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Nonstructural Components - how far to carry Fp?

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I have a project where we will be adding some rooftop generators to a 17-story building.   The generators weigh approx 10k each, are approx 11ft L x 5 ft W x 7 ft H, and will be mounted on isolators.  Ip = 1.5.  SDS = 0.526


The new generators will be installed in a rooftop area that formerly housed some cooling towers.  The cooling towers were mounted on a pair of concrete curbs (10” wide x 30” tall x 60 feet long, 13’-6” apart, with transverse 8” x 24”  “fins” at each beam line 6’-8”cc).  The curbs were left intact after the cooling towers were removed.   I figured we could add some new wide-flange beams to span across the existing concrete curbs, bolt the generators to the (n) beams, and bolt the (n) beams to the (e) curbs.  The way I see it, I need to design/check the following items for the elevated Fp force per 2006 IBC Chapter 13:


  1. Anchorage of generator to (n) steel beams
  2. Check (n) steel beams for Fp-level forces due to generators anchorage (including T/C couple due to OT)
  3. Anchorage of (n) steel beams to (e) concrete curbs.
  4. Anchorage of (e) conc curb to roof structure (vert bars welded to bms)


Do you think I need to take my Fp check farther than the above-noted path? (i.e., check existing roof beams for elevated Fp force?)  Chapter 13 is named “Seismic Design Requirements for Nonstructural Components”, and I can’t seem to find any code language regarding how far to carry out the load-path check at Fp force levels.  It seems logical that the “Nonstructural Component” part ends at the anchorage of the curb to the structure…i.e., don’t need to check (e) roof bm for elevated Fp force….but I’m curious to see what others think…


Diane C. Gould, S.E.

Sacramento, CA