al
Parent - By 3m Date 11-14-2008 16:35
I just had the same connection detail (M in a backing bar opposite a groove weld symbol) for a column to a base plate. I am relatively new to structural steel. My background is in ASME Sec. 1 and 9, B31.1, B31.3. This is the first time I have seen a base plate designed as a FR moment connection. The flanges were cjp and the web called for a 1/4" fillet. I also could not find the "M" in a box in AWS 2.4:2007. I did see a reference to an "M" for a contour. In the 9th ed. of Manual of Steel Construction, 4-127, there is an M in a box, however, I can't find this in the 13th ed., which is the latest ed. and the one we're using. We called the eor and he said, "of course it's a moment connection". I am not the one who spoke to him, because I would have asked him where he found this weld detail with the M. We made a full pen weld with a single bevel from the web to the outside of the flange with weld access holes. We didn't use a backing bar, we ground it and back welded it. Would this be acceptable? Is it assumed that all moment connection welds need to have UT. That is the impression we got from the eor. I usually see this info in the GSN or specs. I did see the following thread concerning weld access holes.

http://www.aws.org/cgi-bin/mwf/topic_show.pl?pid=79364;hl=moment%20connection

Same here...I usually see them as detailed in the top sketch.

However a bit off topic....we are now seeing end plated beam-moment connections with no rat holes. My shop just did 4 of these beams the other day and didn't look closely enough at the dwg and added access holes through the web as they have been doing for many years and when I asked the engineer about this, he made us cut off the end plates plus enough of the beam to get rid of the access holes and weld on thicker end plates to make up the difference. That mistake cost us about 80 man hours to correct that lil boo-boo.

I just retested last june for my 9 year recert.....it didn't seem that difficult if you know your WPS.
Parent - - By rsx-s-02 (*) Date 09-09-2008 15:38
As far as when it happened I can only narrow it down to sometime between the publications of the 8th and 9th edition of the AISC's Manual of steel Construction (1980's to 1990's).  I've even looked through the 6th and 7th editions and found no backer symbol in the 6th and no "M" in the symbol in the 7th.  Also, if you look in the first edition of the "Detailing for Steel Construction" book published by AISC (the red book) on page 6-21 they mention the "M".  It reads: "The weld symbol indicates the requirement for the backing or spacer bar by the symbol "M" within a box which incorporates the usual basic weld symbol characteristics.  This material should be identified and billed on the drawing."  There is also a chart on page 6-15 that shows the backing symbol and spacer symbol to have the "M" within the box.  The second edition of "Detailing for Steel Construction" (the blue book) has removed the "M" from the same chart.  (Figure 4-20 on page 4-24)   I can not find reference to the backing symbol with the letter "M" in the box in any AWS publication.  The letter "R" in the box does indicate removal as stated in previous posts.  Best of luck.  :-)
Parent - - By swnorris (****) Date 09-09-2008 16:22
In my above post dated 9/2, the resources for my comments were taken from past experience, the Eighth Edition of the AISC Steel Construction Manual (used from 1980-1989), and the 1979 edition of A2.4 Symbols for Welding and Nondestructive Testing.
Parent - - By 803056 (*****) Date 09-10-2008 02:23
It's time to update your library. Your welding symbols standard is past voting age!

Best regards - Al ;)
Parent - By swnorris (****) Date 09-10-2008 11:00
Auditors don't like to see 'em because they're concerned that someone will grab an outdated one and use it.  I like to keep the outdated ones just for reference.  They've came in handy more than a few times over the years.  My answer to the initial posting by emljr is a good example.  I also like collect vintage books on drafting, welding, older AISC manuals, Smoley's, management, etc. 
Parent - By welderbrent (*****) Date 11-14-2008 17:00
The only reference I can find to the purpose of the 'M' in the backing bar symbol is in an older copy of "The Procedure Handbook of Arc Welding" put out by Lincoln Electric.  It says "Material and dimensions of backing as specified". and puts a note in the tail of the welding symbol.

Hope that helps.  Have a Great Day,  Brent

And I agree with others posted and don't see why some can't understand that finish symbols are located above not in the bar.
Up Topic American Welding Society Services / Technical Standards & Publications / welding symbol for moment connection

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