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An investigation of overhead crane wheel/rail/girder interactionPerez Winkler, A. R. 03 1900 (has links)
Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The aim of this thesis is to investigate the wheel/rail/girder interaction of overhead cranes. Three
components of the above mentioned interaction system are considered.
• The contact interaction between the crane wheel and the rail and its effects on the rail
stresses.
• The stress distribution in thin webbed rails and the location of critical stresses in the rail.
• The load distribution between the rail foot and the crane girder with the inclusion of
elastomeric pads.
The steps followed for the purpose of this investigation were:
• The creation of a numerical wheel-rail interaction model with the finite element method.
• The experimental and analytical verification of the numerical results.
• An analysis of the wheel/rail/girder interaction system variables on the basis of the
numerical results.
The following conclusions were drawn from the investigation:
• The variables with the greatest influence on the wheel-rail contact patch shape, size and
critical stress are the crane wheel diameter and the railhead curvature radius.
• It is the position of the above mentioned contact patch relative to the rail symmetry plane,
rather than the wheel-rail contact patch size, shape and critical stress, that has a significant
influence on the rail stress distribution as a whole.
• Critical stresses in thin webbed rails are found at the web-foot and web-head junctions.
• The load distribution between the rail foot and the girder, in case elastomeric pads are
included, can be described using the beam on elastic foundation theory. / AFRIKAANSE OPSOMMING: Die doél van hierdie tesis is om die interaksie tussen die wiel, die spoor en die ondersteunende
balk van oorhoofse krane te ondersoek. Die klem val op die interaksie van drie komponente van
bogenoemde sisteem nl:.
• Die kontak: interaksie tussen die kraanwiel en die spoor en die gevolglik effekte op die
spanningsverdeling in die spoor.
• Die spanningsverdeling in kraanspore met dunwandige webbe en die lokasie van kritieke
spannings.
• Die spanningsverdeling tussen die onderste spoorflens en die bo-flens van die
ondersteunende balk in die geval dat 'n elastomeriese strook tussen bogenoemde flense
ingesluit word.
Die stappe vir die ondersoek was as volg:
• Die skepping van 'n numeriese wiel-spoor interaksie model met die eindige element
metode.
• Die eksperimentele en analitiese verifikasie van numeriese resultate.
• Die analise van die wiel/spoor/ondersteunende balk sisteem veranderlikes gebaseer op
numeriese resultate.
Die belangrikste resultate van die ondersoek was dat:
• Die veranderlikes met die grootste invloed op die grote, vorm en kritieke spannings van
die wiel-spoor kontak area is die kraan wiel radius en die radius van die spoor se bo-vlak
kromming. Dit is die posisie van bogenoemde kontak area relatieftot die simmetrievlak
van die spoor, in plaas van die wiel-spoor kontak area grote, vorm ofkritieke spanning,
wat 'n deurslaggewende invloed op die spanningsverdeling in die kraanspoor het.
• Kritieke spannings in spore met dunwandige webbe word aan die bokant en onderkant
van die spoor web aangetref.
• Die spanningsverdeling tussen die onderste spoor flens en die bo flens van die
ondersteunende balk kan, in die geval dat 'n elastomeriese strook tussen bogenoemde
flense ingesluit word, met die gebruik van balk op elastiese fondament teorie beskryf
word.
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The development of a multi-purpose beam/column testing apparatusKoen, Colin Boyd 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: A multi-purpose beam/column apparatus is developed to ensure successful testing of
structural elements and to optimise the main test floor of the Structures Laboratory of the
University of Stellenbosch. An overview of the testing of structural elements is given as
background to beam and column testing, with specific reference to the test sample, the test
arrangement and the test data. The test arrangement, with reference to the test setup
boundary conditions (static and kinematic), and the loading are discussed. A summary of
the collection and the processing of the test data is given and frequently used and standard
test setup is described.
The requirements and the various components of the testing apparatus are discussed and a
three-dimensional CAD model of the apparatus is developed to illustrate the versatility of
the apparatus.
A rational planning process is developed to optimise the testing and pre-test planning
process with specific reference to the use of the apparatus. This rational planning process is
defined as the process of preparing, testing and evaluating structural tests and together with
the literature review will ensure meaningful test results.
The use of the apparatus, built by the Department of Civil Engineering, University of
Stellenbosch and the use of the rational planning process are illustrated by testing the
deflection of a welded truss, from which conclusions are drawn. / AFRIKAANSE OPSOMMING: 'n Veelsydige balkkolom apparaat is ontwikkel om die gebruik van die hoof-toetsvloer van
die Struktuur Laboratorium van die Universiteit van Stellenbosch te optimiseer en
suksesvolle struktuurtoetse te verseker. As agtergrond tot die ontwikkeling van die MTA
word 'n oorsig gegee oor balk-en-kolom toetse, met spesifieke verwysings tot die toetsstuk,
die toets-opstelling en die toets-data. Die toets-opstelling word bespreek met
spesifieke verwysing na die grenstoestande (staties en kinematies) en die aangewende
belasting. Die versameling en die verwerking van toetsdata en die algemeen gebruikte en
standaard toets-opstellings word bespreek.
