Define the reference length
Use the continuous member or rail length whose free movement you want to compare.
CRANE & SITE / TOOL 25
Rail & Structure Thermal Expansion Calculator
Estimate the free length change of a rail or steel member between two uniform material temperatures.
Before you start: required inputs
- Measure the assessed length at the initial condition.
- Determine the initial and final material temperatures and the expansion coefficient for the actual material and temperature range.
Calculation diagram
A PRACTICAL WALKTHROUGH
How to use this calculator
Calculate temperature change
Subtract initial material temperature from final material temperature. Cooling therefore has a negative value.
Read the signed movement
Positive millimetres mean expansion; negative millimetres mean contraction. Compare this free movement with the actual restraint and joint layout separately.
100 m steel rail heated by 40 °C
THE INPUTS
100 m initial length, +40 °C temperature change and a coefficient of 12 × 10⁻⁶/°C.
THE RESULT
Free expansion is 48 mm and final free length is 100.048 m.
What does the result mean?
01
The result is free movement of an unrestrained member.
02
Restraints can convert movement into force; this tool does not calculate that force.
03
The illustrative steel coefficient should be replaced when the actual material or temperature range requires another value.
Watch for this
Using the final temperature itself as the temperature change instead of subtracting the initial temperature.
Formula & model conditions +
ΔL = α L ΔT
A negative ΔL means free contraction.
- Uniform temperature change and an unrestrained member with a constant expansion coefficient.
- Temperature is the material temperature. Restraint force, thermal buckling, joints and temperature gradients are not calculated.
Common questions
Should I use air temperature or steel temperature?
Use material temperature. Sun exposure and other conditions can make rail or steel temperature differ from air temperature.
Does this determine the expansion-joint gap?
It gives a free-movement component. Joint position, anchorage, installation temperature and permissible movements still need to be assessed.