چكيده به لاتين
Today, in spite of the various developments that have happened to the ballast and double-track railway lines, there is still a need to reduce maintenance and repair operations, increase the safety of the train, and improve the level of compatibility with the environment. In recent years, the development of ladder tracks, which are also known as ladder sleepers, has been considered as a new generation of railway lines. The main structure of the ladder railway lines consists of a system with longitudinal traverses (prestressed concrete) for better support of the rails. Among the advantages of using this type of lines, we can mention increasing the stability of the line against longitudinal and transverse displacements, controlling the vibrations caused by train movement, reducing the risk of buckling of the line, more ensuring the safety of the train movement and better compatibility with the environment. . In addition, due to the structure of longitudinal traverses, the potential to reduce dynamic loads is high and there is a bed in this rail line system. Considering the wide range of advantages and privileges that can be expected in the case of using ladder lines, as well as the diversity of use and the application of this type of rail system in urban and intercity railway lines, and since in the technical literature, the effects and characteristics This type of lines has been investigated in a limited way, in this thesis, an attempt was made to numerically study the effect of support conditions on the dynamic behavior of the ladder line.
Therefore, in the present research, a numerical model of the ballast line with ladder traverses was first tried. For this purpose, a multi-layer finite element model including rail layers, traverse, upper ballast, lower ballast and rail bed and ladder traverses was built. In this regard, the Euler-Bernoulli beam element was used to model the ladder rail and traverse, the spring-damper element was used to simulate the pad under the rail, and the set of mass-spring-damper elements was used to construct the top (upper and lower) and bed layers. Then the results of the model were validated and validated by comparing with the results of a laboratory study. In the following, two types of evaluations were carried out on the ballast ladder line from the point of view of the influence of the support conditions on the dynamic behavior of the line and its components, as well as the vibration behavior of the line:
a) First, by analyzing the sensitivity on the geometric dimensions of the ladder traverse (including length, width, thickness), while determining the effects of these characteristics on the behavior of the rail line and its components, it was tried to identify the optimal dimensions of the ladder traverse which has a better performance from a dynamic and vibration point of view. be introduced The results of these studies show that the ladder traverse with a length of 6-9 meters, a width of 0.6-0.7 meters, and a thickness of 0.25-0.3 meters has a better performance in terms of dynamic and vibrational effects.
b) Then the ladder line with different support conditions was analyzed and evaluated from the point of view of hardness and flexibility. In this regard, there are four types of ladder lines with different support conditions, including normal ladder line (with a pad under the single rail), floating ladder line (FLT/continuous pad under the rail), traverse ladder with elastic pads (USP / pad under the traverse) and ladder line with Ballast carpet (UBM/under-ballast pad) were analyzed and investigated. The results of this investigation show that the maximum acceleration values of rail vibrations in floating ladder lines, with a pad under the traverse and with ballast carpet, have been reduced by 55%, 37.5% and 20%, respectively, compared to the normal ladder line. In addition, the results of the traverse frequency analysis show that the floating ladder line, the ladder line with a pad under the traverse and the ladder line with the ballast carpet have performed best in the range of frequencies from 30 to 80 and on average 12.3, 3.1 and 1.2 dB respectively. They have caused the reduction of vibrations compared to the ladder line.
