Is Weld Access Holes/Beam Copes mandatory?

[cnooc007]

I have several confusions on the use of AWS D1.1,can anyone help me ?


[ul]
[li]Is weld access holes/beam copes on web mandatory ? or as long as the welder can meet the penetration requirement,the fabricator can do the welding without the weld access hole?[/li]
[li]Can i use a CJP WPS(use the same process,parameter...) to weld a PJP weld or filler weld without made a new WPS for PJP welds or filler welds?[/li]
[/ul]

 

[gtaw]

Access holes through the web of a built-up member or a rolled member is to provide sufficient access for the welder to deposit sound weld across the width of the flange. Weld such as that described can be found in moment connections between a column flange and the top and bottom flanges of a beam or girder.

In the case of welding a bottom beam flange to the column flange, the welding is done from the top side in most cases. The welder has to extend the welding electrode through the access hole and progress to the outer free edge of the flange. The backing bar, if used, is typically placed under the groove to support the root bead while it is being deposited.

An alternate to welding the lower beam flange from the top side is to weld it from the bottom side. This is not usually done because of the difficulty in depositing weld in the overhead position. However, there are situations where overhead welding cannot be avoided. In this case the backing bar, if used, is placed on the top side of the lower flange and the backing bar passes through the access hole to provide continuous backing for the full width of the flange.

The attached sketch depicts the two cases I have mentioned in my response. Shown in the sketches are the lower beam flange welded to the column flange. The web connection shown is bolted.

In the event the detailer decides the entire connection should be welded, i.e., the top and bottom flanges welded to the column flange, as well as the web to the column flange, the access hole would still be used to interrupt the weld joining the web to column and the web to beam flanges because it is not a good idea to have welds intersecting at 90 degrees or other angles. The residual stresses resulting from the welding operation are added as vectors. The resultant can easily exceed the ultimate tensile strength of the filler metal, base metal, or both. The concern with residual stresses becomes a greater issue if higher strength steels are involved and when there are more than two intersecting welds. As an example, consider the beam as a built up member where the web is welded to both the upper and lower flanges. Then consider the welding of the lower flange to the column flange. Then consider the beam web welded continuously to the column flange without the use of the access hole. The connection would have three intersecting welds, each perpendicular to the other. Disregarding ductility, because in a practical sense the joint is highly restrained, the resultant force developed because of the three welds will most certainly exceed the UTS of the base metal and the weld if matching filler metal is used. Increasing the strength of the filler metal makes the problem worse. If anything, under matching the strength of the filler metal (relative to the strength of the base metal) would result in the only reasonable hope of preventing a crack from forming.


Consider ASTM A36 welded with E70XX filler metal: The resultant from the residual forces would be on the order of 51 ksi with two intersecting welds.
The resultant force would be on the order of 62 ksi for three intersecting welds, which exceeds the min. UTS or 58 ksi.

If ASTM A992 is used the resultant for two intersecting welds would be 71 ksi and three intersecting welds would be 87 ksi. Both cases exceed the UTS of the base metal (65 ksi min.)

So, as you can see, the assess hole serves several useful purposes.


Best regards - Al

 

[gtaw]

I wasn't able to upload the attachment. Sorry.

I attached it to one of the other sites where you asked the same question.

Best regards - Al

 

[connectegr]

Depending on the intended connection type, the requirements may very. In general a weld access holes is required for flange welded moment connections. In additional to access, weld access holes provide ductility and improved performance of moment connections Also it is impossible to provide complete penetration welds in the center at the beam web. AWS requires continuous backing or backguoging. This area above (or below) the web can cause result in stress risers. For other non-moment connections, this may be allowed. (Not that I would allow it on my projects)

All of this said, research has found that end plate moment connections perform better without weld access holes. Beam flanges are complete penetration welded to the end plate, with an expected partial penetration weld in the area of the beam web. This information is explained in the AISC Design Guide.

http://www.FerrellEngineering.com

 

[dozer]

Gtaw, how do you compute the residual stresses? This is a timely question for me because I had the same question. I was reading the commentary in AWS D1.1 2002, section C2.6.6. It says "Weld access holes are not required nor even desirable for every application." It does go on to say that any transverse joint in the flange of a wide flange would not be considered prequalified.

It sounds like the two responders are soundly against not using access holes for beam to column welded moment connections. Are there any arguments for not using them? A shop guy would say the prep is easier without the access holes but I'm wondering how he would be able to demonstrate full penetration of the flange over the web, never mind the residual stress issue.

 

[connectegr]

The only research I have seen supporting the elimination of weld access holes is with the use of end plate moment connections. Prying of the end plate resulted in secondary stresses in the un-stiffened areas of the flange welds (the access hole areas). These conditions are not simply axial stresses perpendicular to the weld. It was determined that while additional consideration was necessary for the weld located in the area of the beam web, performance was better without access holes. Obviously backgouging is not possible for the entire width of the flange and the weld at the beam web and fillet is considered a partial penetration. An order of welding is prescribed in the AISC Design Guide.

For the reasons listed above and verified by repeated research of CJP welded T joints, weld access holes should be provided.

gtaw maybe be able to provide a more extensive justification. His practical welding experience far exceeds mine.

http://www.FerrellEngineering.com

Providing fabrication and erection efficient structural design of connections. Consulting services for structural welding and bolting.