Die vereistes van die verskillende komponente van die apparaat word bespreek en 'n driedimensionele
CAD model van die apparaat word gebruik om die veelsydigheid van die
apparaat te beklemtoon. 'n Rasionele beplanningsproses, wat spesifiek verwys na die
gebruik van die apparaat, word ontwikkel. Hierdie beplanningsproses wat die beplanning,
uitvoer en evaluasie van strukturele toetse insluit, saam met die literatuur agtergrond,
verseker sinvolle toetsresultate.
'n Gesweisde vakwerk word getoets om die gebruik van die apparaat, gebou deur die
Departement van Siviele Ingenieurswese, Universiteit van Stellenbosch en die gebruik van
die rasionele beplanningsproses te illustreer. Gevolgtrekkings word gemaak na aanleiding
van hierdie toetse.
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Investigation into the top flange and web deformation in a crane girder panelViljoen, P. de K. 12 1900 (has links)
Thesis (MEng) -- Stellenbosch University, 2004. / ENGLISH ABSTRACT: The purpose of this project was to study the deformations of the top flange and web of
a girder panel resulting from loads, which have been imposed by an overhead
travelling crane. This was achieved by designing a crane girder that represents
dimensional ratios occurring in practice.
The first part of this project attempts to determine the properties of the crane girder.
The crane girder was built from drawings in the workshop of the University of
Stellenbosch’s Civil-Department. Positions were identified where the strains were to
be measured on the crane girder. The crane girder was subjected to loads according to
SABS 0160 - 1989 and measurements were taken. The same beam was also modelled
with finite elements. The numerical model was subjected to the same loads as the
experimental crane girder.
Comparisons were then made between the results of the experimental investigation
and those of the numerical model. Good comparisons were achieved between the
results and the numerical model was assumed to be correct.
Other students could now use this model for investigating local stresses and strain
effects that might cause fatigue and other in-service problems of electric overhead
travelling cranes support structures in practice. / AFRIKAANSE OPSOMMING: Die doel van hierdie projek was om die vervormings van die boonste flense en web
van ’n kraanbalkpaneel te ondersoek, as gevolg van laste wat onderworpe was aan ’n
oorhoofse kraanbalk. Dit was bereik deur ‘n balk te ontwerp wat dimensionele
verhoudings in die praktyk verteenwoordig.
In die eerste gedeelte van die projek word die eienskappe van die kraanbalk bepaal.
Die kraanbalk was vanaf tekeninge in die werkswinkel van die Universiteit van
Stellenbosch se Siviele Departement gebou. Posisies was geidentifiseer waar die
vervormings op die kraanbalk gemeet sou word. Die kraanbalk was onderwerp aan
laste volgens SABS 0160 - 1989 en meetings was geneem. Dieselfde balk was ook
gemodelleer met eindige elemente. Die numeriese model was aan dieselfde laste as
die eksperimentele balk onderwerp.
Vergelykings was toe verkry tussen the resultate van die eksperimentele ondersoek en
die numeriese model. Goeie vergelykings tussen die resultate was behaal en die
numeriese model word as korrek aanvaar.
Ander studente kan nou hierdie model gebruik vir die ondersoek na lokale spannings
en vervormingseffekte wat moontlik vermoeidheid en ander in-diens probleme van
elastiese oorhoofse kraan ondersteunende strukture in the praktyk kan veroorsaak.
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Object-oriented finite element frameworkOlivier, Albertus Hendrik 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: The role of the computer has changed from a calculation tool to a tool that supports human
thinking.
In this thesis fundamental aspects of the Finite Element method are mapped to an object
model with a well defined structure which provides for local and distributed analysis work.
To achieve this the following was investigated:
• An object-oriented framework for the Finite Element analysis method
• An associated graphical user interface that enables the user to create and modify
Finite Element models in an effective way
• Requirements for the sharing of analysis information in a communication network
Proposed solutions are implemented in a pilot application which indicates their potential. / AFRIKAANSE OPSOMMING: Die rol van die rekenaar het verander vanaf 'n gereedskapstuk wat berekening doen na 'n
gereedskapstuk wat menslike denke ondersteun.
In hierdie tesis word die fundamentele aspekte van die Eindige Element metode oorgedra na
'n objek model met 'n goed gedefinieerde struktuur wat lokale en verspreide analisering werk
ondersteun.
Om dit te bereik is die volgende ondesoek:
• 'n Objek orienteerde raamwerk vir die Eindige Element metode
• 'n Geassosieerde grafiese raamwerk wat die gebruiker in staat stelom objekte te
skep en te verander
• Vereistes vir die deel van analise inligting in 'n kommunikasie netwerk
Die voorgestelde oplossing is geimplimenteer in 'n loodsimplementering wat die voordele van
die benadering uitlig.
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Factors influencing asphalt compactibility and its relation to asphalt rutting performanceDouries, William John 04 1900 (has links)
Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This thesis covers the factors affecting compactibility of hot mix asphalt including gradation,
filler/binder ratios, binder types, binder content, polymer modification, temperature, volumetric
properties etc. The study is not limited to compactibility as the property measured, but also on
the influence of these factors on the mix’s capacity to resist permanent deformation or rutting.
An experimental design was used with a variety of the above factors being included.
