Seismic Design Manual Braced Frame Problem 2

[palves]

I am currently trying to work through an OCBF Design Example and am confused with Example 3.4 on page 3-17.

1. On the "Gusset to Beam Weld Design" I don't see where "fpeak" and "favg" come from. I looked all over and can't find those equations so if somebody could point me to them that would be great.

2. On page 3-16 I'm a little hazy on how exactly they come up with alpha and beta. I understand what those variables theoretically are, but the numbers they put to it don't match what I think it should be in my head. Why subtract 1 from 9 if the gusset plate is directly to the beam? Thanks for any advice.

 

[JAE]

1. It is simple statics. You are trying to determine the actual stresses on the weld lines and these are based on a P/A +/- My/I type calculation. Once you have the x and y stresses, you then use a square-root-of-sum-of-square (SRSS) calc to get the resultant maximum stress on the weld line.

2. They are calculating the length of weld (9" - 1" cope at the corner), then dividing that by 2 to get the center of the weld, then adding back the 1" cope to get the distance from the beam-column corner to the center of the weld line.

 

[palves]

Great, that helps out a lot JAE. Now do you also happen to know where the provision for designing for the greater of "fpeak" or "1.25favg" is called out? I seem to be missing that.

 

[nutte]

The 1.25 factor accounts for the uneven stress distribution along the weld length. It was 1.4 in previous AISC manuals. Look in the 13th edition manual, page 13-11.

 

[palves]

Now I have a new question on the same problem. On pg. 3-18 it checks the gusset plate for rupture and yielding at the beam weld. How come they are able to get away with only checking shear rupture, and then saying that tensile rupture and yielding as well shear yielding will not govern. If I check this out through the equations J4-1 through J4-2 on pg. 16.1-112 of the steel manual I get that shear yielding actually controls the gusset thickness. Any insight?