QUESTION 9
The stress free temperature in a rail in a long section of CWR track is subsequenty on a
hot summer’s day the rail temperature rises to . Calculate the longitudinal forse in the trad.
700 kN compression
1400 kN compression
1400 kN tension
700 kN tension

When dealing with continuous welded rails (CWR), the stress-free temperature is crucial because any deviation from this temperature causes the rails to expand or contract, leading to forces. In your case, we see a significant temperature rise. The longitudinal force can be calculated using the formula:

where is the force in kN, is the cross-sectional area, is the modulus of elasticity, is the coefficient of thermal expansion, and is the change in temperature.

In the context given, the temperature increase is . Depending on the rail type and standard parameters, the typical resulting force in this situation would be in the range you’ve listed, with the correct choice being 1400 kN compression as the rails attempt to push against one another in the heat.

One common mistake is miscalculating the temperature change or overlooking the effects of thermal expansion in the CWR. Many assume the final force will directly translate from the observed temperature change without considering the material properties or geometry of the rails. Always double-check your inputs and ensure you account for all parameters involved.