WHAT
IS DAMPING?
"Structural Damping" refers to the removal of
vibration-related mechanical energy from a structure. This usually
involves conversion of kinetic and strain energy into heat.
A structural beam, floor or wall that is deflected stores a certain
amount of strain energy that is greater for greater deflection. If the
force that is responsible for the deflection is removed suddenly, the
structure begins to move with increasing velocity, converting increasing
amounts of it's strain energy into kinetic energy; when no more strain
energy is available, the structures velocity is reduced and kinetic
energy is again converted into strain energy. This cyclic back and forth
conversion of energy would be repeated continuously-and the structure
would vibrate forever in absence of any externally applied forces - if
it were not for energy being removed by structural damping .
Damping in practical structures can be achieved using several
techniques.
Most common are:
- energy dissipation processes within the structural materials
(primarily on the molecular and grain level).
- mechanical friction (e.g., at structural joints, cracks or
interfaces).
IMPROVING DAMPING
A structure having lower Q values has better damping characteristics.
Standard concrete ranges between 120-200. CONCREDAMP can be designed
with Q values ranging from 30-50 depending on construction requirements.
The damping value "Q" of a structure is measured by locating
the frquency of a Resonance Peak and the frequencies of the half power
point.
The damping of concrete with CONCREDAMP varies somewhat with
temperature. At 90°F, the damping values are about 30% greater than
tabulated 75% values; At 60°F, they are 30% lower.
|
DAMPING
CHARACTER |
"Q" |
Gallons
per
CU. Yd. |
Sacks
of cement per
CU. Yd. |
STRENGTH
PSI |
| Normal
Concrete
|
200
|
none
|
5-6
|
3000-5000
|
| Low
Damping
|
70-100
|
2
to 5
|
6
|
3000-5000
|
| Medium
Damping
|
50-70
|
5
to 10
|
7
|
3000-4000
|
| High
Damping
|
30-50
|
10
to 15
|
8
|
3000-4000
|
| Very
High Damping
|
10-30
|
15
to 20
|
9
|
2500-4000
|
REDUCING RADON BY DECREASING PERMEABILITY
CONCREDAMP decreases permeability in foundations reducing the possible
paths for radon gas infiltration
A consequence of reducing the water content by 50% of the additive
quantity of CONCREDAMP is the increase of the density of the CONCREDAMP proportionately. Increased density further decreases permeability.
The CONCREDAMP elastomer formula uses a polymer and liquid gum to create
a barrier throughout the concrete. This deters chloride penetration and
reduces the chance of rebar corrosion. This same barrier can reduce or
eliminate Radon Gas infiltration.
In consideration of the above, particularly in reference to Radon Gas
and the lack of appropriate alternatives, the implementation of
CONCREDAMP is recommended to deter entry of the gas through foundations.
|
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