KEVOS® MAKEOS · Engineering
Expansion Gap Plan (Movement over the Temperature Range, Gap at Installation, Restrained Stress)
For a rail, beam, pipe or panel run that must move with temperature, what gap should I set when installing, will it stay within the joint’s range, and what stress would build up if the gap closed?
Plan of an expansion gap for a run fixed at one end: the length change over the temperature range from the expansion coefficient, the gap to set at the installation temperature so a least gap remains at the hottest temperature, the gap at the coldest temperature, the number of gaps needed if the range is too wide for one joint, and the thermal stress and force that would build up if the run were fully restrained (as the thermal stress tool).
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Length free to move to the gap | m | Length of the run between its fixed point and the gap. |
| Expansion coefficient | µm/(m·K) | Linear expansion coefficient of the material (steel about 12, aluminium about 23). |
| Lowest service temperature | °C | Lowest temperature the run reaches. |
| Highest service temperature | °C | Highest temperature the run reaches (sun on dark surfaces can be well above air temperature). |
| Installation temperature | °C | Temperature of the run when the gap is set. |
| Least gap at the hottest | mm | Smallest gap to leave at the hottest temperature. |
| Largest gap the joint allows | mm | Largest gap the joint, rail or cover plate can bridge. |
| If fully restrained | ||
| Elastic modulus | GPa | Elastic modulus. |
| Cross-section area | mm² | Cross-section area of the run. |
| Yield strength | MPa | Yield strength of the material. |
Method and formulas
- Length change = α L ΔT.
- Gap to set = least gap + α L (T_max − T_install); gap when coldest = gap to set + α L (T_install − T_min).
- Gaps needed = ⌈α L (T_max − T_min) ÷ (largest − least gap)⌉; restrained stress = E α (T_max − T_install) and force = stress × area (as the thermal stress tool).
- Example: set a 11 mm gap at 20 °C; it opens to 20 mm when coldest; restrained, the run would see 60 MPa.
Limitations
- Uniform temperature along the run and free sliding; friction at supports takes up part of the movement.
- One fixed point per run; runs fixed at both ends need the joint in between to take both movements.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Set gaps for crane or conveyor rails
- Plan expansion joints in long cladding or pipe runs
- See the stress if a gap closes
Who it is for
- Site engineers
- Maintenance engineers
- Design engineers
What you get
- Movement over the range
- Gap to set and gap when coldest
- Gaps needed and restrained stress
Interpreting the result
- Setting the gap for the temperature on the day of installation is what keeps the joint inside its range in summer and winter.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 375–376, 578. Topic reference; no source tables or recommended settings are reproduced.
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