Where,
The temperature of the aluminum framing is a major factor determining
thermal movement. Consider the two extreme environmental
conditions within the same year in a major metropolitan city like
Boston5: the coldest day of the year with very heavy cloud overcast
(10°F in January 2017) and the hottest day of the year with no clouds
(95°F in June 2017). “The sunlight is putting energy into the metal.
If it receives energy faster than it can radiate/convect/conduct it
away, its temperature will increase. Ein−Eout=Eaccumulated (which
is a simplified form of the general conservation equation; greater
accumulated energy means greater temperature in this case).”
This accounts for the fact that the temperature of aluminum can
be significant when subjected to sunlight, e.g. 248°F. “In 25°C still,
dry air, the metal can get up to about 120°C in direct sunlight.6”
Remember that 25°C is only 77°F, not the maximum temperature
differential of 85°F in the preceding example that would further
increase the ΔL result.
ASTM E2307 requires the system to be tested for movement by
conducting a movement cycling test. The issue of joint movement
was discussed in a 1990 article written about joint systems in elevated
concrete slabs in buildings to inform the industry that proper joint
and joint system specifications are critical to the building’s functional
reliability.