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%20connectionSame 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.