Effect of Ballast on the Dynamic Behavior of RC T-Girder Railway Bridge
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Date
2020-02-25
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Addis Ababa University
Abstract
Due to modernization of the railway transportation sector, as high speed railway lines have become more
common, nowadays researches are being been carried to assess and analyse the properties of the track
and its component besides its effect on the overall bridge dynamics.
Dynamic responses of the railway track and its elements are key parameters to measure the structural
capability of railway track and its elements. If a dynamic loading resonates the railway track’s dynamic
responses, its elements tend to possess damage from excessive dynamic stresses. for instance, a rail
vibration leads to defects in rails or wheels. The track vibrations will cause the crack harm in railway
sleepers or fasteners, or maybe the breakage of ballast support. Therefore, the identification of dynamic
properties of ballasted railway track and its elements is very essential, so as to avoid any train operation
which may trigger such resonances.
In this thesis,3D FEM models that represent the ballast as a solid part were modelled. Such systems of
modeling take sensible advantage of the capability of contemporary FEM package (Abaqus) in modeling
the continuity of the track beyond the bridge by imposing applicable boundary conditions on the railway
line. And a static load test was conducted on one tracked Prestressed T-girder railway bridge to check its
stiffness. Data from the tests was processed, and modeling the prestressed tendon like embedded element
give more realistic result compared to assuming it like cohesive element with concrete girder.
The objective of this thesis is to investigate the effect of ballast the dynamic behavior of T-girder Railway
Bridge. Hence its effect on the dynamic properties of the bridge was assessed in this thesis by
implementing and comparing different 3D FEM models of the bridge that describe different structure and
track configurations. Model that included the ballast alone showed a drop by (2.09-17.63)% in the natural
frequency for vibration mode 1-4Th and 10th and a rise by (3.07-16.52)% in the natural frequency for 5-
9th mode of vibration were observed as compared to the model that accounted for the mass of the T-girder
bridge only. In addition, different parameters influencing the natural frequencies and modes shapes of the
bridge were tested and it appears that the ballast introduces considerable additional stiffness for 5-9th
mode of vibration. Density, stiffness, depth of ballast and support condition parameters as well was found
to affect the dynamic properties of the bridge.
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Keywords
Prestressed T-girder Railway bridges, Ballast, static load test, Finite element modelling, Bridge dynamics, Modal analysis(Eigen mode analysis)