Laboratory analysis of the mixes as well as accelerated pavement testing of different mix types
using the one-third scale Model Mobile Load Simulator (MMLS3) was carried out. The
analysis assists in identification of the factors that influence both compactibility and rut
resistance, those influencing the one but not the other, and those factors having no significant
influence. The compactibility of the mixes has been analysed in terms of voids in the mix at a
specific binder content and compaction level. Special consideration was given to the
characterisation of the filler and filler/binder system of some mixes.
It was found that gradation of a mix has a significant influence on compaction and the rutting
performance. High filler/binder ratios were found to be the critical factors influencing the
compactibility of the wearing course mixes investigated, but based on the limited tests
performed, the reduction of the filler/binder ratios for improved compactibility did not
significantly increase rutting under accelerated pavement testing.
As expected, the binder type has a significant influence on the rutting resistance as well as
compactibility. In addition, an increase in binder content facilitated compaction, but decreased
rutting resistance.
Polymer modification considerably improved the rutting resistance of a standard mix under the
same loading conditions. Although some modifiers may improve rutting resistance, it requires
higher compaction temperatures.
The addition of the antistripping agent Gripper L decreased the rutting, aggregate stripping and
also the rate of rutting of the Quartzite LAMBS mix that result from the stripping failuremechanism. Low densities can lead to considerable rutting and moisture damage, especially
when a moisture susceptible aggregate is used.
In terms of compactibility as evaluated with the Superpave Gyratory Compactor, it appears that
there exists a temperature window in which compaction can be achieved, but in terms of
rutting; even a small deviation in temperature can influence rutting results significantly. The
control of the temperature during testing is critical if meaningful comparisons between
different mixes with regard to rutting performance are to be made.
Linear elastic and finite element analysis has been performed to ascertain whether different
specimen geometries would influence the stress distribution within the specimen, and
subsequently the rutting results. It was found that the geometry of test specimens has an
influence on the stress distribution within the specimens, which can influence the permanent
deformation results. The briquette specimens tested in the laboratory also yielded higher rutting
results for the same mix tested in the field. It is therefore important to use specimens that are
most representative of field conditions / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die faktore wat ’n invloed het op die kompakteerbaarheid van warm
asfalt. Faktore sluit in onder andere gradering, vulstof/bindstof verhouding, tipe bindstof,
bindstof inhoud, polimeer modifisering, temperatuuur, volumetriese eienskappe, ens. Hierdie
studie is nie net beperk tot kompakteerbaarheid as ‘n gemete eienskap nie, maar ook die
invloed van hierdie faktore op die mengsel se vermoë om weerstand te bied teen permanente
deformasie of spoorvorming.
’n Eksperimentele ontwerp wat ’n verskeidenheid van bogenoemde faktore insluit is gebruik.
Laboratorium analise van die mengsels asook versnelde plaveisel toetse van die verskillende
tipe mengsels is gedoen met die een-derde skaal Mobiele Lassimuleerder (MMLS3). Die
analise help met die identifikasie van die faktore wat beide kompakteerbaarheid en
spoorvorming beïnvloed, asook dié wat slegs die een maar nie die ander beïnvloed, en ook die
faktore wat geen beduidende invloed het nie. Die kompakteerbaarheid is geëvalueer in terme
van die hol ruimtes in die mengsel by ’n bepaalde bindstof inhoud en verdigtingsgraad.
Spesiale aandag is geskenk aan die eienskappe van die vulstof en vulstof/bindstof
wisselwerking van die mengsels.
Die gradering van ’n mengsel het ’n beduidende invloed op kompakteerbaarheid sowel as
spoorvorming. Hoë vulstof/bindstof verhoudings is een van die kritiese faktore wat die
kompakteerbaarheid van die betrokke mengsels beïnvloed, maar laer vulstof/bindstof
verhoudings vir beter kompaksie het nie ’n beduidende toename in wielsporing teweeg gebring
nie.
Soos verwag het die tipe bindstof ’n beduidende invloed op kompakteerbaarheid sowel as
spoorvorming. ’n Toename in bindstof bevorder verdigting, maar lei tot groter wielsporing.
Polimeer modifisering verminder die wielsporing van ’n standard mengsel onder dieselfde
beladingstoestand. Alhoewel modifisering wielsporing verminder, vereis dit hoër kompaksie
temperature.Die toevoeging van die teenstropingsmiddel GripperL verminder spoorvorming, aggregaat
stroping asook die tempo van spoorvorming van die Kwartsiet LAMBS mengsel as gevolg van
die stropingsmeganisme. Lae digthede kan lei tot aansienlike vogskade en spoorvorming; veral
as die aggregaat vatbaar is vir die invloed van vog.
Daar blyk ’n temperatuur interval te wees waarin verdigting met die Superpave Gyratory
Compactor bereik kan word; maar selfs ‘n klein temperatuurafwyking kan beduidende invloed
op die resultate van spoorvorming hê. Temperatuurbeheer is baie belangrik indien sinvolle
vergelykings tussen die sporingsgedrag van verskillende mengsels gemaak moet word.
