The selection of a sliding surface material for bridge bearings is critical due to the frictional forces it generates, affecting the bearings and the bridge’s substructure. Polytetrafluoroethylene (PTFE), alongside lubricated bronze, is a common choice for this purpose.
PTFE, a fluorocarbon polymer, boasts excellent chemical resistance and operates effectively across a wide temperature range. Its standout feature, however, is its exceptionally low coefficient of friction, the lowest among solids, and it operates without stick-slip movement (as noted by David J. Lee). This coefficient further decreases with increasing compressive stress, making it ideal for bearing applications.
However, PTFE isn’t without its drawbacks. It exhibits high thermal expansion and relatively low compressive strength, necessitating careful consideration in design. To compensate, stainless steel plates are often used as complementary contact surfaces. These plates, intentionally larger than the PTFE surface, allow for movement without exposing the PTFE to potential damage. Furthermore, placing the stainless steel plate on top of the PTFE helps protect it from contamination.
In some cases, lubricants are introduced to further reduce friction between the PTFE and stainless steel surfaces. To prevent the lubricant from being squeezed out during repeated movement, the PTFE surface may be designed with dimples. This ensures consistent lubrication and optimal performance over time.
In conclusion, PTFE’s unique properties, particularly its low friction coefficient, make it a compelling choice for sliding bearings in bridge construction. Despite its limitations, careful design and complementary materials can effectively mitigate these challenges, ensuring the long-term functionality and structural integrity of the bridge.