Estimating Deterioration in the Concrete Tie-Ballast Interface Based on Vertical Tie Deflection Profile: A Numerical Study
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2016-04-12
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By Yu, Hailing
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NTL Classification:AGR-INFRASTRUCTURE-Railroads;NTL-RAIL TRANSPORTATION-Rail Safety;NTL-RAIL TRANSPORTATION-RAIL TRANSPORTATION;
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Abstract:In ballasted concrete tie track, the tie-ballast interface can
deteriorate resulting in concrete tie bottom abrasion, ballast
pulverization and/or voids in tie-ballast interfaces. Tie-ballast
voids toward tie ends can lead to unfavorable center binding
support conditions that can result in premature concrete tie
failure and possible train derailment. Direct detection of these
conditions is difficult. There is a strong interest in assessing the
concrete tie-ballast interface conditions indirectly using
measured vertical deflections.
This paper seeks to establish a link between the vertical
deflection profile of a concrete tie top surface and the tie-ballast
interface condition using the finite element analysis (FEA)
method. The concrete tie is modeled as a concrete matrix
embedded with prestressing steel strands or wires. The
configurations of two commonly used concrete ties, one with 8
prestressing strands and the other with 20 prestressing wires, are
employed in this study. All models are three-dimensional and
symmetric about the tie center. A damaged plasticity model that
can predict onset and propagation of tensile cracks is applied to
the concrete material. The steel-concrete interface is
homogenized and represented with a thin layer of cohesive
elements sandwiched between steel and concrete elements.
Strand- or wire-specific elasto-plastic bond models developed at
the Volpe Center are applied to the cohesive elements to account
for the interface bonding mechanisms. FE models are developed
for both original and worn concrete ties, with the latter assuming
hypothetical patterns of reduced cross sections resulting from
abrasive interactions with the ballast. Static analyses of
pretension release in these concrete ties are conducted, and
vertical deflection gradients along tie lengths are calculated and
shown to correspond well with the worn cross sectional patterns
for a given reinforcement type.
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