Lineêr elasties en eindige element analise is uitgevoer om te bepaal of verskillende
toetskonfigurasies die spanningsverdeling binne die toetsmonsters en die spoorvorming
affekteer. Dit is bevind dat die geometrie van toetsmonsters het ’n invloed op die
spanningsverdeling in die monsters wat die sporingsresultate kan beïnvloed. Die
briketmonsters in die laboratorium gee ook groter spoordiepte teenoor dieselfde mengsel wat in
die veld getoets is. Daarom is dit belangrik om verteenwoordigende monsters te gebruik.
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Numerical (FEA) evaluation of crane end buffer impact forcesHaas, Trevor Neville 12 1900 (has links)
Thesis (PhD (Civil Engineering))--University of Stellenbosch, 2007. / The current codes of practice for the design of structures which were studied during this
investigation do not explicitly account for the flexibilities and interactions of the Electric
Overhead Travelling Crane (EOHTC) and the crane support structure. This leads to analysing
the EOHTC and the gantry structure as a decoupled system for ease of computation. Thus, the
interaction of the various components of the EOHTC and gantry structure is ignored, which may
result in an incorrect assessment of the forces computed in the gantry structure’s members.
This led to a study to determine the effects of a EOHTC on the gantry structure. The research
was conducted through a series of limited experimental tests and extensive advanced Finite
Element Analysis (FEA) simulations.
This resulted in developing a computationally efficient FEA model of the full scale
experimental EOHTC testing facility in the structural engineering laboratory at Stellenbosch
University. The FEA model was developed to conduct simulations for the various load models,
namely, vertical wheel load, horizontal longitudinal load and the horizontal lateral load models,
as prescribed by the various codes. The research was then focussed at determining the
maximum end buffer impact force responses when the crane runs into the end stops. The other
load models were investigated by another researcher using the same FEA model. The results from the experimental tests were used to calibrate the FEA simulations. This proved
exceptionally challenging due to the various structural response phenomena which occur during
the impact of the crane against the end stops. A good correlation between the experimental
values and the values predicted by the FEA simulations was achieved for the first impact.
Modal analysis and modal superposition methods of analysis were used to determine the effect
of the modes of vibration on the structural response to the end buffer impact.
A FEA sensitivity analysis was conducted on a set of identified parameters which have a
significant effect on the structural response to the end buffer impact.
The maximum end buffer impact force was determined for a chosen level of reliability based on
the responses from the sensitivity analysis using the Lagrange Multiplier method.
These maximum end buffer impact forces are then compared with the forces prescribed by the
codes. SABS 0160 slightly underestimates, while SANS 10160 severely overestimates the end
buffer impact force obtained from the constraint optimization technique for a target level of
reliability of β =3.
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Sediment transport dynamics in South African estuariesBeck, Julia S. 12 1900 (has links)
Thesis (PhD (Civil Engineering))--University of Stellenbosch, 2005. / Estuaries are complex water bodies and differ considerably from fluvial river systems. In estuaries the
flow reverses regularly due to the tidal currents and flow depths depend primarily on the tides and not
the flow. An estuary has two sources of sediment: the river during floods and the ocean that supplies
marine sediment through littoral drift which is transported by tidal currents into the estuary.
Oversimplified models cannot be used to investigate the hydrodynamics and geomorphology of an
estuary due to its complexity.
Sedimentation of South African estuaries has created several environmental and social problems.
Sediment transport imbalances have been caused by changes in the river catchments such as increased
sediment yields and flood peak attenuation due to dam construction. Historically floods used to flush
estuaries to maintain the long-term sediment balance in the river-estuary system, but with reduced
flood peaks, sediment transport capacities at the estuaries are reduced and flushing efficiency
decreased, resulting in marine transport dominating in many estuaries.
Two-dimensional (horizontal, 2DH) numerical models have been found to be appropriate tools for
studying hydro- and sediment dynamics in SA estuaries. The modelling shows that the sediment
balance in the estuary relies on a delicate balance between dominant flood and ebb flows. Although
the models performed very well, there are still additional processes to include such as time varying
roughness changes and cohesive sediments. For long-term and long reach simulations, onedimensional
(or quasi-two-dimensional) models will also be required in future.
Mathematical modeling can be used to simulate the flushing of sediments during floods, but attempts
should be made to calibrate these models when adequate field data become available in the future. The
modelling has shown that floods play a very important part in estuarine sediment transport processes.
Physical modelling was undertaken of the breaching of an estuary mouth. The main aim was to
illustrate the merits of breaching at higher water levels as well as to investigate the changes in the
mouth during breaching. The data obtained from the experiments were used to calibrate and verify a
mathematical model. Mathematical modelling of the breaching process at the Klein River estuary
confirms what has been observed during numerous breachings in the field, i.e. that breaching at higher
water levels and towards the southeast side is more effective.
Sediment transport by both waves and currents was investigated. It was found that with increasing
wave and stream power, sediment transport rates would increase if both waves and currents travelled
in the same direction. In contrast, it seems that with the current direction opposing that of the waves,
Hydraulics of Estuarine Sediment Transport Dynamics in South Africa
iii
greater wave heights resulted in lower sediment transport rates. A new sediment transport equation,
based on stream power, wave power, as well as sediment size was calibrated and verified, and
compared to the well-known Bijker formula.
