Backer bar HSS

MegaStructures · May 18, 2021

Does anybody have experience specifying a CJP weld for HSS with a backer bar and can share some of the details of the design? The first thought for the backer is to bend plate to fit the inside of the HSS where a readily available HSS size is not available.

Yes, I do know that using CJP welds is not preferred and would be expensive. When connecting HSS branches in a space truss it's not possible to fillet weld all-around due to the obtuse angles of the HSS faces and for thin tubes a PJP weld is not possible.

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dauwerda · May 18, 2021

Yes, the first choice is often using another HSS that fits inside the HSS being welded. When this is not an option, generally two plates are bent that form "C's", with their outside radius matching the inside radius of the HSS. The two pieces of backer also need to be welded together with a CJP weld if you are following AWS D1.1

sbisteel · May 18, 2021

We've done 3 options:

1.) (2) Bent 1/4" thick plates into C shapes. AWS D1.1 allows them to be discontinuous with a few caveats (10.22.1).
2.) Inset HSS piece.
3.) Thick plate cut to fit inside the opening, like an internal stiffener plate.

Each of those have their pluses and minuses.

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Backer bar HSS

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