gusset plate design

huangyhg

gusset plate design
folks,
please see attachment calculations and also see attached aisc calcs.
the aisc method used ufm case iii modified and gives results that are slightly different. i know the end result would be 4/16 = 1/4" weld, but there could be a case where the result might be choosing 1/4 vs 5/16.
can anyone shed some light into it and tell me if i am doing something incorrectly?
thanks
aisc design example
you're applying eccentricity to the weld.  the aisc example is not, since the weld is concentric to the brace work lines.  see page 5 in the example.
nutte,
could you please explain?
am i incorrect in applying an eccentricity? the workpoint is at the center of the beam and not at the center of the gusset.
i am fairly new to the ufm method and i would much appreciate it if you could help me understand why there is no eccentricity?
thanks
a very stupid question i suppose:
should'nt the alpha calculation be based on an angle of 42 degrees instead of 48 degrees.
did you look at page 5 in the aisc example?  since half of the weld on each side is concentric to the work line, there is no eccentricity.  the horizontal component will be eccentric by half the beam depth.  the vertical component will be eccentric by whatever the distance is from the center of that portion of the weld to the work line.  these moments will cancel each other out, resulting in zero moment on the weld.
@nutte,
in my calculations (first attachment), i am calculating a moment because i am computing the forces at the workpoint and then moving it down to the gusset interface.
there is no net vertical force on the gusset plate. only a horizontal force and a moment.
did you look at page 5 in the aisc example?
yes, i did. i understand the forces are directly computed at the gusset interface.
i will need to spend more time to understand the nuances of the ufm.
thanks for your help. i will need to figure out the difference in results even though i am choosing the same workpoint.
this isn't really the ufm.  the wording in the example describes it pretty clearly.  half of the weld is checked for each brace force.  this portion of the weld is centered on the brace workline, so there is no eccentricity.