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Risiko-gebaseerde besluitondersteuning in siviele ingenieurswese: 'n metodologiese benadering tot verbeterende inligtingversameling en benuttingBester, Andre 12 1900 (has links)
356 Leaves printed single pages, preliminary pages i-xxii and numbered pages. Includes bibliography. List of tables, list of figures and abbreviations. / Thesis (PhD)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT:Decisions affecting construction projects are often characterised by uncertainty.
One of the sources of this uncertainty is the unit costs used in detail
cost estimates. Analytical techniques are available to model these uncertainties,
but information is required to quantify it. Historical data is the preferred source
of information, but due to unavailability and unreliability it hampers the application
of the analytical techniques. Changes in the construction environment
necessitate the improvement of data sources and the utilisation thereof in a
structured, comprehensive and integrated manner.
The purpose of this study is to determine how decision-making can be improved
by enhanced information capturing and usage of relevant data for
improved cost calculations. This is achieved by investigating the various components
of an information system, viz. dataflow, data source, data application,
and shown how an integrated development of each of these components with
processmodelling, database development and quantitative risk analysis can
lead to improved decision-making. This is achieved by the conceptual redevelopment
and development of information systems for decision support in two
different construction environments, viz. road and dam construction, respectively.
During the research it was found that processmodelling can contribute to the
improvement of dataflow in the fragmented construction environment, but that
shortcomings exist in the processmodelling tools. A method, based on set and
graph theory, was developed to address it. It was also found that database
development provides the opportunity to improve the quality of data stored in
electronic format. A comprehensive database model to store all information
relevant to construction costs, specifications and legal documents with the
required error checking mechanisms was developed. The benefit of modelling
the global uncertainty of project cost estimates with probabilistic techniques
such as Monte Carlo simulation and the Limit State Cost Function, whilst including
the effects of correlation, is also shown.
The information gained from historical data-analysis, besides the application
in the probabilistic techniques, was used to identify properties such as impact,
variability and correlation. It was found in the study that a shortage of descriptive
information, whether it be at project or item level, is predominately the
source of variability in unit cost data after errors have been removed. In order to
identify the information that would contribute to the lowering of variability a
method was developed by using influence factors and unit cost correlation
mechanisms to identify the most influential factors for data capturing. This led to
the development of an ideal data-application model in which all the relevant
data used in the different cost-estimation phases, viz. long term, conceptual and
detail, would be captured and used.
Based on what was found, a generic information system development model
was proposed that indicated the interaction of all the aspects that were investigated.
Two of the model’s foremost properties are its self-triggering process and
incremental development (improvement). On top of this development model a
development process was designed that can be used for the structured, comprehensive
and integrated development/redevelopment of an information
system for cost calculation. / AFRIKAANSE OPSOMMING:Besluite in konstruksieprojekte word gereeld gekenmerk deur onsekerheid.
Een van die bronne van onsekerheid is die eenheidtariewe wat tydens
detailkosteberekeninge gebruik word. Analitiese tegnieke is beskikbaar om die
onsekerhede te modelleer. Inligting word egter benodig om die onsekerhede
mee te kwantifiseer. Die voorkeur bron van inligting is historiese data, maar
weens onbeskikbaarheid en lae akkuraatheid daarvan striem dit die aanwending
van die analitiese tegnieke. Veranderde omstandighede in die
konstruksiebedryf noodsaak egter die verbetering van databronne en aanwending
daarvan op ’n gestruktureerde, omvattende en geïntegreerde wyse.
Die doel van hierdie studie is om te bepaal hoe besluitneming verbeter kan
word deur inligtingversameling en benutting van relevante data vir konstruksiekosteberekeninge
te verbeter. Dit word gedoen deur die onderskeie aspekte
wat deel vorm van ’n inligtingstelsel, nl. die datavloei, datastoring en aanwending
te ondersoek en te toon hoe geïntegreerde ontwikkeling van elk van
hierdie aspekte met behulp van prosesmodellering, databasisontwikkeling en
kwantitatiewe risiko-analise, ’n bydrae kan maak tot verbeterde besluitneming.
Dit word gedoen deur twee verskillende omgewings, nl. padbou en dambou, as
moontlike toepassingsomgewings te gebruik vir onderskeidelik die herontwikkeling
en ontwikkeling van so ’n inligtingstelsel vir besluitneming.
Tydens die ondersoeke is dit gevind dat prosesmodellering ’n waardevolle
bydrae kan lewer tot die verbetering van datavloei in die gefragmenteerde
konstruksie-omgewing, maar dat tekortkominge in die modelleringsprogramme
bestaan. ’n Metode, gebaseer op versameling- en grafiekteorie, is ontwikkel om
hierdie aspekte aan te spreek. Dit is ook gevind dat databasisontwikkeling die
geleentheid bied om die kwaliteit van elektronies gestoorde databronne te
verbeter. ’n Datamodel wat omvattend genoeg is om al die inligting wat met
konstruksiekoste, spesifisering en regsdokumente verbandhou te stoor, is
ontwikkel met die nodige fout-onderskeppingsmeganismes. Die nut van probabilistiese
tegnieke soos Monte Carlo-simulasie en die Limietstaat Kostefunksie
om die globale onsekerheid van projekte se kosteberamings te modelleer en die
effek van korrelasie op die resultate in ag te neem, is ook getoon.
