TM 5-852-4/AFM 88-19, Chap. 4
must be established at sufficiently low values to reflect
0.25 percent), and higher carbon steels may be expected
the presence of the surface coating of treatment
to be brittle. Although special alloy steel is not likely to
material. Wood piles which are embedded entirely in
find application in foundation work, it may be noted that
permafrost (capped at the permafrost table) need not be
addition of nickel in the amount of 2-/4 percent will
treated.
ensure satisfactory properties of steel to temperatures of
(2) One of the most important properties
-50F and additional amounts up to 9 percent will
influencing strength of wood, especially at low
increase the range to -320F. Almost all aluminum and
temperatures, is the moisture content.
Table 2-2
titanium alloys can be used at low temperatures (except
presents the relationships of specific gravity and various
high strength aluminum in which stress concentrations
strength properties of wood at room temperature, based
are likely to occur) and essentially all nickel and copper
on average results of tests on a large number of species.
base alloys. However, because the properties of zinc
As illustrated in figure 2-19 compressive strength tests at
and its alloys are adversely affected by low temperature,
44F show higher values at all moisture contents than
brass, a zinc-copper alloy, is unsuitable for low
tests at 68 F with a maximum at approximately 82
temperature use. Parts made from brass have been
159
as shown in
percent. Tests conducted by Kollman
known to shatter under normal handling techniques.
figures 2-20 and 2-21 indicate nearly straight line
Galvanizing has shown cracking and spalling when
increases of compressive strength and toughness ratio
subjected to cold in arctic areas if the coating was too
with decreasing temperatures over a wide range. These
thick.
effects are proportional to density. Experiments at the
(2) Cold embrittlement susceptibility of the
Forest Products Laboratory with Sitka Spruce and
steels used should be known, and the possible effects of
Douglas Fir showed an increase in bending strength of
the temperature extremes and types of loads which will
about 1 to 2 in the cold to room-temperature strength
be experienced during both construction and subsequent
ratio. Figure 2-22a shows the effect of temperature on
operation should be examined. As evidenced by years
the modulus of rupture and modulus of elasticity of three
of experience with mild steels in structures throughout
species of wood tested in flexure and figure 2-22b shows
Alaska, it should not be necessary to use special alloys
the effect of temperature and moisture content on the
in structures and foundations when the number of fatigue
modulus of elasticity of plywood. One of the special
cycles or dynamic stress level is low. However, the
characteristics of wood in the frozen state is that failure
possibility of brittle fracture in either structural
is often sudden, without the usual audible advance
components or construction equipment under other
warning of overloading. Such failure occurs violently with
conditions including the construction phase must always
a loud report and separation of the parts is complete.
be kept in mind.
For example, components of
(3) Wood piles cannot be driven into
excavating equipment often fail when operated at
permafrost by hammer; this may dictate the use of steel
extremely low temperatures unless they are kept heated
instead of wood piles. Wood and steel must both be
or are made of special, higher cost steels.
protected from the possibility of fire damage which is a
(3) Steel piles can be driven successfully
problem of major concern in remote cold areas. (See
into permafrost composed of fine-grained soil (sand, silt
16
TM 5-852-9/AFM 88-19, Chap. 9 .)
or clay) at soil temperatures down to about 25 F. Steel
b. Metals.
The predominant problem
pipe piles, 6 inches in diameter (schedule 80), were
encountered with use of metal in cold regions is cold
driven with a diesel pile hammer to a depth of 21 feet
embrittlement fracture.
Generally speaking, as
into the silt-ice soil at the Kotzebue Air Force Station in
temperature is lowered the hardness, yield strength,
the late winter with soil temperatures approximately as
modulus of elasticity, and endurance limit of most metals
indicated in figure 1-3 for 11 February 1960.
and alloys increase. However, many of these same
Compressed air, diesel and vibratory hammers have
47,48,49,134
. Examination of steel
metals become embrittled at reduced temperatures and
been used successfully,
pipe and H-piles installed for periods of 8-11 years at the
will shatter or fracture when subjected to stresses
U.S. Army CRREL field station at Fairbanks, Alaska,
(especially due to impact) that would be allowable at
showed that the length of pile embedded in permafrost
normal temperatures. Characteristic of this type of
was unaffected by corrosion and only insignificant effects
failure is lack of deformation or prior indication of failure.
183,184
. Protective
were observed in the annual thaw zone
(1) A relatively small group of pure metals
coating of steel in the annual frost zone, therefore, is
remains ductile at low temperature, including nickel,
optional; it may be needed only under special local
copper, aluminum, lead and silver. Several other metals
conditions. Paint or similar protective coatings reduce
such as magnesium, zinc and beryllium are brittle, with
the potential tangential shear which can be developed
little ductility even at room or slightly higher
between frozen soil and pile surfaces and care must be
temperatures. The behavior of ferrous metals covers a
taken that such materials are not applied below the level
very broad range of possibilities. The brittleness of
carbon steels increases with the carbon content (up to
2-27
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