Golvet vibrerar av grannens fotsteg

FROTH-PAK är ett bärbart två komponents polyuretansprayskumkit som gör det möjligt för proffs att framställa polyuretanskum av exceptionellt hög kvalitet, snabbt och enkelt, varhelst och närhelst det krävs. FROTH-PAK är avsett att användas som ett tätningsmedel som skummas på plats för luftläckagekontroll och isolering av luckor, sprickor, hålrum och skarvar i klimatskalet. Det används för att täta ledningar, krökar, ventiler, tees och lådor, samt ersättande eller reparerande isolering i kylda behållare och kyllager. FROTH-PAK används runt dörrar och fönsters omkrets, tak-/väggkorsningar, samt tätning av mekaniska-, elektriska- och VVS-genomföringar i väggar, golv, innertak, vindar och tak.

The main factor underlying most vibration
problems is resonance, which occurs when
a load is exerted on a floor at a particular
frequency. For example, a group of people
dancing applies a cyclic force (their footsteps)
to the floor at the frequency corresponding
to the beat of the music (see Figure 1). The
cyclic force produces a maximum floor
acceleration, which depends on the ratio of
the natural frequency of the floor structure
to the cyclic frequency of the applied force
(see Figure 2). When the natural frequency
of the floor coincides with, or is close to,
the forcing frequency, resonance occurs and
the consequences are most severe. During
each cycle of loading, more energy is fed
into the system and the magnitude of vibration
grows, until a maximum is reached.
This maximum is dependent on the amount
of damping in the floor.
During any rhythmic activity, people
apply repeated forces to the floor, ranging
from 2 to 3 Hz. (This frequency is known as
the step frequency). For dancing, resonance
occurs if the natural frequency of the floor
is between 2 and 3 Hz.
If the repeated force has an impact component,
as is the case for aerobics in which everyone
jumps at the same time (see Figure 1),
then resonance can occur not only at the
step frequency, but also at multiples, or harmonics,
of this frequency. For example, an
aerobics class jumping to a beat of 2.5 Hz
(the step frequency) will produce harmonic
vibrations at multiples of 2.5 Hz — i.e., at
2.5 Hz (first harmonic), 5 Hz (second harmonic),
and 7.5 Hz (third harmonic). Since
the natural frequencies of most floors are
greater than 3 Hz (they often fall between
4 Hz and 8 Hz), problems are most likely to
occur as a result of the second and third harmonics.
However, the lower the harmonic the
larger the vibration produced by resonance.

Vibration
can usually be controlled by stiffening the floor
structure, although sometimes the problems
can be addressed by adding damping or by
isolating equipment.