Die inligting afkomstig van historiese data-ontleding, naas die aanwending in
die probabilistiese tegnieke, is gebruik om die eienskappe soos impak, veranderlikheid
en korrelasiemeganismes, te bepaal. Dit is in die studie gevind dat ’n
tekort aan beskrywende inligting, hetsy op projek- of itemvlak, die oorwegende
bron van veranderlikheid is nadat foutiewe data verwyder is. Om egter die
beskrywende inligting te bepaal wat ’n bydrae kan maak tot die verlaging van
hierdie veranderlikheid is ’n metode ontwikkel met behulp van invloedfaktore en
eenheidtariefkorrelasiemeganismes om die mees omvangryke faktore te bepaal
vir onderskepping. Dit het aanleiding gegee tot die ontwikkeling van ’n ideale
data-aanwendingmodel waarin al die relevante inligting vir die verskillende
fases van kosteberekening, nl. langtermyn, konseptueel en detail, onderskep en
gebruik word.
Gebaseer op dit wat gevind is, is ’n generiese inligtingstelsel ontwikkelingmodel
voorgestel wat die interaksie van al die aspekte wat ondersoek is ten
opsigte van mekaar toon. Twee van die hoofkenmerke van hierdie model is die
selfvoerende proses en die inkrementele ontwikkeling van die stelsel. Op hierdie
ontwikkelingmodel is ’n ontwikkelingproses gebou wat gebruik kan word vir
die gestruktureerde, omvattende en geïntegreerde ontwikkeling/herontwikkeling
van ’n inligtingstelsel vir kosteberekeninge.
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Characterisation of model uncertainty for reliability-based design of pile foundationsDithinde, Mahongo 12 1900 (has links)
Dissertation (PhD)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: To keep pace with international trends, the introduction of geotechnical limit state design in
South Africa is inevitable. To pave the way for implementation of limit state pile design in
the country, the study quantifies model uncertainty in the classic static pile design formula
under the Southern African geologic environment. The generated model uncertainty
statistics are used to calibrate partial resistance factors in a reliability-based design
framework.
A series of pile performance predictions by the static formula are compared with measured
performances. To capture the distinct soil types for the geologic region of Southern Africa
as well as the local pile design and construction experience base, pile load tests and
associated geotechnical data from the Southern African geologic environment are used. The
methodology of collecting, compiling, and analyzing the pile load tests to derive the
measured ultimate pile capacities is described. To facilitate the computation of the
theoretical capacities, the site specific geotechnical data in the database are transformed to
the desired engineering soil properties through well established empirical correlations.
For a given pile test case, model uncertainty is presented in terms of a model factor
computed as the ratio of the measured to the theoretical capacity, leading to n realisations of
the model factor. To facilitate further interpretation and generalisation of the model factor
realisation data, statistical analysis is carried out. The statistical analysis comprises of
graphical representation by histograms, outliers detection and correction of erroneous
values, and using the corrected data to compute the sample moments (mean, standard
deviations, skewness and kurtosis) needed in reliability analysis. The analyses demonstrate
that driven piles depict higher variability compared to bored piles irrespective of materials
type. Furthermore, for a given pile installation method (driven or bored) the variability in
non-cohesive materials is higher than that in cohesive materials.
In addition to the above statistics, reliability analysis requires the theoretical probability
distribution for the random variable under consideration. Accordingly it is demonstrated that
the lognormal distribution is the most appropriate theoretical model for the model factor.
Another key basis for reliability theory is the notion of randomness of the basic variables.
To verify that the variation in the model factor is not explainable by deterministic variations
in the database, an investigation of correlation of the model factor with underlying pile
design parameters is carried out. It is shown that such correlation is generally weak. Correlation can have a significant impact on the calculated reliability index if not accounted
for. Accordingly, the effects of the exhibited correlation is investigated through an approach
based on regression theory in which systematic effects of design parameters are taken into
account (generalised model factor). The model factor statistics from the conventional
approach and those from the generalised model factor approach are used to determine
reliability indexes implied by the current design practice. It is demonstrated that no
significant improvement in values of the reliability indexes is gained by taking into account
the effects of the weak correlation.
The model factor statistics derived on the basis of the standard model factor approach are
used to calibrate resistance factors. Four first order reliability methods are employed for the
calibration of resistance factors. These include; the Mean Value First-Order Second
Moment approach, an Approximate Mean Value First-Order Second Moment approach, the
Advanced First-Order Second Moment approach using Excel spreadsheet, and the
Advanced First-Order Second Moment approach (design point method). The resistance
factors from the various calibration methods are presented for the target reliability index
values of 2.0, 2.5, and 3.0. The analyses of the results demonstrate that for a given target
reliability index, the resistance factors from the different methods are comparable.
