Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The Tubular Track (TT) railway system is a twin beam modular railway system consisting of two
reinforced concrete (RC) beams on which steel rails are continuously supported. The beams are
linked with galvanised steel gauge tie bars and continuously supported by soil foundations, and
can be used to replace conventional sleeper and ballast railway support. The TT railway system
has in the past been analysed with various analysis methods, but were found to obtain con icting
results. The con icting results means that one of the analysis methods used for the analysis and
design 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 this
investigation is therefore to develop and verify static and dynamic analysis methods and modeling
techniques which can be used to simulate the TT railway system accurately. The results and
models of the previous analyses are not explicitly investigated in this dissertation, but serve as
a motivation for this investigation.
The TT system is supported by several soil strata providing vertical support, but geometrically
modeling the subgrade strata in the analysis models adds a high level of complexity, and is not
feasible for general analysis where soil conditions are mostly unknown. The elastic foundation
theory is therefore used to accurately simulate the interaction between beam and foundation and
therefore su ciently simpli es the analysis models. Simpli cation of a subgrade foundation by
simulating 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 soil
formations currently in use at TT railway sections. The FEA of the subgrade formations indicates
that there is a linear relationship between the modulus of subgrade reaction for a square
plate bearing test and a rectangular, in nitely long plate representing the subgrade support for
the TT beams. A square plate bearing test can therefore be performed on site and modi ed to
represent the actual subgrade support sti ness of the TT railway structure, whereafter it can
be 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)
solid nite element models. The models used for the analyses are the Single and Double Beam
elastic foundation, PROKON 2D beams, ABAQUS 2D beams and ABAQUS 3D solid element
models. The alternative analysis methods considered should provide a clear indication of which
analysis 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 to
analyse the di erent analysis methods' accuracy and validity. The Double Beam, ABAQUS 2D
and ABAQUS 3D models were found to provide very similar displacements, bending moments
and shear forces for a static analysis, whereas the PROKON and Single Beam models provide
unsatisfactory results. The PROKON beam model underestimates the bending moments and
shear forces in the rail, and overestimates bending moments and shear forces in the RC beam by
a considerably margin. This result can lead to the underdesigning of the rail which could possibly
force the RC beam to be subjected to larger maximum bending moments and shear forces than
for what it was originally designed for, thereby nullifying or possibly even exceeding the amount
for which it was overdesigned. This e ectively accelerates material fatigue, which might be the
possible cause of the small cracks in the RC beams which have been found on some TT railway
sections, which is currently being investigated. A graphical user interface of the Double Beam
method is provided for quick and e cient analysis.
Empirical methods used to simulate the dynamic nature of a railway system are often used in the
industry to simplify the dynamic loading by determining a dynamic amplitude factor (DAF) to
be applied to a static load. An implicit dynamic FEA is therefore performed to obtain the DAF
for the reference section, which is subsequently used for the comparison with in-situ de ection
results. The results of dynamic analysis validates the proposed empirical analysis method, as
the displacements obtained were very similar to actual eld test results, thereby also verifying
the accuracy of the proposed analysis methods. The sensitivity of the TT system to design
parameters is also investigated to indicate to which parameters the design is sensitive to and
where small variations of these parameters require due consideration for future and analysis of
the TT railway system. / AFRIKAANSE OPSOMMING: Die Tubular Track (TT) spoorweg stelsel is 'n dubbel balk modulêre treinspoor sisteem bestaande
uit twee gewapende beton balke waarop staal spore voortdurend ondersteun word. Die balke word
gekoppel deur gegalvaniseerde staal stawe vir laterale styfheid en word deurlopend ondersteun
deur grond fondamente, en kan gebruik word om konvensionele dwarslêer en ballast spoorweg
ondersteuning te vervang. Die TT spoorweg stelsel was in die verlede met verskeie analiseringsmetodes
ontleed, maar het teenstrydige resultate gewerf. Die teenstrydige resultate beteken
dat een van die analise metodes wat gebruik word vir die analisering en ontwerp van TT spoorweg
seksies 'n onderskatting of oorskatting van verplasings, kragte, en spannings is; of beide metodes
kan selfs verkeerd wees. Die hoofklem van hierdie ondersoek is dus die ontwikkeling en veri kasie
van statiese en dinamiese analitiese metodes en modellering tegnieke wat gebruik kan word om
die TT spoorweg stelsel akkuraat te simuleer. Die resultate en modelle van die vorige ontledings
word nie uitdruklik in hierdie proefskrif ondersoek nie, maar dien as 'n motivering van hierdie
ondersoek.
