Vibration testing was conducted by FHA at the site to evaluate vibration
relative to building occupants, using the ANSI Threshold of Perception.
Vibration levels measured on the desks at selected locations exceeded the
ANSI Threshold by about 18 dB re: 1 µm/s RMS.
On-site observation also reviewed that excessively stiff spring hangers
were installed in two of the suspended transfer fans. The situation was worsened by
the use of springs for lateral seismic restraints.
FHA recommended replacing the as-built lateral seismic restraints
(springs) with slack aircraft cables, installing thrust restraints at flexible duct
connections to adjacent ductwork, and in-field inspection of the spring hangers.
Some of the spring hangers were found to be short-circuited upon further inspection.
FHA's recommendations were implemented and subsequent on-site testing
showed vibration levels on the desks of previously tested locations to be at the nominal
ANSI Threshold. No further complaints were reported.