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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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A contribution to the advancement of geotechnical engineering in South AfricaDay, Peter William 03 1900 (has links)
Thesis (DEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Geotechnical engineering is a relatively young field of engineering and one in which there are
still many unanswered questions and gaps in our knowledge. Added to this, the geotechnical
materials on each new site on which geotechnical work is undertaken are the unique product of
many influences including geology, geomorphology, climate, topography, vegetation and man.
There is thus plenty of scope for innovation.
This dissertation describes the contributions made to Geotechnical Engineering in South Africa
by the Candidate over a period of close on 40 years. It describes the three-step process
followed in the majority of these contributions. Step one is the identification of a problem that
requires investigation, the application of new techniques or simply the consolidation of existing
knowledge. Step 2 is the investigation of the problem and the development of a solution. Step
3 is sharing the outcome of this work with the profession by means of publications, by
presentations at seminars and conferences or by incorporation into standards / codes of
practice.
Part 1 of the dissertation describes the exciting environment in which geotechnical engineers
operate. This environment is characterised by openness and cooperation between practitioners
of geotechnical engineering, be they geotechnical engineers, engineering geologists,
contractors, suppliers or academics. This part also explores the parallels in the roles played by
academics and practitioners and how each can contribute to the advancement and
dissemination of knowledge. Part 2 describes contributions made in various fields including
problem soils (dolomites, expansive clays, uncompacted fills, etc.), lateral support, pile design
and construction, health and safety, and cooperation with international organisations. Part 3
describes the Candidate's involvement in the introduction of limit states geotechnical design into
South African practice culminating in the drafting of SANS 10160-5 on Basis of Geotechnical
Design and Actions. It also describes the Candidate's work with the ISSMGE Technical
Committee TC23 dealing with limit states design. Part 4 deals with the Candidate's contribution
to other codes and standards and his role on various committees of the Engineering Council of
South Africa and the South African Bureau of Standards.
The final part of the dissertation provides an overview of the process followed in making such
contributions, highlighting the role played by curiosity and a desire to share the knowledge
gained with others in the profession. It continues by identifying work that still needs to be done
in many of the areas where contributions have been made and concludes with a statement of
what the candidate would still like to achieve during the remainder of his career. The Candidate gratefully acknowledges the generous opportunities afforded to him by his
colleagues at work and the invaluable guidance and mentorship received from fellow
professionals in academia and practice. / AFRIKAANSE OPSOMMING: Geotegniese ingenieurswese is 'n relatiewe jong wetenskap en een met vele kennisgapings en
waarin daar nog talle vrae onbeantwoord bly. Daarby is geotegniese materiale uniek tot elke
terrein waarop werk aangepak word en die produk van 'n kombinasie van prosesse; insluitend
geologie, geomorfologie, klimaats toestande, topografie, plantegroei en menslike aktiwiteite.
Daar is dus nog ruim geleentheid vir innoverende bydraes.
Hierdie verhandeling beskryf die Kandidaat se bydraes tot Geotegniese Ingenieurswese in
Suid-Afrika oor die afgelope 40 jaar. Dit beskryf 'n drie-voudige benadering wat in die meeste
van die bydraes gevolg is. Die eerste stap is om die probleem te definieer en te omskryf in
terme van die ondersoek wat geloods moet word, asook die noodsaaklikheid vir die
ontwikkeling van nuwe tegnologie teenoor die konsolidasie van bestaande inligting. Tydens die
tweede stap word die probleem ondersoek en 'n oplossing ontwikkel. Die derde stap is om die
resultate te deel met die geotegniese bedryf by wyse van publikasies, voorleggings by
konferensies en seminare, en insluiting in praktykkodes en standaarde.
Deel 1 beskryf die opwindende werksomstandighede waarbinne geotegniese ingenieurs hul
bevind. Dit word geken aan die ope samewerking tussen belanghebbende partye; onder
andere ingenieurs, ingenieursgeoloë, kontrakteurs, verskaffers en akademici. Deel 1
beklemtoon ook die parallelle rolle wat vertolk word deur akademici en praktiserende ingenieurs
en hoe beide partye bydraes maak tot die ontwikkeling en verspreiding van tegnologie. Deel 2
beskryf die Kandidaat se bydraes tot verskeie navorsingsvelde; waaronder probleemgrondtoestande
(dolomiet, swellende kleie, ongekonsolideerde opvullings ens.), laterale
ondersteuning, ontwerp en konstruksie van heipale, beroepsveiligheid, en samewerking met
internasionale organisasies. Deel 3 beskryf die Kandidaat se betrokkenheid by die
bekendstelling van limietstaat geotegniese ontwerp in die Suid-Afrikaanse bedryf wat uitgeloop
het op die samestelling van SANS 10160-5 Basis of Geotechnical Design and Actions. Dit
beskryf ook die Kandidaat se samewerking met die ISSMGE Technical Committee TC23 wat te
make het met limietstaat ontwerp. Deel 4 beskryf die Kandidaat se bydraes tot ander kodes en
standaarde en die rolle wat hy vertolk het op verskeie komitees van die Suid-Afrikaanse Raad
vir Ingenieurswese asook van die Suid-Afrikaanse Buro van Standaarde.
