Dynamic Stiffness of the Fastening System and Track Vibration Control
- What is the definition of the dynamic stiffness of the fastening system? What is the unit?
Dynamic stiffness refers to the ratio of the dynamic force generated by the fastening system to the corresponding displacement under alternating loads, reflecting its ability to resist dynamic deformation. The unit is kN/mm. A larger value indicates a stronger ability to resist vibration deformation but a worse shock absorption effect; a too small value leads to insufficient track stability and prone to excessive displacement.
- What are the different requirements for the dynamic stiffness of the fastening system in different lines?
High-speed railways require a dynamic stiffness of 30-50kN/mm, which can control the track vibration amplitude within 0.3mm while ensuring sufficient stability; heavy-haul railways need higher dynamic stiffness (50-70kN/mm) to resist deformation under large loads; urban rail transit focuses on shock absorption, with dynamic stiffness controlled at 20-40kN/mm to reduce noise from vibration transmitted to surrounding buildings.
- What factors affect the dynamic stiffness of the fastening system?
The elastic modulus of the elastic clip is a major factor. The higher the elastic modulus, the greater the dynamic stiffness; the hardness and thickness of the under-rail pad have a significant impact. An increase in hardness by 10 degrees increases dynamic stiffness by about 15%, and an increase in thickness by 5mm reduces dynamic stiffness by 10%-20%; excessive bolt preload increases system rigidity and dynamic stiffness, and vice versa.
- How to test the dynamic stiffness of the fastening system?
Use a dynamic stiffness testing system to apply a sinusoidal alternating load with a frequency of 1-50Hz to the installed fastening system, record force and displacement data at different frequencies, and calculate the dynamic stiffness value. The test must install acceleration sensors on sleepers, rails and pads, analyze vibration transmission characteristics, and ensure that the dynamic stiffness meets design requirements.
- What effects will inappropriate dynamic stiffness have on the track?
High dynamic stiffness will aggravate track vibration, accelerate wear of rails and wheel sets, and transmit vibration to the ballast, accelerating ballast compaction by 30%; low dynamic stiffness will cause excessive displacement of the track under load, leading to excessive gauge changes, affecting train running stability, and may even cause rail resonance.