Understanding Railway Rail Sections and Their Rigidity

Railway rail sections are designed in various shapes to support train loads and provide a smooth running surface. These shapes significantly impact their ability to resist different forces, particularly lateral (sideways) and vertical (downward) forces, which directly relate to their rigidity and stiffness.

Let's examine the characteristics of the rail types mentioned:

Flat Footed Rail Rigidity

• Shape: This is the most commonly used rail section worldwide. It has a broad base (or foot), a web, and a head. The base is significantly wider than the head.
• Rigidity and Stiffness: The broad base provides excellent stability against lateral forces without requiring chairs for support. It can be directly fastened to sleepers using spikes, bolts, or clips. This broad base contributes significantly to its rigidity and stiffness, making it highly effective in resisting both vertical loads and lateral thrusts from trains, especially on curves. Its design allows the bending stresses caused by vertical loads to be efficiently distributed.

Bull Headed Rail Characteristics

• Shape: This rail has a head and a foot of similar, but not identical, size and shape, connected by a web. The foot is smaller than the head.
• Support: Unlike the flat-footed rail, the bull-headed rail requires cast-iron chairs and keys to hold it in place on the sleepers. The foot sits in the chair, and a key wedges the rail tightly against the chair jaw.
• Rigidity: While relatively rigid, its rigidity and resistance to lateral forces are less inherent in the rail section itself compared to the flat-footed rail because it relies heavily on the chairs for lateral restraint.

Double Headed Rail Design

• Shape: This is an older type of rail with two identical heads, one at the top and one at the bottom, connected by a web.
• Original Idea: The original idea was that the rail could be inverted and reused once the top head wore out.
• Practical Issues and Rigidity: In practice, this didn't work well because the chairs supporting the rail foot caused wear and indentation, making the inverted head unsuitable for use. Like bull-headed rails, they also require chairs. Due to their symmetrical design which isn't optimized for lateral stability from the section shape itself, they generally offer less rigidity and stiffness against lateral forces compared to flat-footed rails. This type is now largely obsolete.

Butt Headed Rail Context

The term "Butt headed rail" does not typically refer to a standard rail cross-section shape affecting its rigidity or stiffness in the same way as the others. It might potentially relate to a specific joint type or a historical term not widely used in modern railway engineering texts concerning cross-sectional stiffness properties.

Conclusion on Rail Section Rigidity

Comparing the standard rail sections, the flat-footed rail's design with a wide base provides inherent stability and significantly better rigidity and stiffness to effectively resist both lateral and vertical forces compared to bull-headed and double-headed rails, which depend more on external supports (chairs) for stability and are less efficient in distributing stresses due to lateral forces.

Therefore, the flat-footed rail section demonstrates superior rigidity and stiffness for resisting lateral and vertical forces.