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Seismic  Analysis

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 machinery manufacturer can provide remediation measures. We can measure and report 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.

    Economics (construction costs and isolation/snubber installation labor and maintenance) usually drive the ultimate remediation.

Last updated 25-Agust, 2013
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