TM 5-852-4/AFM 88-19, Chap. 4
U. S. Army Corps of Engineers
Figure 4-9. Effect of heated structure size on depth and rate of thaw.
building floor temperature and 32 F.
Rv =
d
=
8
+
4
+
6
(a) Example: Estimate the depth of
k
(12) (1.0) (12) (0.033)
(12) (1.0)
thaw after a period of one year for a building floor
= 11.2 ft hr F/Btu
2
consisting of 8 inches of concrete, 4 inches of cellular
The average volumetric heat capacity of the floor system
glass insulation, and 6 inches of concrete, placed directly
is
on a 5-feetthick sand pad overlying permanently frozen
silt for the following conditions:
(30) (8) + (1.5) (4) + (30) (6)
Cf
Mean annual temperature (MAT), 20 F.
8+4+6
Building floor temperature, 65 F.
3
Sand pad: Dry unit weight γ d = 72 lb/ft , w = 45
3
=23.7 Btu/ft F
percent.
The solution to this problem (table 4-2) predicts a total
Concrete: Coefficient of thermal conductivity, K =
thaw depth of 7.8 feet. This solution did not consider
1.0 Btu/ft hr F; Volumetric heat capacity, C = 30
3
edge effects; i.e., a long narrow building will have less
Btu/ft F.
Insulation: K = 0.033 Btu/ft hr F, C = 1.5
depth of thaw than a square building with the same floor
area because of the difference in lateral heat flow.
Btu/ft F.
3
(b) Figures 4-3, 4-10, 4-11 and 4-12a
The resistances of the three floor layers are in
show measured rates of thaw beneath buildings placed
series, and the floor resistance Rf is the sum of
direct-
the three layer resistances (d = thickness of
layer in feet).
4-16
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