Factors affecting and testing the stiffness of fishplate connections
- What factors affect the connection stiffness of fishplates?
The strength of the fishplate material is the foundation. Fishplates made of high - strength steel (such as Q345) have a connection stiffness 10% - 15% higher than those made of ordinary carbon steel (Q235). Insufficient bolt preload will reduce the connection stiffness, and the stiffness is optimal when the preload reaches 60% - 70% of the bolt yield strength. Insufficient contact area between the fishplate and the rail, such as gaps or wear, will reduce the stiffness. A 10% reduction in contact area may reduce the stiffness by 8% - 12%.
- How to test the connection stiffness of fishplates?
Static loading test is adopted. Symmetric loads are applied at both ends of the rail joint, the relative displacement at the joint is measured, and the stiffness is calculated through the "load - displacement" curve (stiffness = load/displacement). In dynamic testing, a vibration instrument is used to apply sinusoidal loads, and the stiffness values at different frequencies are recorded to evaluate the performance under dynamic forces, which is closer to the actual operating state. During testing, the load direction must be consistent with the rail axis to avoid the influence of additional bending moments on the results.
- What impact does insufficient connection stiffness have on train operation?
Insufficient stiffness leads to large relative displacement at the rail joint, which will cause strong impact when the train passes, increase wheel - rail noise and reduce passenger comfort. Long - term impact will accelerate the wear of rails, fishplates and bolts, shorten their service life, shorten the maintenance cycle by 30% - 50%, and increase railway operation costs.
- What are the differences in connection stiffness among different types of fishplates?
The connection stiffness of double - ended fishplates is usually 70% - 75% of the rail base metal stiffness, suitable for ordinary railways. Oblique joint fishplates have more uniform stress, and their stiffness can reach 80% - 85% of the base metal, suitable for high - speed and heavy - haul railways. Insulated fishplates have a stiffness 5% - 10% lower than that of the same specification steel fishplates due to the insulating layer, but they can meet the needs of electrified railways.
- How to improve the connection stiffness of fishplates?
Select high - strength materials and thickened fishplates. For example, increasing the thickness from 16mm to 20mm can increase the stiffness by 15% - 20%. Ensure that the bolt preload meets the standard, strictly control it with a torque wrench, and retighten it every six months to prevent loosening. Regularly maintain the fishplates, clean the contact surface debris, repair worn parts to ensure close contact, and replace with new fishplates when necessary.