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Physics
Thermal expansion — Bridge joint and bimetal strip
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Change the temperature to explore a bridge expansion joint and the bending of a bimetal strip.
Raise the temperature and watch the gap at the right end.
°C
Reference: 20 °C
m
mm
Steel · length 25 m · gap 12 mm · 60 °C
Gap open
At the reference temperature, the bridge length and gap have their initial values.
Free length change
0.0 mm
How it is calculated
ΔL = αL₀ΔT
ΔT = T − 20 °C
Steel: α = 12 × 10⁻⁶ K⁻¹
Temperature at first contact: 70.0 °C
Outside the temperature range being explored
Model notes
- Temperature is uniform and changes instantly; heat transfer is not simulated. The undeformed reference is 20 °C.
- Constant expansion coefficients: steel 12 × 10⁻⁶ K⁻¹, aluminum 25 × 10⁻⁶ K⁻¹, brass 19 × 10⁻⁶ K⁻¹. These are representative values, not values for every alloy.
- The bridge has one longitudinally fixed end and one sliding end facing a fixed abutment. Once the gap closes, displacement is constrained and blocked expansion is reported. Stress, buckling and damage are not calculated; this is not a bridge design tool.
- The strip is 200 mm long with two 0.5 mm layers; Young's moduli are 200 GPa for steel and 90 GPa for brass. The layers are perfectly bonded, with one end clamped and the other free. Gravity, external loads, layer slip and plastic deformation are ignored; small-strain theory and a circular arc are used.
- The bridge length is shortened in the drawing and its gap is magnified. Strip thickness is enlarged to show both layers, while curvature follows the model. Separate-layer length changes are hypothetical unbonded values, not actual lengths of the bonded layers.