D1.1 Backer Bars
D1.1 Backer Bars
(OP)
Have a building project with CJP field welded flange moment connections where the fabricator is using 2 backer bars one either side of the beam web at the top flange rather than an access hole to allow for a continuous backer bar. I know AWS D1.1 requires continuous backers but the web is acting as a backer and I know a similar procedure (no access hole) is used when welding end plate moment connections. Is there any document exceptions that permit this?
Thanks,
Thanks,





RE: D1.1 Backer Bars
Concerning endplate moment connections...
The removal of the weld access holes was the result of research on the ductility of cyclically loaded connections. Some of the test samples developed cracks in the weld access holes, as deformation of the endplates increased. AISC Design Guide 4 provides a specific welding procedure, and uses a backing weld rather than a backing bar. Even in high seismic applications of field welded flange connections weld access holes are required. And specific detail requirements are given for their geometry and finish.
http://www.FerrellEngineering.com
RE: D1.1 Backer Bars
Is the procedure your fabricator recommends AWS prequalified? D1.1 does require continuous backing or backguoging for CJP welds.
http://www.FerrellEngineering.com
RE: D1.1 Backer Bars
Since I have answered this question a couple of times recently. I asked Duane Miller for his thoughts. Mostly his comments followed my responses above. He had an additional comment that I did not consider. "For the top flange, the access hole not only permits a continuous backing, but it also allows for a "defined" geometry of the groove weld in the center of the flange width."
Hope this helps.
http://www.FerrellEngineering.com
RE: D1.1 Backer Bars
Thanks.
RE: D1.1 Backer Bars
Duane is the chairman of the D1.1 committee, and he did not offer any suggestions to eliminating the continuous backing bar. He also agreed that the weld access holes provide secondary benefit, such as stress relief, in addition to simply allowing access for the backing.
http://www.FerrellEngineering.com
RE: D1.1 Backer Bars
The Design Guide 4, welded endplate without access holes, has a specific welding procedure. The welds are applied in sequence to minimize the residual weld stress. A backing weld is used for the CJP flange weld and a zero root opening is used. And when UT testing is done at the center of the weld (at the web) indications of incomplete fusion are frequently seen. But, ignored based on the overall design of the connection.
But, for field welded connections the shop welding controls are not available. Specifically a root opening is required due to erection and fabrication tolerances. Otherwise PJP welds could be used in the field not requiring backing, etc. with a R = 0. Typically a TC-U4a weld is specified in the field with 30 deg prep and R = 3/8". The beam web is also "set-back". Therefore, in your condition no weld is provided for the length equal at least 2 x k1. (see attached) If the flange force can be transferred with the provided effective weld strength, then your condition should be acceptable. The welds will be concentric so, there should not be any additional bending stresses.
http://www.FerrellEngineering.com
RE: D1.1 Backer Bars
http://www.FerrellEngineering.com
RE: D1.1 Backer Bars
But, still not an option in the field.
http://www.FerrellEngineering.com