Software Option for Plus
versions
Rail Track Analysis
With the growth in both High Speed
and Light Rail infrastructure projects worldwide there is a general
requirement for accurate modelling of the interaction of the track
with respect to any supporting bridge structures, and in particular,
to ensure that any interaction between the track and the bridge as a
result of temperature and train loading is within specified design
limits. When used in conjunction with the Nonlinear option, the LUSAS
Rail Track Analysis option permits track/structure interaction
analysis to the International Union of Railways Code UIC 774-3 and to
the relevant sections in Eurocode 1. It
automatically builds models from data defined in Excel spreadsheets
and quickly produces results in spreadsheet or LUSAS results file
formats.
Modelling to International Union
of Railways Code UIC 774-3
The UIC 773-3
Structural System
UIC 773-3
Track/Deck Modelling
Modelling in LUSAS
To accurately assess track-structure
interaction effects nonlinear analyses are required to investigate
thermal loading on the bridge deck, thermal loading on the rail if any
rail expansion devices are fitted, and vertical and longitudinal
braking and/or acceleration loads associated with the trainsets. This
can be done for both ballasted or ballast-free tracks.
Track and bridge interaction models are
built automatically in LUSAS from geometric, material property,
and loading data defined in a MS Excel spreadsheet. Both thermal
loading to the track and train loading due to acceleration and braking
forces can defined. Multiple trainset positions can be defined in a single MS Excel spreadsheet.
In accordance with the UIC774-3 code of practice,
a user-specified element length is used to define the longitudinal
embankment and bridge features. Rail clips, ballast movement, bearings
and pier stiffnesses are all included in the analysis model. The model
building dialogs allow for either one train crossing one or more
structures, or for multiple trains crossing the same structure.
A key feature of the LUSAS Rail Track Analysis
option is that it automatically updates the material properties associated with the
track/structure interface based upon the position of the train or
trains crossing the bridge.
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Spreadsheet
input data
Complete
embankment and viaduct model built by LUSAS
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Enlarged
view of first span |
Exploded
isometric view of part of the model showing embankment
support and the beginning of the first span |
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Analysis
When running an analysis, deck
temperature loading can be considered in isolation for subsequent
analysis of multiple rail configurations, or a full analysis can be
carried out considering the combined temperature in the deck and rail
loading. Because the response of the ballast and/or track restraining clips is nonlinear
a nonlinear analysis always needs to be carried out. For
a complete rail track assessment, dynamic effects caused by the
passage of trains that affect the structure itself should also be
considered.
Results available
Results can be produced in either Excel
spreadsheet or standard LUSAS results file format. Enveloping of
results is carried out by either choosing to do so automatically
inside Excel or by specifying user-defined load combinations inside
LUSAS.
Viewing results in
Excel
With Excel, separate worksheets within
the results spreadsheet contain results for specific areas of
interest. These worksheets include:
- Raw results data in summary, graph and tabular form for each track and deck component
- Envelopes of raw track and deck data in summary, graph and tabular form for combinations of temperature and trainset rail loading
- Tables of railbed displacements
- Tables of longitudinal reactions
- Tables of rail stress values.
The three latter tables provide key
results in summary form and allow the quick determination of which
analysis is causing the worst effects for each of the checks that need
to be carried out to the UIC774-3 code. Some example results
worksheets follow.
Envelope of axial
stresses in a rail track
Extract of Deck
worksheet showing longitudinal displacement of deck
Table of relative
displacement of Railbed (relative displacment between rails and
deck)
Viewing
results in LUSAS
Using
LUSAS a variety of similar graphs, tabular listings and results plots
can be obtained to permit checking of most key values against UIC774-3
code, but the creation and viewing of results in the Excel spreadsheet
is superior in that it
provides automatic enveloping, summaries and graphing of the key
results for each loadcase.
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Typical axial
force results plot from LUSAS showing force in continually
welded rails from
temperature loading to the deck. |
Notes
For multi-span and multi-deck structures
such as that shown above the interaction between the embankments / abutments and other decks means that the behaviour can be complex.
As an example, when considering only thermal loading on
a structure having continually welded track it is common to see a
reversal of the axial force / stress in the rails.
Whilst
not apparent from the size of the model shown, the structure illustrated above
is 325m long and consists of two decks, each with two 25 m spans followed by three decks, each with three 25 m spans. One pier / bearing support for each deck is represented by a restraining spring which takes account of the deflection characteristics of the pier / bearing system in accordance with UIC774-3. All of the remaining piers / bearing supports are roller supports allowing longitudinal movement of the decks. Under the effect of temperature on the structure the axial force / stress in either of the tracks / rails
can be seen to vary. This is primarily due
to the interaction between the movable and fixed structural
components.
Dependent software options
Because of the nature of the analysis
the use of the Rail Track Analysis option
requires the following options to be accessible.
See also:
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