Finite element analysis of tubular track system

[摘要] ENGLISH ABSTRACT: The Tubular Track (TT) railway system is a twin beam modular railway system consisting of tworeinforced concrete (RC) beams on which steel rails are continuously supported. The beams arelinked with galvanised steel gauge tie bars and continuously supported by soil foundations, andcan be used to replace conventional sleeper and ballast railway support. The TT railway systemhas in the past been analysed with various analysis methods, but were found to obtain con ictingresults. The con icting results means that one of the analysis methods used for the analysis anddesign of TT railway sections is either an underestimation or overestimation of section displacements,forces, and stresses; or both methods could even be incorrect. The main emphasis of thisinvestigation is therefore to develop and verify static and dynamic analysis methods and modelingtechniques which can be used to simulate the TT railway system accurately. The results andmodels of the previous analyses are not explicitly investigated in this dissertation, but serve asa motivation for this investigation.The TT system is supported by several soil strata providing vertical support, but geometricallymodeling the subgrade strata in the analysis models adds a high level of complexity, and is notfeasible for general analysis where soil conditions are mostly unknown. The elastic foundationtheory is therefore used to accurately simulate the interaction between beam and foundation andtherefore su ciently simpli es the analysis models. Simpli cation of a subgrade foundation bysimulating a soil sti ness supporting the TT beam is investigated and analysed by comparing nite element analysis (FEA) results of various soil models using parameters of four known soilformations currently in use at TT railway sections. The FEA of the subgrade formations indicatesthat there is a linear relationship between the modulus of subgrade reaction for a squareplate bearing test and a rectangular, in nitely long plate representing the subgrade support forthe TT beams. A square plate bearing test can therefore be performed on site and modi ed torepresent the actual subgrade support sti ness of the TT railway structure, whereafter it canbe used for the analysis and design of the TT system using one of the proposed analysis methods.The analysis models used range from simple theoretical models based on elastic foundation principles,to two-dimensional (2D) beam elements, and ultimately to complex three-dimensional (3D)solidnite element models. The models used for the analyses are the Single and Double Beamelastic foundation, PROKON 2D beams, ABAQUS 2D beams and ABAQUS 3D solid elementmodels. The alternative analysis methods considered should provide a clear indication of whichanalysis methods are accurate and feasible for design of the TT system. An in-situ reference model with known de ections and design parameters speci c to a TT railway section is used toanalyse the di erent analysis methods' accuracy and validity. The Double Beam, ABAQUS 2Dand ABAQUS 3D models were found to provide very similar displacements, bending momentsand shear forces for a static analysis, whereas the PROKON and Single Beam models provideunsatisfactory results. The PROKON beam model underestimates the bending moments andshear forces in the rail, and overestimates bending moments and shear forces in the RC beam bya considerably margin. This result can lead to the underdesigning of the rail which could possiblyforce the RC beam to be subjected to larger maximum bending moments and shear forces thanfor what it was originally designed for, thereby nullifying or possibly even exceeding the amountfor which it was overdesigned. This e ectively accelerates material fatigue, which might be thepossible cause of the small cracks in the RC beams which have been found on some TT railwaysections, which is currently being investigated. A graphical user interface of the Double Beammethod is provided for quick and e cient analysis.Empirical methods used to simulate the dynamic nature of a railway system are often used in theindustry to simplify the dynamic loading by determining a dynamic amplitude factor (DAF) tobe applied to a static load. An implicit dynamic FEA is therefore performed to obtain the DAFfor the reference section, which is subsequently used for the comparison with in-situ de ectionresults. The results of dynamic analysis validates the proposed empirical analysis method, asthe displacements obtained were very similar to actualeld test results, thereby also verifyingthe accuracy of the proposed analysis methods. The sensitivity of the TT system to designparameters is also investigated to indicate to which parameters the design is sensitive to andwhere small variations of these parameters require due consideration for future and analysis ofthe TT railway system.

[发布机构] Stellenbosch University