Furthermore, it is shown that for a given material type, the resistance factors are quite close
irrespective of the pile installation method, suggesting differentiation of partial factors in
terms of materials types only. Finally, resistance factors for use in probabilistic limit state
pile design in South Africa are recommended. / AFRIKAANSE OPSOMMING: Ten einde in pas te bly met internasionale neigings, is dit onafwendbaar dat geotegniese
limietstaat-ontwerp in Suid Afrika ingevoer word. Ter voorbereiding vir die plaaslike
toepassing van limietstaatontwerp op heipale, kwantifiseer hierdie ondersoek onsekerheid
rondom die model vir klassieke statiese heipaalontwerpformules in die Suid Afrikaanse
geologiese omgewing. Die statistiek van modelonsekerheid wat gegenereer is, word
gebruik om parsiële weerstandsfaktore in ’n betoubaarheid-gebasseerde ontwerpraamwerk
te kalibreer.
’n Reeks voorspellings van die gedrag van heipale volgens die statiese formules word
vergelyk met die gemete gedrag. Om die kenmerkende grond-tipes in die geologiese gebied
van Suidelike Afrika sowel as die plaaslike ondervinding met heipaalontwerp en -
konstruksie vas te lê, word heipaaltoetse en die gassosieerde geotegniese data vanuit hierdie
geologiese omgewing gebruik. Die metodiek vir die versameling, saamstelling en analise
van heipaaltoetse om uiterste kapasiteite daarvan te bepaal, word beskryf. Terreinspesifieke
geotegniese data in die databasis word getransformeer na die vereisde ingenieurseienskappe
volgens gevestigde empiriese korrelasies.
Vir ’n gegewe heipaaltoets word modelonsekerheid weergegee in terme van ’n modelfaktor
wat bereken word as die verhouding van die gemete tot die teoretiese kapasiteit waaruit n
uitkomstes van die modelfaktor dus gegenereer word. Om verdere interpretasie en
veralgemening van die modelfaktordata te vergemaklik, word ’n statistiese analise daarop
uitgevoer. Die statistiese analise bestaan uit grafiese voorstellings deur middel van
histogramme, uitkenning van uitskieters en verbetering van foutiewe waardes, waarna die
statistiese momente (gemiddeld, standaardafwyking, skeefheid en kurtose) vir gebruik in
betroubaarheidsanalise bereken word. Volgens die analises toon ingedrewe heipale ’n
groter veranderlikheid as geboorde pale, ongeag die grondtipe. Verder is die
veranderlikheid van heipale in kohesielose materiale hoër as in kohesiewe materiale, ongeag
die installasiemetode (ingedrewe of geboor).
Bykomend tot bogemelde statistiek, vereis betroubaarheidsanalise die teoretiese
waarskynlikheidsdistribusie van die ewekansige veranderlike onder beskouing.
Ooreenkomstig word illustreer dat die log-normale verspreiding die mees toepaslike
verspreiding vir die modelfaktor is. ’n Verdere sleutelvereiste vir betroubaarheidsteorie is die mate van ewekansigheid van die basiese veranderlikes. Om te bepaal of die variasie in
die modelfaktor nie deur deterministiese veranderlikes in die databasis verduidelik kan word
nie, word ’n ondersoek na die korrelasie van die modelfaktor met onderliggende heipaalontwerpfaktore
uitgevoer. Sodanige korrelasie is in die algemeen as laag bevind.
Korrelasie kan ’n belangrike invloed op die berekende betroubaarheidsindeks hê indien dit
nie in ag geneem word nie. Dienooreenkomstig word die effek van die getoonde korrelasie
ondersoek met behulp van die metode van regressie-analise waarin sistematiese effekte van
ontwerpparameters in berekening gebring word (veralgemeende modelfaktor). Die
modelfaktorstatistiek wat volg uit die konvensionele benadering en dié van die
veralgemeende benadering word gebruik om betroubaarheidsindekse te bepaal wat deur die
bestaande ontwerppraktyk geïmpliseer word. Die bevinding is dat daar nie ’n
noemenswaardige verbetering in die waardes van die betroubaarheidsindekse is wanneer die
effek van die swak korrelasie in berekening gebring word nie.
Die statistiek van die modelfaktor wat afgelei is volgens die standaardbenadering word
gebruik om die weerstandsfaktore te kalibreer. Vier eerste-orde betroubaarheidsmetodes
word gebruik om die weerstandsfaktore te kalibreer, naamlik die Gemiddelde Waarde
Eerste-Orde Tweede Moment benadering, die Benaderde Gemiddelde Waarde Eerste-Orde
Tweede Moment benadering, die Gevorderde Eerste-Orde Tweede Moment benadering
waarin ’n Excel sigblad gebruik word en die Gevorderde Eerste-Orde Tweede Moment
benadering (die ontwerppuntmetode). Die weerstandsfaktore vanaf die verskillende
kalibrasiemetodes word weergegee vir waardes van 2.0, 2.5 en 3.0 van die teikenbetroubaarheidsindeks.
’n Ontleding van die resultate toon dat vir ’n gegewe teiken
betroubaarheidsindeks die weerstandsfaktore vanaf die verskillende metodes vergelykbaar
is. Verder word getoon dat vir ’n gegewe grondsoort, die weerstandsfaktore vir verskillende
metodes van installasie van die heipaal nie veel verskil nie. Dit wil dus voorkom asof
parsiële faktore in terme van die grondsoort uitgedruk kan word. Ten slotte word
weerstandsfaktore vir gebruik in plastiese limietstaatontwerp van heipale in Suid Afrika
aanbeveel.
