How is thermal movement calculated?

Thermal movement is ΔL = α·L·ΔT, where α is the coefficient of thermal expansion, L the member length from the point of fixity, and ΔT the design temperature range.

What temperature range applies in cold climates?

AASHTO LRFD Procedure A specifies a steel range of −30 °F to 120 °F for a cold climate, a 150 °F swing, with concrete and timber over narrower ranges.

Thermal Movement

AASHTO §3.12 Preliminary estimate

Thermal expansion and contraction of a structural member — total movement over the design temperature range, and the expansion/contraction split about an installation temperature.

Results update as you type. These are educational estimates — confirm against the governing code and a licensed engineer before design use.

Method & references

Thermal expansion and contraction of a member of length L over a design temperature range:

ΔL = α · L · ΔT

α — coefficient of thermal expansion (1/°F)
L — expansion length, measured from the point of fixity (ft)
ΔT — design temperature range T_max − T_min (°F)

Cold-region design hinges on this number: AASHTO LRFD Procedure A (Table 3.12.2.1-1) gives a steel temperature range of −30 °F to 120 °F in a cold climate — a 150 °F swing that drives bridge joint and bearing sizing. Entering an installation temperature splits the total into expansion above and contraction below the set temperature.

Reference: AASHTO LRFD §3.12.2 (Procedure A). Coefficients are typical design values; confirm α for the specific material and the governing temperature range for your site.