Brace Connection Connector Length Warning

Dear Engineer;

The model contains a gusset connection with a HSS brace in tension. In the tension rupture check for the brace, the shear lag parameter U is calculated as 1-x/l, where l = 1". In Table D3.1 of AISC 360-16, l is limited to the H (HSS width), which would be at least 5” in this model. U= 1 should be used when l < H.

Table D3.1 does not address this condition so you will have to rely on your own engineering judgment to modify in the program somehow the length l. The following steel interchange addresses a possible approach that you could use for Case 6. The arrangement might also fall outside the scope of the Specification, and you decide how best to proceed, Read the next: http://msc.aisc.org/globalassets/modern-steel/steel-interchange/2014/032014_si.pdf Carlo Lini, P.E., LEED AP BD+C Staff Engineer American Institute of Steel Construction.

The best approach, I found to solve the issue was considering the next:

1. In the Connection Pad, go to Interfaces/Upper left brace
2. Change in the End connection type to another arrangement as Slotted or some other that allows you to modify the Weld length on brace
3. Chance the length to at least a value equal to the width of the HSS profile that you are using
4. Verify that as soon as you modify the length you can go back to the End connection type and use again the Tee
5. The model is corrected

Attached and image for better approach, Hopefully, this helps you on the solution.

Dear Engineer;

The model contains a gusset connection with a HSS brace in tension. In the tension rupture check for the brace, the shear lag parameter U is calculated as 1-x/l, where l = 1". In Table D3.1 of AISC 360-16, l is limited to the H (HSS width), which would be at least 5” in this model. U= 1 should be used when l < H.

Table D3.1 does not address this condition so you will have to rely on your own engineering judgment to modify in the program somehow the length l. The following steel interchange addresses a possible approach that you could use for Case 6. The arrangement might also fall outside the scope of the Specification, and you decide how best to proceed, Read the next: http://msc.aisc.org/globalassets/modern-steel/steel-interchange/2014/032014_si.pdf Carlo Lini, P.E., LEED AP BD+C Staff Engineer American Institute of Steel Construction.

The best approach, I found to solve the issue was considering the next:

1. In the Connection Pad, go to Interfaces/Upper left brace
2. Change in the End connection type to another arrangement as Slotted or some other that allows you to modify the Weld length on brace
3. Chance the length to at least a value equal to the width of the HSS profile that you are using
4. Verify that as soon as you modify the length you can go back to the End connection type and use again the Tee
5. The model is corrected

Attached and image for better approach, Hopefully, this helps you on the solution.

I don't think U was ever intended to be 1.0 for cases with the weld length L less than the brace nominal size, but rather that condition was to be considered outside the range of applicability because it's a weak connection (U=0 at L=1 7/8"). However, the AISC 2022 Specification Table D3.1 is significantly revised from the 2016 edition and uses a new formula for slotted HSS members. Notice the new formula doesn't have the restriction of "L > H" and will actually not reduce the capacity as much when putting in lengths below H as the previous formula. The new formula with a 5" HSS doesn't reduce to U = zero until L = x_bar = 1.55". L=1" would still be below the new formula limit, but now the formula addresses the full range of potential values from zero capacity to the unreduced capacity.