Engineering analysis + design software

Software Option for LUSAS Bridge Plus

Rail Track Analysis

Use the LUSAS Rail Track Analysis software option to carry out  track-structure interaction analysis to the International Union of Railways Code UIC 774-3 and to the relevant sections in Eurocode 1. Automatically build models from data defined in Excel spreadsheets and quickly produce results in spreadsheet or LUSAS results file formats. Because of the nature of the analysis, the Nonlinear software option must also be accessible.

Modelling to International Union of Railways Code UIC 774-3 

UIC 773-4 Structural System

The UIC 773-3 Structural System

UIC 773-4 Track/Deck modelling

 UIC 773-3 Track/Deck Modelling


High Speed and Light Rail projects require modelling of the interaction of the track with respect to any supporting bridge structures to ensure that the effects of temperature and train loading is within specified design limits. To accurately assess these 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. Ballasted or ballast-free tracks may need to be considered.

Modelling in LUSAS

Build 3D track and bridge interaction models automatically from geometric, material property, and loading data specified within a spreadsheet. As per UIC774-3, a user-specified element length is used to define the longitudinal embankment and bridge features.

  • Define both thermal loading to the track and train loading due to acceleration and braking forces.

  • Include rail clips, ballast movement, bearings and pier stiffnesses in the analysis model, as required.

  • Consider one train crossing one or more structures, or multiple trains crossing the same structure on mixed decks / ballast. 

  • Train loads are permitted outside the extents of the model, allowing long trains to be passed over structures without having to have excessively large embankments to model the correct arrival and departure of the trainset from the structure.

A key feature of the LUSAS Rail Track Analysis software 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.

Spreadsheet input data
Full model built by LUSAS

Complete embankment and viaduct model built by LUSAS

Enlarged view of first span

Enlarged view of first span

Exploded isometric view showing embankment support and first span

Exploded isometric view of part of the model showing embankment support and the beginning of the first span


Consider deck temperature loading in isolation for subsequent analysis of multiple rail configurations, or carry out a full analysis 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

Produce results automatically in Excel spreadsheet or standard LUSAS results file format. Envelope results either inside Excel or by specifying user-defined load combinations inside LUSAS.

Viewing results in Excel

Within the Excel results spreadsheet, separate worksheets contain results for specific areas of interest. These 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.

Typical axial force results plot from LUSAS showing force in continually welded rails from temperature loading to the deck.

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 25m spans followed by three decks, each with three 25m 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. 

Compatibility with Eurocode 1

Eurocode EN 1991-2:2003 Eurocode 1: Actions on structures - Part 2: Traffic loads on bridges encompasses significant elements of the UIC 774-3 modelling approach when evaluating the combined response of the structure and track to variable actions. Limiting design criteria are the same as those specified in the UIC 774-3 code meaning that Rail Track Analysis software can be directly employed to meet Eurocode requirements.

Dependent software options

Because of the nature of the analysis involved, the use of the Rail Track Analysis option requires the following options to be accessible.

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Any modelling, design and analysis capabilities described are dependent upon the LUSAS software product, version and option in use.