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Rail track/structure interaction analysis for the Honam high speed railway

  • Rail track / structure interaction analysis

  • Temperature, acceleration and braking loads evaluated

  • Induced rail stresses and track displacements all within design limits

Honam high speed railway - Mangyeong river crossing - artist's impression

Saman Engineering Corporation is using LUSAS Bridge analysis software for preliminary design work on the Honam high speed railway on behalf of its client the Korea Rail Network Authority. As part of this work, a rail track/structure interaction analysis has been carried out for a 1.8km long viaduct bridge structure, with a 3-span centre section of steel box framed construction, that carries the railway over the Mangyeong River near Iksan. Axial forces in the rails due to acceleration and braking forces caused by passing trains were evaluated and induced track displacements relative to the bridge deck were checked and found to be within the specified design limits.

Overview

The Honam high speed railway, when complete, will link South Korea’s capital city, Seoul, with Mokpo, a southern port city in South Jeolla Province. It will be South Korea’s second high speed railway. The first, the Seoul-Busan line, has been in operation since 2002. The Mangyeong River crossing, one of many structures on the new route, has a length of 1,875m and comprises a total of 50 spans of varying length and construction type. Three steel box framed spans of 60/75/60 metres over the river are flanked by steel girders of 50m span, and then by various numbers of 35m and 30m pre-stressed concrete box section spans for the remainder of the crossing’s length.

Rail Track Analysis

To model the bridge Saman used the LUSAS Rail Track Analysis option. This allows rail track/bridge interaction analysis to be carried out to the International Union of Railways Code UIC 774-3. It builds models automatically from data defined in MS Excel spreadsheets, runs an analysis, and produces results in spreadsheet or LUSAS formats. To do this, the bridge is simplified and ‘broken-down’ into beam elements which represent the track and any supporting structure, with nonlinear springs being used to model the ballast and expansion joints. Bearings and foundations are modelled with simple springs. Temperature change in the rails and structure, and train loadings from acceleration and braking forces must also be defined. Changes in temperature and the passage of trains on different tracks accelerating or braking across the structure induce axial compressive forces in the rails and displacements in the rails relative to the bridge deck. These needed to be evaluated to ensure that they remain below specified design values for all in-service situations.

UIC 773-4 Structural System

The UIC 773-3 Structural System

UIC 773-4 Track/Deck modelling

 UIC 773-3 Track/Deck Modelling

Typical train loading configuration

Typical train loading configuration reversed

Modelling and Analysis

For the Mangyeong River crossing, Saman created two LUSAS models to investigate the response of the structure. In one, automatically generated by the rail track analysis option, single beam elements modelled the deck and all spans of the structure. In the other, the initial rail track analysis-generated beam model was additionally edited in LUSAS to include the 3-span framed steel box members and included appropriate geometric and material properties for the added features. This somewhat unique method of increasing the accuracy of the UIC code analysis subsequently proved to be of real benefit when the results from both modelling methods were compared.

Results 

From the results obtained from the LUSAS rail track analysis Saman created graphs for both the simple model (using beams only) and the full model (which additionally modelled the framed steel members). These showed the variation of axial compressive stress in the rails as a result of the temperature and acceleration / braking loading. From these graphs it was seen that full modelling of the steel framed members produced a reduced axial compressive stress in the track over that shown for the simple beam only model - reassuring Saman in its design.

Mr Jeongil Kim, Assistant Senior Engineer in Saman Engineering's Railway Structures Department said: "Correct modelling of the nonlinear behavior of ballast, and of the interaction between the ballast and the rail track is not easy to do manually, so the LUSAS Rail Track analysis option, which handles this automatically, was very useful to us in this respect". He continues: "The easy use of the rail track analysis option was a key benefit on this project. Even though the model was built automatically we could still modify it for our own use without it ruining the original model".

Compressive stress in the rails from temperature and acceleration loading

Compressive stress in the rails from temperature and acceleration loading for
both simple (beam only) and full (including framed steel members) models
 
(click for larger image)

Compressive stress in the rails from temperature and braking loading

Compressive stress in the rails from temperature and braking loading for
both simple (beam only) and full (including framed steel members) models

 
(click for larger image)

"Correct modelling of the nonlinear behaviour of ballast, and of the interaction between the ballast and the rail track is not easy to do manually, so the LUSAS Rail Track analysis option, which handles this automatically, was very useful to us in this respect".

Mr Jeongil Kim, Engineering Manager, Saman Engineering

 

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