6 FACILITY MONITORING
RMS spectra. The curves labeled VC-A through
VC-G in Table 1 have been the standard until
recently when VC-H to VC-M were introduced for
evaluation purposes.
Peak values per frequency from below 1 Hz to 80
Hz are common for micro-vibration measurements.
The third-octave band smoothing and RMS averaging reduce the magnitude of peak values, so care
should be given when referring to data treated this
way. All data should have complete indications of
the metric used and any filtering applied. Whether
amplitudes are presented as velocity in μin/s or μm/s,
or as acceleration in g (gravity), μin/s², or μm/s² will
depend on the project, client, and purpose.
Ground-borne vibrations are generally measured
at or below the ground surface. The measured unit
magnitudes are reported as peak particle velocity
(PPV) in in/s, or mm/s. Building vibrations are
measured with tri-axial accelerometers anchored
directly to building structures such as façade
masonry, foundations, or structural columns. The
measured unit magnitude provided by accelerome-
ters is acceleration in g where 1 g= 9.08665 m/s² or
386.1 in/s².
Design considerations
Localization of buildings away from known exterior
noise and vibration is possibly the most effective
first step. Increasing the weight of the building shell
or core can influence the reaction to ground-borne
vibrations in a positive way. Increasing the floor
slab/column stiffness of each level with MVSE labs
is also a common strategy.
Locally, under each MVSE unit, vibration isolation strategies can combine passive and active technologies to achieve the criteria recommended by the
A visual representation
of the given Vibration
Criterion. Image:
Metropolitan Acoustics
Sound pressures,
vibration amplitudes, and
temperature changes can
impart major impacts
on the functionality
and image definition
of very high-resolution
equipment such as laser-based interferometers,
scanning probe
microscopes, scanning
electron microscopes
(pictured), transmission
electron microscopes, and
photolithography.
Image: Shutterstock
