IBC Collector design

[haynewp]

I have a 2 story building that has eccentrically braced frames through entire length at each story. The frames are stacked. This is seismic category C. I will design the collectors at the roof for the special combinations of 1605.4.

I'm not sure what to do for the second floor collectors. The roof forces will be going directly into the 2nd flr frames from the columns, plus the collectors have to be designed for the 2nd floor seismic force too. But how should this total horiz. load to the 2nd flr collectors be combined (Qe)?

1) Omega x[roof minimum + floor minimum diaph force]
Minimum meaning comparing EQ.16-41 to EQ.16-64 for each
level, using the one that controls in each case.

2) Omega x[floor minimum diaphragm force (16-41 or 16-64)
+ the roof level force from 16-41].

3) Omega x[floor minimum diaphragm force only] + roof force
from 16-41

 

[haynewp]

I discussed this with someone else I work with. I think that as a diaphragm part, the 2nd floor collector horiz force should be checked for H=(F2 or Fpmin)x omega. As a frame member, it should be checked against H=(Froof+F2) without an omega factor.


(Froof and F2=CxV)

 

[haynewp]

On second thought, or third, I think where I have gone wrong in this whole thing is with the definition of a collector. Even though each frame beam will collect the diaphragm force tributary to it's frame, I don't think it is really a "collector" or what the code has in mind for a collector or drag strut. Since the frames are continuous from one end of the bldg to the other, no real "collectors" are present on the roof or floor. Anyone disagree?