ASSESSMENT OF THE EFFECT OF HIGHER SPEED OF TRAINS ON STRENGTH REQUIREMENT OF RAILWAY TRUSS BRIDGES

Abstract

The aim of this research is to analyze strengthening requirements in the member of railway truss bridges with the variation in train speed. The first step in such a study would be an assessment of the load, which is mainly influenced by the speed of train such as vertical live load, lateral load (centrifugal load) and longitudinal load (Traction and Braking load). The next step would be to calculate the variation in the requirements of cross-sectional area in the top and bottom chords of the steel truss bridge with the variation in speed of a train. In the first phase of work, to observe the trend of variation in horizontal longitudinal forces with the variation in train speed, the equation relating train speed and coefficient of rolling friction was derived based on the information available in the existing literature. To find the distribution of longitudinal forces along the steel girder or to calculate how much longitudinal force will be transferred to the hinged end of the longitudinal girder, the solution of the governing equation given in Fryba, L. (1996) was followed. To calculate the variation in vertical live load with the variation in train speed, dynamic amplification factor for various ranges of higher train speed is calculated, which is helpful in the conversion of dynamic load into the equivalent static load. To calculate the dynamic amplification factor, following the provision of EN 1990 92, a 3D structural model in MIDAS is used. For dynamic analysis, eigenvalue analysis is performed to find the fundamental frequency of vibration, which is needed to comply with the criteria mentioned in EN 1990-92. After that, time history analysis is performed to calculate the variation of dynamic response in terms of displacement and vertical deck acceleration at different speeds of a train. Then, static analysis is performed to calculate maximum static displacement of the bridge in vertical direction. Thus, dynamic amplification factor is calculated by dividing the dynamic response with the static response of the bridge at various train speeds. In the second phase of work, a 3D truss bridge model was developed in SAP 2000 to design the bridge under the relevant loads and applicable load combinations for different speeds of a train. In this way, the cross-sectional area requirements were computed in the top and bottom chords of the truss bridge under various load combinations at different speeds of a train.