The topic of "Seismic" has three diferent connotations; eartquakes,
buildings and nuclear reactors. These are treated in turn:
Earthquakes: These are natural disasters that generally cannot be
avoided; they must be antcpated. the anticipated building floor
vibration depends on the location of the installation site. Historic
records are compiled into earthquake zones accouding the overall floor
spectrum accelerationamplitudes in vertical, east-west and north-south
directions. The architects and engineers use the specifc zone values
fpr the site. The pertinent accerarion alues are applied to
allstructural design and all installled equipent design (piping and
standing equipment). spring and shock mounted equipment reqire special
handling, as the springs are necessaily sft in normal use, but
ust include stays or "snubbers" to keep the equipment tethers in case a
a real earthquake or similar shake.
Building design: Buildings
exposed to earthquake accelerations can suffer damage to to high walls
and structures; the cmponents within them can be dalaged (unsuported
piping and equipments installed with inaequate contraints.
Safety critcal equpment (nuclear reactors): Installations that pose a
threat to human health if broached require special consideration in the
case of earthquakes and other physical damage. In that case, air
vetilation requires special consideration that depends on their HVAC.
Any inflected damage can result in the release of radioactive gasses
that escape into the nearby atmosphere. Accordingly, a negative static
pressure must be maintained indefinitely. Delivery of the exhast gasses
must occur to filters that remove siad radioactive gasses.
a- We measure the floor
vibrations in structures with a seismic sensor capable of detecting
vibration well below the human sensory threshold, measured in 1/3
octave bands from 1 Hz through 10,000 Hz if necessary, likely to be of
concern for the operation sensitive equipment such as scanning electron
microscopes and magnetic resonance imaging (MRI) devices. Where such
building floor vibrations are greater than the human sensory threshold
(above .001 inches per second RMS) concern is often expressed regarding
residential and office workplace comfort. We often measure greater
vibrations with a small accelerometer, then analyze those data
according to frequency and amplitude, often searching for the vibration
source if not obvious, and recommend mitigation measures.
b- "Balancing" limit criteria,
often expressed - say as 0.05 inches per second or 1 mm/second - for
operating machinery is often used for preventive maintenance or as a
troubleshooting measure. Once identified as being suspect, the
manufacturer can provide remediation measures. We can measure and
such vibrations. Many firms and technicians have vibration meters to
identify these situations. We are often consulted over concern that
these common unbalance vibrations are seriously disturbing nearby
persons or sensitive equipment. We measure these vibrations and their
energy spectrum, relate these to the disturbed entities, and then we
provide remediation measure recommendations such as more vibration
isolation or that preventive maintenance be applied where necessary.
c- Similar to b- We are often
consulted over concern that vibrations from nearby or unknown sources
are seriously disturbing nearby persons or sensitive equipment. We
measure these vibrations, relate them to surrounding entities such as
nearby machinery, or road traffic or rail traffic, and then provide
remediation measure recommendations such as isolation either of the
disturbed entity, or the emitting source such as HVAC machinery.
isolation/snubber installation labor and maintenance) usually drive the
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