Die laaste deel van die verhandeling bied „n oorsig oor die proses wat gevolg is in bostaande
bydraes met die klem op die rol van weetgierigheid en die begeerte om sulke kennis te deel met
ander belanghebbendes. Om af te sluit, identifiseer die Kandidaat oorblywende tekortkominge
in baie van die vraagstukke waar hy bydraes gelewer het en gee 'n opsomming van wat hy
graag nog sal wil bereik tydens die verdere verloop van sy loopbaan. Die Kandidaat gee met dank erkenning aan sy kollegas vir die ruim geleenthede wat hom
gebied is en die waardevolle leiding en mentorskap wat hy ontvang het van mede praktiserende
ingenieurs en akademici.
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Mechanical and structural characterisation of extrusion moulded SHCCVisser, Christo Riaan 12 1900 (has links)
Thesis (MScIng)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: SHCC (Strain-Hardening Cement-based Composite) is a type of HPFRCC (High Performance Fibre
Reinforced Cement-based Composite) that was designed and engineered to overcome the
weaknesses of ordinary concrete. It shows a high ductility as it can resist the full tensile load at a
strain of more than 3%. This superior response is achieved with multiple cracking under tensile
loading which has a pseudo strain-hardening phenomenon as a result.
The purpose of the research project reported in this thesis document was to design and build a new
piston-driven extruder for the production of SHCC as well as R/SHCC (reinforced SHCC) elements
and to investigate and characterise the structural and mechanical behaviour of extrusion moulded
SHCC.
A new piston-driven extruder, specifically for academic purposes, was designed based on the
principles of fluid flow mechanics. Although fluid flow is not an ideal model to represent the flow
of viscous material through an extruder, it was deemed sufficient for this specific study. A new
extruder with the capacity to extrude SHCC and R/SHCC was built. Provision was made that this
extruder can be fitted with extruder dies and transition zones of varying shapes and sizes.
A comparative study between unreinforced as well as reinforced cast SHCC and extruded SHCC as
well as a suitable R/C (Reinforced Concrete) was conducted. Three-point bending tests,
representative of the envisioned structural application, were performed on specimens of each of the
composites.
The unreinforced cast SHCC and especially the unreinforced extruded SHCC have a comparative
level of performance to the cast R/C. These specimens displayed a similar cracking pattern of
multiple cracks, although less pronounced in the extruded SHCC. The extruded SHCC has superior
first cracking and ultimate strength in comparison to cast SHCC, but with accompanying lower
ductility.
The reinforced SHCC specimens failed in a combination of flexure and shear. The extruded
R/SHCC specimens formed multiple diagonal cracks before failure, while the cast R/SHCC
specimens formed only a few diagonal cracks, before delaminating along the reinforcement. The
higher shear capacity and thus the ability to form multiple diagonal cracks of the extruded R/SHCC can be ascribed to the better fibre orientation of the specimens in the longitudinal direction, while
the cast specimens have a random orientation of fibres. R/SHCC and especially extruded R/SHCC
could be a far superior structural material to R/C.
Mechanical characterisation of extruded SHCC was done with the use of uni-axial tensile and
compressive tests. The results of these tests were compared with the results of uni-axial tensile tests
previously performed on cast SHCC as well as uni-axial compressive tests that were performed on
cast SHCC in this research study.
The extruded SHCC displayed superior tensile performance in terms of first cracking and ultimate
strength in comparison to cast SHCC, but with accompanying lower ductility. In terms of
compressive performance the extruded SHCC has a higher ultimate strength, but with a lower
ductility than cast SHCC. The extruded SHCC also has a much higher E-modulus than cast SHCC.
This can partly be attributed to the difference between the water/binder ratios of the cast and
extruded SHCC, but can mainly be ascribed to the lower porosity as a result of high extrusion forces
involved in the manufacturing of extruded SHCC.
A simple bending model for SHCC has also been introduced. This model is based on the
mechanical characteristics of SHCC. The model somewhat underestimates the resistance moment of
the extruded and cast SHCC, but this underestimation is more pronounced in the case of the cast
SHCC. Various reasons for the underestimation is discussed, but it is postulated that the main
reason for the difference in experimentally determined and the calculated resistance moment of the
cast SHCC is the possible variation in ingredient properties and specimen preparation and testing,
since the characterisation of the cast SHCC was done over a long period of time and by different
researchers. The bending model is however deemed sufficient for the design purposes of SHCC. / AFRIKAANSE OPSOMMING: SHCC (“Strain-Hardening Cement-based Composite”) is ‘n tipe HPFRCC (“High Performance
Fibre Reinforced Cement-based Composite”) wat ontwerp is om die swakhede van gewone beton te
oorkom. Hierdie materiaal het ‘n hoë duktiliteit en kan die volle trekkrag weerstaan met ‘n
vervorming van meer as 3%. Hierdie uitstaande gedrag word gekenmerk deur meerdere krake wat
vorm gedurende ‘n trek belasting wat vervormingsverharding tot gevolg het.
