Dynamic response and vibration control of fastening system
- What are the main indicators of the dynamic response of the fastening system?
Vibration acceleration is the core indicator. The vibration acceleration of the fastening system of ordinary railways should be ≤50m/s², and that of high-speed railways should be ≤30m/s². Excessive acceleration will lead to accelerated fatigue of components. For example, the life of spring bars will be shortened by 30%~40% under high acceleration. The resonance frequency needs to avoid the vibration frequency of the train (10~50Hz). The natural frequency of the fastening system should be ≤8Hz or ≥60Hz, otherwise resonance will occur and the amplitude will increase by 2~3 times. The fastening system in the turnout area needs to strictly control the resonance frequency. The displacement amplitude should be ≤0.3mm when the train passes, and ≤0.1mm for high-speed railways. Excessive amplitude will loosen the bolts and deform the spring bars. Ordinary railways allow a slightly larger amplitude (≤0.5mm), but they need to be re-tightened regularly. The dynamic stiffness change rate (dynamic stiffness / static stiffness) should be ≤1.3. A too large ratio indicates poor dynamic buffering performance. The fastening system of high-speed railways needs to be ≤1.2 to ensure good elasticity under dynamic loads and reduce impact transmission.
- What is the impact of train speed on the dynamic response of the fastening system?
Increasing speed will increase vibration acceleration. When the speed increases from 120km/h to 200km/h, the acceleration may increase from 30m/s² to 50m/s², which is close to the upper limit of ordinary railways. It is necessary to strengthen the dynamic performance of the fastening system, such as using high-elastic spring bars. The risk of resonance increases with the increase of speed. When the speed is 200~300km/h, the vibration frequency of the train is easy to overlap with the resonance frequency of the fastening system. It is necessary to avoid the resonance point by optimizing the structure (such as increasing damping). High-speed railways often use this method. The displacement amplitude increases with the square of the speed. The amplitude at a speed of 300km/h is 4 times that of 150km. If it is not designed properly, it will exceed the allowable value, resulting in rapid wear of components. High-strength materials and spring bars with large buckle pressure are required to resist vibration displacement. Dynamic stiffness increases at high speeds. At a speed of 300km/h, dynamic stiffness is 20%~30% higher than static stiffness, and the buffering performance decreases. It is necessary to use a low-stiffness, high-elastic pad to balance the dynamic performance. The dynamic stiffness of the high-speed rail pad is controlled at 15~25kN/mm.
- How to test the dynamic response of the fastening system?
The accelerometer used for field testing is installed on components such as spring bars and bolts. The vibration acceleration is recorded when the train passes. The sampling frequency is ≥1000Hz to ensure that high-frequency vibration is captured. The data needs to be collected continuously for more than 10 trains and the average value is taken for analysis. The laboratory uses a vibration table to simulate, apply sinusoidal or random loads (10~100Hz), measure the amplitude and acceleration at different frequencies, draw the amplitude-frequency characteristic curve, find the resonance point, and provide a basis for optimizing the design, such as determining the optimal stiffness of the spring bar. Dynamic strain testing measures dynamic stress, calculates stress amplitude and number of cycles, and evaluates fatigue life by pasting strain gauges on bolts and pressure plates. Heavy-duty railway fastening systems must be able to withstand more than 10 million cyclic loads. Long-term monitoring Install wireless sensors in key sections to transmit dynamic response data in real time, analyze changing trends, and alarm when vibration acceleration exceeds the threshold (such as high-speed rail>30m/s²) for timely maintenance. This monitoring system is usually installed in turnout areas.
- What measures can reduce the vibration response of the fastening system?
Increase the pressure of the spring clip. If the clip pressure increases by 10%, the vibration acceleration can be reduced by 15%~20%. For example, increasing the spring clip pressure from 8kN to 9kN can effectively suppress rail vibration. This method is often used in heavy-duty railways, but it needs to be matched with high-strength bolts. By using high elastic pads, the elastic modulus is reduced by 20%, and the vibration acceleration can be reduced by 25%~30%. The pads of 50~100MPa used in high-speed rails have less vibration than those of ordinary railways (80~150MPa), and the passenger comfort is significantly improved. Optimize the bolt preload, and control the preload deviation within ±5% to make the force of each component uniform and reduce the relative movement during vibration. The vibration amplitude of bolts with insufficient preload is twice the qualified one, and an intelligent wrench is required to control the accuracy. Add a damping device and install a rubber gasket between the spring bar and the pressure plate. The damping ratio can be increased from 0.05 to 0.1, the vibration energy is absorbed, and the amplitude is reduced by 10%~15%. Urban rail transit is often used because it is sensitive to noise.
- What are the differences in the dynamic response control requirements of fastening systems of different railway types?
High-speed railways have the most stringent requirements for dynamic response, with vibration acceleration ≤30m/s², resonance frequency ≤8Hz or ≥60Hz, and displacement amplitude ≤0.1mm. High-precision and high-elasticity fastening systems are required, such as Type III spring bars + low-rigidity pads, to ensure stability and comfort at high speeds. Heavy-duty railways allow slightly larger dynamic responses, with vibration acceleration ≤50m/s² and amplitude ≤0.3mm, but require high buckle pressure (≥10kN) and high-strength components to resist vibration caused by large loads and prevent loosening. Spiral spikes + high-rigidity pads are a common combination. Ordinary railways have looser control, with vibration acceleration ≤60m/s² and amplitude ≤0.5mm. An economical fastening system (Type I spring bars + ordinary pads) is used to make up for the lack of dynamic performance through regular maintenance (such as quarterly re-tightening) to balance cost and reliability. Urban rail transit needs to control vibration noise due to short station spacing and frequent starts and stops. The vibration acceleration should be ≤40m/s². Damping devices such as elastic bolts and rubber pads should be installed to reduce vibration transmission and reduce the impact on the surrounding environment.