Q: How is the holding power of a spike in a wooden sleeper actually generated?
A: The holding power is generated primarily by two forces: Friction and Compression. The driven spike displaces wood fibers, which elastically compress against the shank of the spike. This creates a powerful radial pressure along the entire length of the spike that grips it firmly. The friction between the metal and the compressed wood provides the resistance to pull-out forces.
Q: What is "spike popping" and what causes it?
A: Spike popping is when the head of a previously driven spike rises above the baseplate or sleeper surface. It is often caused by the sleeper wood swelling due to moisture absorption, which pushes the spike upward. It can also be a sign of failed holding power, where traffic vibrations are slowly working the spike loose. Popped spikes must be re-driven or replaced.
Q: Can spikes be used in bridge timber fastening?
A: Yes, specially designed spikes are commonly used to secure guard rails, check rails, and sometimes running rails to timber bridge decks. The principles are similar to track spikes, but the specific spike type and installation pattern are engineered for the unique loads and environmental exposure (often more moisture) found on bridges.
Q: What is the role of a "spike washer" and when is it used?
A: A spike washer is a hardened steel plate with a hole, placed between the spike head and the baseplate or sleeper. It is used when the sleeper wood has become worn or compressed around the spike hole. The washer provides a larger bearing surface, preventing the spike head from pulling through the weakened wood and helping to restore clamping force.
Q: How does freeze-thaw cycling affect spikes and their hold?
A: In cold climates, water that has seeped into the space around a spike can freeze. Ice expansion can exert significant pressure, potentially widening the hole in the wooden sleeper and permanently reducing the spike's grip. Repeated freeze-thaw cycles can progressively loosen spikes, making them a particular maintenance challenge in seasonal climates.