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Reliability modelling of performance functions containing correlated basic variables, with application to construction project risk managementKer-Fox, Gregory Mark 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Correlation mechanisms describing systematic variations and common sensitivities are critical
contributors to uncertainty in quantitative functions modelling project performance in terms
of probabilistic or basic variables. Current reliability methods transform dependent vectors to
an equivalent set of independent standard normal variates. A simple method is developed for
dealing with correlation in the original variable space.
An algebraic description of the direction cosine (or alpha) for performance functions under
conditions of dependence is formally derived and numerically validated. The resultant
General First Order Second Moment (GFOSM) method for correlated basic variables is
shown to be equivalent to the orthogonal transformation method. Geometric and physical
interpretations of the general direction cosine are developed, with alpha found to be
equivalent to the correlation between a basic variable and performance function.
Corresponding inequalities and normalizing conditions are also developed for alpha.
Expressions for a number of applications utilising the general dependent form for the
direction cosine are derived and demonstrated. The current definition of the direction cosine
as an importance factor is validated for dependent conditions, and conditions established
under which this descriptor is no longer adequate. Expressions are derived to measure the
significance of a variable in terms of stochastic importance and function sensitivity, to
establish reliability index sensitivity to the omission of non-critical items, quantifying
variable elasticity and an elasticity index. The general FOSM method for correlated basic
variables is applied to system analysis to generate modal correlation coefficients between
failure modes.
The general direction cosine is stable for multivariate linear functions and functions of limited
curvature across a range of reliabilities and correlation levels. This characteristic further
simplifies the process by providing for deterministic reliability modelling of performance
functions containing dependent variables, avoiding the solution of the more complex joint
density function.
The extension of the current theory and the treatment of performance functions in the original
vector space develop invaluable insight into the correlation mechanisms driving risk and
reliability. This will assist project managers to better understand areas that can affect project
performance, to focus management attention, develop mitigation strategies and to allocate
resources for the optimal management of project risk. / AFRIKAANSE OPSOMMING: Korrelasie meganismes wat sistematiese afwykings en gemeenskaplike sensitiwiteite
veroorsaak, is kritieke bydraers tot onsekerheid in kwantitatiewe funksies wat projek prestasie
modelleer m terme van probabilistiese of basiese veranderlikes. Huidige
betroubaarheidsmetodes transformeer afhanklike vektore tot 'n ekwivalente stel van standaard
normaalonafhanklike veranderlikes. '0 Eenvoudige metode is ontwikkelom die effekte van
korrelasie in die oorspronklike vektorspasie te hanteer.
'n Algebraise beskrywing van die rigtingseosines (genoem alfa) vir prestasiefunksies onder
omstandighede van afhanklikheid is formeel afgelei en numeries gevalideer. Dit is bewys dat
die resulterende Algemene Eerste Orde Tweede Moment metode vir gekorreleerde basiese
veranderlikes ekwivalent is aan die tradisionele Ortogonale Transformasie metode.
Geometriese en fisiese interpretasies vir die algemene rigtingscosinus is ontwikkel, met
bewys dat alfa ekwivalent is aan die korrelasie tussen 'n basiese veranderlike en die
prestasiefunksie. Ooreenstemmende ongelykhede en normaliserings-kondisies is ook vir alfa
ontwikkel.
Uitdrukkings vir 'n aantal toepassings wat gebruik maak van die algemene afhanklike vorm
van die rigtingscosinus is afgelei en gedemonstreer. Die huidige definisie van die
rigtingscosinus as 'n belangrikheidsfaktor is gevalideer vir kondisies van afhanklikheid en
omstandighede is uitgewys wanneer dit onvoldoende is. Uitdrukkings is afgelei om
stochastiese belangrikheid te meet asook funksie sensitiwiteit, die sensitiwiteit van die
betroubaarheidsindeks tot die weglating van nie kritiese veranderlikes, sowel as die
kwantifisering van elastisiteit en die elastisiteitsindeks. Die Algemene Eerste Orde Tweede
Moment metode vir gekorreleerde' veranderlikes is toegepas op sisteem analise om die
korrelasie tussen falingsmodes te genereer.
Die algemene rigtingscosinus is stabiel vir liniêre funksies en funksies met 'n beperkte
kromming oor 'n reeks betroubaarheidswaardes en korrelasie vlakke. Hierdie kenmerk
vereenvoudig die metode verder deur voorsiening te maak vir deterministiese
betroubaarheidsmodellering van prestasie funksies met afhanklike veranderlikes, deur die
oplossing van die meer komplekse gesamentlike-digtheidsfunksies te vermy.
Die uitbreiding van die huidige teorie en die hantering van prestasie funksies in die
oorspronklike vektor spasie ontwikkel waardevolle insig in die korrelasie meganismes wat
risiko en betroubaarheid oorheers. Hierdie insig sal projekbestuurders in staat stelom kritieke
gebiede wat projek prestasie kan affekteer beter te verstaan, om hulle aandag daarop te fokus,
om teenmaatreël-strategieë te ontwikkel en hulpbronne toe te ken vir die optimale bestuur van
projek risiko.
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