The phenomenon of unsupported Sleepers is considered one of the most critical factors affecting the dynamic performance of ballasted railway tracks. Disrupting the contact between the Sleeper and the ballast leads to increased deflection, stress concentration, and reduced track stability. This study aims to numerically analyze and simulate the dynamic effects of unsupported Sleepers, focusing on their numbers and layout patterns in the ballasted railway tracks. For this purpose, a three-layer mechanical model consisting of rail, Sleeper, and ballast was developed in MATLAB, and its results were compared with an equivalent finite element model created in ABAQUS. The MATLAB model employs mass, stiffness, and damping matrices along with a time-dependent moving load to evaluate the system's response under various unsupported Sleeper conditions. In the ABAQUS model, Sleepers and ballast were modeled as concentrated masses, with their interactions represented via equivalent spring-damper systems; loading was applied incrementally along the train path. The results indicate that increasing the number of unsupported Sleepers—particularly in sequential arrangements—significantly amplifies rail deflection and mid-span stress, with the most critical response observed in the case of three-consecutive-unsupported-Sleepers. These findings indicate the necessity of continuous monitoring and preventive maintenance of unsupported zones to ensure track safety and extend structural service life.

One of the main problems of the damages of rail tracks which is caused by track settlement is unsupported Sleeper. Due to this defect the underlying area of Sleeper is not supported on the ballast and causes the Sleeper displacement to increase. The increase creates vibration in the track and vehicle components and causes problems on their performance. Hence, in this study the investigation of rail displacement in tracks with unsupported Sleeper has been dealt with. Three dimensional modeling of the vehicle and ballasted track has been carried out using ANSYS and SIMPACK programs. To use this software, the modeling of a flexible track in the vehicle multibody model is possible. Ballasted track which is formed from components as rail, Sleeper and ballast, has been considered to be flexible. In simulating the vehicle all of its main components have been considered and damping and stiffness values of bogie suspension systems have been considered to be nonlinear. The results obtained from numerical simulation have good agreement with field test results. The results show that the speed of the vehicle on the track displacement with less than four unsupported Sleepers has no effect, but by increasing the number of unsupported Sleepers, the effect of increasing velocity would be considerable.

Identifying the contribution of each part of the railway to total lateral resistance is considered the most important issue in choosing type of Sleeper for providing lateral stability of ballasted railway track. On the other hand, identifying the percentage of effect of each part can help to present new methods for increasing lateral resistance of ballasted railway track. Methodology of this study was based on experimental work in the laboratory. In this paper, the contribution of each part of the Sleeper comprised of base, crib and shoulder was determined in the total lateral resistance by STPT tests. In all of the measurements, the greatest value of lateral resistance was related to the area under the Sleeper (base zone) and its corresponding valuesin concrete, steel and wood Sleepers were 62%, 56% and 51%, respectively. The contributions of shoulder and crib area to the lateral resistance were28% and 9% for concrete Sleeper, 27% and 22% for wooden Sleeper and 18% and 26% for steel Sleeper, respectively.

In this paper, stress analyses in concrete Sleeper has investigated by using results of the tests which have been done in main line of railway track. In these tests, special concrete Sleeper (B70) installed in railway track. Five load cells fixed inside of the Sleeper during constructing of that. After replacing this special Sleeper with ordinary Sleeper, and tamping in railway track, a train with certain axle load passed through that point of track. Forces on Sleeper are analyzed (output of measurement). The results show that B70 concrete Sleepers are designed well for tamped and no tamped cases. In the both cases, the stresses in Sleeper cross sections are in allowed range. Also, the results show that the track without DTS operation (after replacing of the Sleeper) decreases share of Sleeper bearing and increases forces on adjacent Sleepers. These forces together with dynamic effect of rail-Sleeper interaction will accelerate Sleeper's deterioration. This means that after replacing failured Sleepers, the sufficient length of track must be operated by DTS and Tamping machines.

In recent years, ladder tracks, which are also described as tracks with ladder Sleepers, have been developed as a new generation of railway tracks. The structure of the ladder tracks especially includes a combined Sleeper consisting of longitudinal and lateral beam elements, which are considered the main support of the rails. Some of the main advantages of using this type of railway track are increasing the stability of the track against longitudinal and lateral forces, reducing dynamic and vibration effects, reducing the risk of buckling, increasing safe train movement, reducing maintenance costs, etc. In this study, the influence of ladder Sleeper length on the dynamic behavior of railway tracks was investigated through numerical modeling. For this purpose, a four-layer model including rails and ladder Sleepers was simulated based on the finite element method. According to the results obtained from the sensitivity analyses, the maximum acceleration of the Sleeper with 6-9 m units is reduced by about 22-40%, compared to the common railway track with B70 concrete Sleepers. Also, the maximum displacements of the ladder Sleeper with 6-9 m length show a reduction of about 27% compared to the track with the B70 Sleeper. Therefore, it can be concluded that the ladder unit with a 6-9 m length shows more dynamic performance generally.