Hi John,
I interpret that the referral in 2.17.1 to one sided "groove welds made from one side without backing" is meant towards pjp, which is prequalified (3.3), but prohibited on nontubular cyclic loads unless it can be applied to either (1) secondary or nonstress carrying members, or (2) corner joints parallel to the direction of calculated stress..., as indicated in 2.17.1.
However, I think the referral to "made with backing other than steel, that has not been qualified in conformance with Section 4" indicates that if a different backing, such as copper or ceramics is used, and is applied to a nontubular connection in a cyclically loaded condition, and its application is for something other than (1) secondary or nonstress carrying members, or (2) corner joints parallel to the direction of calculated stress..., as described in 2.17.1, it is not prequalified, and therefore is subject to the requirements and qualification tests in Section 4.
After I finished with the above response, I looked back to my D1.1 2002 code and saw that all the words in paragraph 2.17.1 were underlined, which indicates changes from the previous code.
Then I looked at D1.1 2000 and found that Prohibited Joints and Welds were in 2.27, which states the following in 2.27.2 with regard to one sided groove welds:
Groove welds, made from one side only, are prohibited, if the welds are made:
(1) without any backing
(2) with backing, other than steel, that has not been qualified in accordance with section 4.
These prohibitions for groove welds made from one side only shall not apply to the following:
(a) Secondary or nonstress carrying members and shoes or other nonstressed appurtenances, and
(b) Corner joints parallel to the direction of calculated stress, between components of built up members designed primarily for axial stress.
I think that in D1.1 2004, in 2.17.1, the statement “made with backing other than steel, that has not been qualified in conformance with Section 4" is what's confusing. If you go back to the D1.1 2000 code, to 2.27.2, item (2), it is more clear and precise.
The groove welds that are prohibited by 2.17 do not perform well under cyclic loading, but are permitted in other applications. The exceptions indicated in 2.17.1 items (1) and (2) are because welds in secondary members are not subjected to cyclic stresses, however for loads subjected to cyclic activity, the unwelded side constitutes a stress raiser significance when fatigue loads are applied transversely to the joint, which is why it is imperative to remove backing in these applications.