Why Don’t Railroads Need Expansion Joints? — Veritasium

Quick Overview

Key Takeaway: Railroads do not require expansion joints because their continuous welded rails are engineered to withstand extreme thermal stresses by being held in a constant state of tension or compression, preventing buckling or separation.

Key Points: Railroads do not need expansion joints because they are designed to be in a state of constant stress, either in tension or compression, which prevents buckling or pulling apart. Continuous Welded Rail (CWR) is installed at a 'neutral temperature' where it experiences no thermal stress, typically around 90 degrees Fahrenheit. When temperatures deviate from the neutral temperature, the rail experiences significant forces, but these forces are contained within the rail itself due to its immense stiffness and the surrounding ballast. The rail's resistance to buckling is significantly increased by the lateral resistance provided by the ties and ballast, which are designed to hold the rail firmly in place.

Summary

Railroads do not use expansion joints because their tracks are constructed with Continuous Welded Rail (CWR), a system designed to manage thermal expansion and contraction through internal stress rather than physical movement. When CWR is laid, it is done so at a specific 'neutral temperature,' typically around 90 degrees Fahrenheit, at which point the rail experiences no thermal stress. As temperatures rise above this neutral point, the rail attempts to expand, but it is rigidly held in place by the ties and ballast, causing immense compressive forces to build up within the rail. Conversely, when temperatures drop below the neutral temperature, tensile forces develop as the rail attempts to contract.

These internal forces, which can amount to hundreds of thousands of pounds over a mile of track, are contained by the sheer stiffness of the steel rail and the significant lateral resistance provided by the surrounding track structure. The ties and ballast are crucial in preventing the rail from buckling under compression or pulling apart under tension. This method is a more robust and maintenance-efficient solution than incorporating numerous expansion joints, which would introduce weak points and require constant upkeep across the vast lengths of railway lines. The design ensures the track remains stable and functional under a wide range of environmental conditions by keeping the rail in a controlled state of tension or compression.