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Railway track expansion joint: Expansion and contraction of steel and concrete structure due to seasonal heating and cooling is a common problem found in civil engineering. To combat this problem, engineers put expansion joints to absorb these changes.

This problem is compounded on railway tracks. This could lead to rail buckling, known in the industry as “sun kink”, as shown below, and cause the derailment of train. When exposed to temperature variations, the rail tends to vary its length. If this tendency is freely allowed, for a temperature

variance Δt, the rail length L will vary by ΔL. This length variance can be computed as:
ΔL = αLΔt
where α = expansion coefficient of steel
= 11.5 x 10–6 °C.
The coefficient of thermal expansion is defined as the fractional increase in length per unit rise in temperature. Traditional railway tracks are of standard lengths. When the tracks are laid, the lengths are joined end to end using “fishplates”—short lengths of steel plate overlapping the joint, and bolted to the ends of the rails. At each joint there must be a short gap (≈ 1/8") between the rail ends, to allow for longitudinal thermal expansion of the rails on hot days.
Q. What will be the expansion of a 20m long railway steel track for 30°C variation of temperature?