Analysis of the transition between Tubular Modular Track and ballasted railway

Visser, Deon (2016-03)

Thesis (MEng)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: Tubular Modular Track (TMT) is a relatively new rail design invented in 1989. The system is ballastless and is designed to continuously support the rails on twin reinforced concrete (RC) beams which are founded on a specially designed subgrade. These RC beams are linked together by galvanised steel gauge bars which encircle the RC beams and provide links to fasten the rails to the RC beams with the use of rail clip fasteners. Elastomeric pads are placed in-between the rail and the RC beam to provide shock and sound absorption and grout is placed below the RC beams to level the TMT beams and ensure constant contact between the RC beams and the subgrade. With the introduction of high speed trains and ballastless rail systems the design of the transitions between ballasted and ballastless rails needs special attention. Multiple studies have been done on transitions between various types of ballastless rail and ballasted rail, but limited research is available on transitions between TMT and ballasted rail. To improve the confidence in the use of the TMT system in a transition various analyses are performed on the RC beam, the main supporting component of the system, for varying train speeds and varying rail irregularity angles due to elevation changes in the rail which occur because of ballast settlement at the track transition. The TMT structure is supported by different layers of subgrade which need to be incorporated in the finite element (FE) model of the system, but modelling the subgrade as a continuum increases the computational cost of the analysis. To simplify the modelling of the subgrade elastic foundation theory with plate bearing test (PBT) models are investigated. The subgrade can then be replaced with an elastic support. The PBT model and the elastic subgrade stiffness are verified by using previous research models which simulate PBT and determine an elastic stiffness to replace the subgrade. To analyse the TMT structural components a static, three-dimensional (3D), FE model is created of the structure. The TMT 3D model is also verified using models used in previous research which analysed the TMT structure. A 3D model of the structure requires a fine mesh to accurately model the cross sections of the TMT components, making the analysis computationally expensive. To simplify the model a two-dimensional (2D) model is created using beam and plane stress elements. For the 2D model a damping factor sensitivity analysis is performed to determine the influence of damping on the behaviour of the structure. The 2D model is then loaded statically and dynamically to determine the dynamic amplification factor (DAF) for the displacements, bending moments and shear forces in the rail and RC beam. In order to create the ballast to the TMT transition model, a model of the ballasted rail is required. A 3D discrete element (DE) model of the ballasted rail was attempted by modelling the ballast as discrete particles in the 3D space and placing the rail and sleepers on the particles. The discrete element method (DEM) was found to be a complex method of modelling the ballast and required time expensive analyses. Convergence errors were encountered in the modelling and analysis process. Due to limited available assistance and knowledge the results of the DEM model were inconclusive. This problem can be attributed to the fact that DEM is a new feature introduced into the available software, i.e. Abaqus. A similar approach to the simpli cation, analysis and results presentation of the TMT 2D model was used for the ballasted model. Plane stress, plane strain and 2D beam elements are used and the ballast and subgrade are modelled according to the elastic foundation theory in order to simplify the ballasted rail model. To calibrate the model results displacement measurements, taken on a reference ballasted rail, are compared to the model displacement results. The model is loaded statically and dynamically to determine the DAF for the displacements of the rail and sleepers and the bending moments and shear forces of the rail are presented. The ballast to TMT transition model is created by combining the simpli ed ballast and TMT 2D models. To calibrate the modelling of a transition with simpli ed 2D methods site displacement measurements are compared to the displacement results of a calibration model. After calibration various dynamic models are created of the ballast to TMT transition to investigate the impact of the transition on the displacements, bending moments and shear forces in the TMT RC beam. Sixteen ballast to TMT transition models with varying train speeds and irregularity angles are created and the results of these models were used in a sensitivity analysis for the response of the RC beam. Results show that RC beam displacements, maximum hogging bending moments and shear forces are sensitive to an increase in train speeds, but are more sensitive to an increase in rail irregularity angle. The maximum sagging bending moments remain constant because wheel loads remain the same for all models. It is concluded that the design of a transition zone should focus on achieving gradual elevation change between supporting structures rather than increasing the stiffness of the ballasted structure at the transition. Regular track maintenance to limit elevation changes at the transitions due to subsidence of the ballasted rail is also of utmost importance to limit the bending moments and resulting stresses in the rail components.

