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Built-up steel Section Using Reinforcing Steel

Built-up steel Section Using Reinforcing Steel

Built-up steel Section Using Reinforcing Steel

(OP)
I've been retained to review the design of a canopy structure. The canopy consists of multiple T-Frames (18ft O.C.) with the frames built-up of cold rolled sections; Dbl CEES 16x4x10Ga stitched welded to form a box section. The box section alone does not resist the design forces and thus needs to be reinforced/built-up (approximated design ratio of 1.7). The designer placed 4-#8 bars in each of the inside corners of the CEES by weld using a staggered intermittent (2-24) PJP Flared Grove Weld.

I've asked the designer to provide background information as follows:

1. Allowing intermittent groove welds on Built-up Members (AWS D1.1-15; 2.12)

2. Maximum Spacing of Intermittent Welds shall not exceed 24 times the thinner plate (AWS D1.1-15; 2.12.2)

3. Unpainted weathering steel steel intermittent welds shall not exceed 14 times the thickness of the thinner plate (AWS D1.1-15; 2.12.3)

I received the following response:

1. The use of intermittent PJP groove welds are allowed. See Ssection 2.7.3 of AWS D1./D.1.1M:2004
2. The Section referenced above is 2.11 for Built-up members and not a section for coldformed shapes. No plates were used in this built-up section; therefor, this does not apply
3. Again we are not using plates in are built up member

I would appreciate any comments confirming the above response or refuting comments.

Thanks
Charlie85


RE: Built-up steel Section Using Reinforcing Steel

According to D1.1 scope, you are referred to D1.3. According to D1.3, you are referred to Annex A which requires compliance with D1.3 sections 2.2.3 and 4 regarding flare groove welds. It also requires testing of the weld type per D1.3, sections 4.6.3 (there are to be at least 2 tests and I suggest that you have the round bar - not a plate - welded to inside of the sheet and then fail that assembly with a chisel).

At this point, I strongly recommend one of two things - revise the assembly to something a bit more standard (HSS) or both of you get a copy of AWS D1.3.

Have you looked into compliance with AISI S100?

RE: Built-up steel Section Using Reinforcing Steel

Did they use weldable grade rebar?

RE: Built-up steel Section Using Reinforcing Steel

(OP)
Dear Teguci - Yes, I would prefer a standard section, but cost is the driving factor. A quick preview of D1.3 discussed sheet-to-sheet and Sheet-to-Structural Member Grove Welds with force applied transverse. The actual condition has force applied longitudinally and it appears that D1.3 does not discuss a beam section comprised of multiple shapes (sheets, bars, etc) creating a built up section for resisting bending moment; And whether an intermittent weld is permissible in this situation and if so a minimum spacing.

Dear Lomarandil - Yes, weldable rebar

RE: Built-up steel Section Using Reinforcing Steel

Cost is always a driving factor which is why I recommend a standard section smile. D1.3-2.2.3(2) - "Loads applied longitudinally." Welding bars to gage metal is common when reinforcing OWSJs. SJI Digest 12 should have some details on that but I do not have a copy.

What is the allowable stress being used for the CEE and the bar?

RE: Built-up steel Section Using Reinforcing Steel

Charlie85:
Of course, cost is always an issue..., so then they crap up the design with a bunch of incompatible materials, details and joinery, not knowing a wit about structures and how they really work; and finally ask some willing Structural Engineer to bless their mess and act as the insurer of last resort. Let the “Designer” justify his mess, he made it. I think we really have to learn to turn down the impossible and stupid projects, for a small fee (low cost is important, remember?), the work is all done, can’t you just sign off on it? Buy the way, the design fees already went to that other guy, on the cheap, who isn’t able or qualified to really justify his mess.

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