علي سينا نوري

Ballasted railway tracks, due to the granular nature an‎d nonlinear behavior of ballast, are continuously subjected to settlement, deterioration of track geometry, an‎d increased impact forces caused by train passages. These conditions lead to higher vibration levels, reduced service life of track components, an‎d increased maintenance costs. Therefore, implementing solutions to improve load distribution an‎d reduce dynamic effects in railway tracks is essential. In this research, the effect of using Under Sleeper Pads (USP) on the static, mechanical, an‎d dynamic behavior of sleepers an‎d the ballasted track system was comprehensively investigated. The main objective of this study was to eva‎luate the role of USP in improving load distribution, reducing impact forces, an‎d absorbing vibrational energy. For this purpose, a series of full-scale experimental tests was conducted, including static an‎d impact loading of the track system, as well as performance tests on an individual sleeper under both USP-equipped an‎d non-equipped conditions, including flexural loading an‎d repeated dynamic loading. The results of the full-scale static loading test indicated that USP increased the vertical displacements of both rail an‎d sleeper, reduced the tracked modulus by up to 50%, an‎d resulted in a wider load distribution among sleepers. Specifically, the load contribution of the loaded sleeper decreased from approximately 53% to 44%, an‎d the load transfer zone expan‎ded from three sleepers to five sleepers. In the impact loading test, USP significantly reduced the impact force an‎d the systemʹs vibrational energy. Frequency analysis also showed that USP shifted the systemʹs dominant frequencies toward lower amplitudes an‎d reduced the overall vibration level by approximately 12 dB at the critical frequency of 63 Hz. In the flexural loading test, USP generally reduced the stiffness an‎d flexural modulus of the sleeper; reductions of up to 50% were observed under positive bending moment at the rail seat an‎d up to 80% under negative bending moment at the sleeper center, indicating increased ductility an‎d improved load distribution beneath the sleeper. Finally, repeated dynamic loading tests showed that USP increased the vertical displacement of the sleeper-track system an‎d reduced the sleeperʹs dynamic stiffness an‎d modulus by approximately two to five times. By providing controlled deformations, USP facilitated more uniform load transfer. Meanwhile, USP reduced both the peak an‎d root-mean-square (RMS) vertical accelerations of the sleeper by nearly twofold, indicating a reduction in overall vibration level an‎d dynamic energy. Overall, the results demonstrate that USP improves load distribution, reduces impact effects, an‎d decreases vibrational energy by providing controlled deformations, reducing effective stiffness, lowering impact forces, an‎d reducing sleeper acceleration. Therefore, the use of USP can be considered an effective means of enhancing long-term stability an‎d reducing maintenance costs for ballasted railway tracks.

پد زير تراورس , الگوي توزيع بار , خط ريلي بالاستي , آزمايش تجربي خط , سختي خط , سطح ارتعاش

Under Sleeper Pad , Load distribution pattern , Ballasted railway track , Experimental test , Track stiffness , Vibration level

Ali Sina Noori

Prof. Jabbar Ali Zakeri - Dr. Hamid Reza Heydari