AFRIKAANSE OPSOMMING: Tubular Modular Track (TMT) is 'n relatiewe nuwe spoorondersteuningstelsel wat in 1989 ontwerp is. Die sisteem maak nie gebruik van ballas nie, maar is ontwerp om die spoorstawe deur middel van twee gewapende beton balke, wat op 'n spesiale grondformasie neergelê is, te ondersteun. Gegalvaniseerde staal stawe bied vasmaakplek vir die spoorstawe en word gebruik om die beton balke aan mekaar te koppel deurdat dit die balke omring. Elastomeriese kussings tussen-in die spoorstawe en beton balke verskaf skok- en klankdemping aan die sisteem en voegbry word onder die beton balke geplaas om die korrekte hoogte te verseker en om konstante kontak tussen die beton balke en fondament te verseker. Met die gebruik van hoëspoedtreine en nuwe spoorsisteme (wat nie van ballas gebruik maak nie) word spesiale aandag aan die ontwerp van oorgange tussen spore met ballas en spore sonder ballas geverg. Verskeie studies is al oor die oorgange tussen verskillende spoorsisteme gedoen, maar beperkte navorsing oor die oorgang tussen ballas-spore en TMT is beskikbaar. Om die vertroue in die gebruik van die TMT spoorsisteem in spooroorgange te verbeter is verskeie analises van die gewapende beton balke, die hoof ondersteuningskomponente van die TMT sisteem, in hierdie ondersoek uitgevoer. Die analises is met wisselende treinsnelhede en wisselende hoeke van onreëlmatigheid in die spoor, wat as gevolg van die versakking van die ballas by die spooroorgang plaasvind, uitgevoer. Die TMT struktuur word deur verskeie formasielae wat in die eindige element (EE) model in aanmerking gebring moet word ondersteun, maar deur die formasie as 'n kontinuum te modelleer word die analise se berekeningskoste verhoog. Om die formasiemodellering te vereenvoudig word die elastiese fondasieteorie en die plaatdraagtoets (PDT) ondersoek. Dan kan die formasie met 'n elastiese ondersteuning vervang word. Die PDT en die elastiese formasiestyfheid is deur vorige navorsing, wat die PDT simuleer en die elastiese formasiestyfheid bepaal, veriëer. 'n Statiese, drie-dimensionele (3D) EE model is van die TMT struktuur geskep om die komponente van die struktuur te analiseer. Die TMT 3D model is ook deur vorige navorsing, wat die TMT struktuur analiseer het, geveriëer. Vir 'n 3D model van die struktuur word 'n fyn maas benodig om die dwarssnit van die verskeie TMT komponente akkuraat te modelleer. In terme van berekeningstyd maak dit die analise van die struktuur duur. Om die model te vereenvoudig word balk- en vlakspanningselemente gebruik om 'n twee-dimensionele (2D) model van die struktuur te skep. Die invloed van demping op die gedrag van die struktuur word bepaal deur 'n sensitiwiteitsanalise vir demping uit te voer. Daarna is die struktuur staties en dinamies belas om die dinamiese vergrotingsfaktor (DVF) vir die verplasings, buigmomente en skuifkragte in die gewapende beton balke te bepaal. iv Om die model van die oorgang tussen ballas-spoor en TMT te skep word 'n model van die ballas-spoor benodig. 'n Poging was aangewend om 'n 3D diskrete element (DE) model van die ballas spoor te skep deur die ballas as diskrete partikels in die 3D ruimte te modelleer en die spoorstawe en dwarslêers bo-op die partikels te plaas. Daar is gevind dat die diskrete element metode (DEM) 'n komplekse metode is om die ballas te modelleer en dat dit tydsgewys duur is om te analiseer. Konvergeringsfoute vir die modellering en analiseproses van die DEM model was teëgekom. Die resultate van die DEM model was, as gevolg van beperkte kennis en beperkte toegang tot bystand, onbeslis. Die probleem kan toegeskryf word daaraan dat DEM 'n nuwe toevoeging tot die beskikbare sagteware (Abaqus) is. Vir die vereenvoudiging, analise en die aanbieding van resultate van die ballasmodel was 'n soortgelyke benadering as die vir die TMT model gebruik. Om die model te vereenvoudig is 2D balk-, vlakspannings- en vlakvervormingselemente gebruik en die ballas en formasielae is volgens die elastiese fondasieteorie gemodelleer. Verplasingsmetings, gemeet op 'n verwysings ballas-spoor, is met die model se verplasingsresultate vergelyk om die model te kalibreer. Daarna is die struktuur staties en dinamies belas om die DVF vir die verplasings van die spoorstaaf en dwarslêers en die buigmomente en skuifkragte van die spoorstaaf te bepaal. Die model van die oorgang tussen die ballas-spoor en TMT is geskep deur die onderskeie, vereenvoudigde 2D modelle met mekaar te kombineer. Om die modellering van die oorgang met vereenvoudigde 2D modelle te kalibreer is verplasingsmetings van 'n bestaande spoor met die verplasingsresultate van 'n kalibrasie oorgangsmodel vergelyk. Na kalibrasie is daar verskeie dinamiese modelle van die oorgang tussen die ballas-spoor en TMT geskep om die impak van die oorgang op die verplasings, buigmomente en skuifkragte in die TMT gewapende beton balke te bepaal. Sestien oorgangsmodelle met wisselende treinsnelhede en onre elmatigheidshoeke is geskep en die resultate van hierdie modelle is in 'n sensitiwiteitsanalise vir die reaksie van die beton balke gebruik. Die resultate wys dat die verplasings, sakkingsbuigmomente en skuifkragte in die beton balke sensitief vir 'n verhoging in treinsnelheid is, maar nog meer sensitief vir 'n verhoging in die onreëlmatigheidshoek is. Die opbuigingsmomente bly konstant, omdat die wiellaste vir al die modelle konstant bly. Die gevolgtrekking word gemaak dat 'n oorgansone 'n geleidelike oorgang in die ligging van die spoor tussen verskillende spoorsisteme moet bied, in plaas daarvan om die styfheid van die ballas-spoor by die oorgang te verhoog. Gereelde spooronderhoud is ook uiters belangrik om die veranderinge in spoorligging, as gevolg van versakking in die ballas-spoor by die spooroorgang, te beperk, om die buigmomente en gevolglike spannings in die spoorkomponente te beperk.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98681
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