Developing a Method for Functional and Vibration Analysis of Light Mass-Spring Systems

Mass-Spring systems are widely used as the most effective LRT systems in urban areas. When considering this system in railway superstructure, vibration-prone regions and dense residential areas are among the most feasible and efficient design options. Similar to vehicle suspension system, a part of the mass of the track structure can be dynamically sprung, in railway superstructure mass-spring systems.In this system, a spring element is needed which is often chosen from rubber or poly-urethane materials. The characteristics of the sprung mass in terms of weight, live loads, rigidity and etc. are influential in vibration damping and elastic properties of the system. The elastic element in these systems contributes more than just a spring element. Since many of mass-spring systems are adapted in slab tracks (ballast-less tracks), they can also be used to increase the elasticity of the track system which in turn results in lower dynamic loads, better deflection behavior and lower maintenance costs. In this regard, in MSS systems, the improvement of the system elasticity as well as vibration damping behavior should be considered. The fields of application of Mass-Spring system can be extended in Iranian railway network and urban railways.Dense urban and rural residential areas, ancient areas, auditoriums, concert halls, studios, labs and buildings containing precise measurement devices are sensitive to railway vibration and should be protected against transmitting ground motions resulting from passing trains. Iranian major cities are experiencing a heavy urban railway construction. In some ancient cities like Isfahan, the national heredities should be protected from the oncoming vibrations resulting form moving LRVs after operation. In this regard the need of an efficient vibration damping system has been realized, among which the mass-spring systems are noticeable. In this paper, a simple as well as accurate analysis method for these systems is developed. The results of vibration and elastic analysis of the mass-spring system used in Isfahan are presented and are compared with the international criteria and standards. The Scandinavian vibration criteria adapted from Swedish Transport Research Center are used to preliminary evaluate the vibration impacts of the LRT line on the vibration-prone buildings and ancient construction. In this paper vibration damping criteria of -20ΔdBv is suggested for ancient cities.This criterion should be fulfilled in LRT tracks in working frequency domain above 50 Hz. The use of Poly-Urethane elastic layers and minimum weight of the sprung mass of 6 ton/m are also recommended in this paper. The natural frequency of LRT MSS system should be as low as 18 Hertz to be efficient. In the mean time, a soft track system (in terms of track modulus) should be avoided. On this basis in this paper the vibration analysis of the system is accompanied by track deflection analysis. For operation reasons, the maximum dynamic and static track deflection are limited to 3 and 4 cm. respectively.