Die TT stelsel word ondersteun deur verskeie grond strata wat vertikale ondersteuning verskaf,
maar meetkundige modellering van die grond strata in die ontledingsmodelle veroorsaak 'n hoë
vlak van kompleksiteit wat nie bruikbaar is vir algemene analises waar grondeienskappe meestal
onbekend is. Die elastiese fondament teorie word daarom gebruik om die interaksie tussen die
balk en die fondament akkuraat te simuleer, en vereenvoudig dus die analitiese modelle voldoende.
Vereenvoudiging van 'n grond fondament deur 'n grond styfheid ondersteuning van die TT balk
te simuleer is ondersoek en ontleed deur die resultate van eindige element analises van verskillende
grond modelle te vergelyk. Bekende ontwerp parameters van vier bekend grondformasies
wat tans gebruik word by TT spoorweg seksies word vir hierdie analises gebruik. Die eindige
element analises van die grondformasies dui daarop aan dat daar 'n lineêre verwantskap tussen
die modulus van grond reaksie vir 'n vierkantige plaat dratoets en 'n reghoekige, oneindige lang
plaat dratoets bestaan. 'n Vierkantige plaat dratoets kan dus op terrein uitgevoer en aangepas
word om die werklike styfheid van die grond ondersteuning van die TT spoorweg sisteem voor
te stel.
Die analitiese modelle wat gebruik word wissel van eenvoudige teoretiese modelle wat gebaseer is
op elastiese fondament beginsels, twee-dimensionele (2D) balk elemente, asook komplekse driedimensionele
(3D) soliede eindige element modelle. Die modelle wat gebruik is vir die ondersoek
is die Enkel en Dubbel Balk elastiese fondament, PROKON 2D balke, ABAQUS 2D balke en ABAQUS 3D soliede element modelle. Hierdie reeks bied 'n duidelike aanduiding watter analiseringsmetodes
akkuraat en haalbaar is vir die ontwerp van die TT stelsel. 'n In-situ verwysingsmodel
met bekende de eksies en ontwerp parameters wat spesi ek is vir 'n TT spoorweg
seksie word gebruik om die akkuraatheid en geldigheid van die verskillende analitiese metodes
te analiseer. Die Dubbel Balk, ABAQUS 2D en ABAQUS 3D modelle verkry baie soortgelyke
verplasings, buigmomente en skuifkragte vir 'n statiese analise, terwyl die PROKON en
Enkel Balk modelle onbevredigende resultate verkry. Die PROKON model onderskat die maksimum
buigmomente en skuifkragte in die staal spoor, en oorskat buigmomente en skuifkragte
in die gewapende beton balk. Hierdie resultaat kan moontlik lei tot die onderontwerp van die
staal spoor en dwing moontlik vir die gewapende beton balk om blootgestel te word aan groter
buigmomente en skuifkragte as vir wat dit oorspronklik ontwerp is, en verontagsaam sodoende
moontlik die kragte waarvoor dit oorontwerp is. Dit versnel e ektief materiaal vermoeiing, wat
die moontlike oorsaak is van die klein krake wat gevind is in die gewapende beton balke op
sommige TT spoorweg seksies wat tans ondersoek word. 'n Gra ese gebruikerskoppelvlak van
die Dubbel Balk model is verskaf vir vinnige en doeltre ende ontleding.
Empiriese metodes om die dinamiese aard van 'n spoorweg-stelsel te simuleer word dikwels gebruik
in die bedryf om dinamiese belasting te vereenvoudig deur middel van die gebruik van 'n
dinamiese amplitude faktor (DAF) wat op 'n statiese belasting aangewend word. 'n Implisiete
dinamiese eindige element analise word dus uitgevoer om die DAF te ondersoek, wat daarna gebruik
word vir die vergelyking met die in-situ de eksie resultate van die in-situ verwysingsmodel.
Die resultate van die dinamiese analise bevestig dat die voorgestelde empiriese analise metode
gebruik kan word, omdat die verplasings wat verkry baie soortgelyk was aan werklike veld toets
resultate, en daardeur ook die veri ëring van die akkuraatheid van die voorgestelde analise
metodes bewerkstellig. Die sensitiwiteit van die TT stelsel vir ontwerp parameters word ook
ondersoek om aan te dui watter parameters die ontwerp voor sensitief is, en waar klein variasie
in hierdie ontwerp parameters behoorlike oorweging vereis vir die toekomstige analisering en
ontwerp van die TT spoorweg stelsel.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/71741 |
| Date | 12 1900 |
| Creators | Verlinde, Karel Jef Stefaan |
| Contributors | Strasheim, J. A. v B., Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 167 p. : ill. |
| Rights | Stellenbosch University |
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