Die doel van die navorsingsprojek wat weergegee word in hierdie tesis dokument was om ‘n nuwe
suier-aangedrewe ekstrueerder vir die produksie van SHCC sowel as R/SHCC (bewapende SHCC)
te ontwerp en te bou en om die strukturele en meganiese gedrag van ge-ekstrueerde SHCC te
ondersoek en te karakteriseer.
‘n Nuwe suier-aangedrewe ekstrueerder, spesifiek for akademiese doeleindes, is ontwerp gebaseer
op die beginsels van vloeistof vloeimeganika. Alhoewel vloeistof vloeimeganika nie ‘n ideale
model is vir die voorstelling van die vloei van ‘n viskose materiaal deur ‘n ekstrueerder nie, word
dit beskou as aanvaarbaar vir die doeleindes van hierdie spesifieke studie. ‘n Nuwe ekstrueerder
met die kapasiteit om SHCC en R/SHCC te ekstrueer is gebou. Voorsiening is ook gemaak dat
ekstrueerder vorms (“dies”) en oorgangsones van verskillende vorms en groottes aan die
ekstrueerder geheg kan word.
‘n Vergelykende studie tussen onbewapende sowel as bewapende gegote en ge-ekstrueerde SHCC,
sowel as ‘n gepasde R/C (“Reinforced Concrete”) is uitgevoer. Drie-punt buigtoetse,
verteenwoordigend van die voorgestelde strukturele toepassings vir SHCC, is uitgevoer op
proefstukke van elk van die bogenoemde materiale.
Die meganiese gedrag van die onbewapende gegote SHCC en spesifiek die onbewapende geekstrueerde
SHCC is vergelykbaar met die meganiese gedrag van gegote R/C. Hierdie proefstukke
het ooreenstemmende kraakpatrone van veelvuldige krake getoon, alhoewel dit minder prominent
was in die geval van ge-ekstrueerde SHCC. Die ge-ekstrueerde SHCC het hoër eerste kraak- en
maksimum sterktes in vergelyking met gegote SHCC, maar met gepaardgaande laer duktiliteit.
Die bewapende SHCC proefstukke het in ‘n kombinasie van buig en skuif gefaal. Die geekstrueerde
R/SHCC proefstukke het meerdere diagonale krake gevorm voor faling, terwyl die
gegote R/SHCC proefstukke slegs ‘n paar diagonale krake gevorm het, voordat dit langs die bewapening gedelamineer het. Die hoër skuifkapasiteit van ge-ekstrueerde SHCC en dus die
vermoë om meerdere diagonale krake te vorm, kan toegeskryf word aan die longitudinale orientasie
van vesels van die proefstukke, terwyl gegote proefstukke se vesels meer lukraak georienteerd is.
R/SHCC en spesifiek ge-ekstrueerde R/SHCC kan‘n superieure strukturele materiaal in vergelyking
met R/C wees.
Die meganiese karakterisering van ge-ekstrueerde SHCC is gedoen met die gebruik van direkte
trek- en druktoetse. The resultate van die hierdie toetse is vergelyk met die resultate van direkte
trektoetse uit ‘n vorige studie op gegote SHCC,, sowel as met die uitslae van direkte druktoetse wat
op gegote SHCC in hierdie navorsingstudie gedoen is.
Die ge-ekstrueerde SHCC het superieure trekgedrag in terme van eerste kraak en maksimum
sterktes in vergelyking met gegote SHCC getoon, maar met gepaardgaande laer duktiliteit. In terme
van drukgedrag het die ge-ekstrueerde SHCC ‘n hoër maksimum druksterkte, maar met ‘n laer
duktiliteit in vergelyking met die gegote SHCC. Die ge-ekstrueerde SHCC het ook ‘n veel hoër Emodulus
as gegote SHCC. Dit is gedeeltelik as gevolg van die verskil in die water/binder
verhouding van die gegote en ge-ekstrueerde SHCC, maar kan grootliks toegeskryf word aan die
laer porositeit van ge-ekstrueerde SHCC as gevolg van die hoë ekstrusie kragte.
‘n Eenvoudige buigmodel vir SHCC word ook voorgestel. Hierdie model is geabseer op die
meganiese gedrag van SHCC. Die model onderskat die weerstandsmoment van ge-ekstrueerde
SHCC sowel as gegote SHCC, maar hierdie onderskatting is meer prominent in die geval van
gegote SHCC. Verskeie redes vir hierdie onderskatting word genoem, maar dit word beweer dat in
die geval van gegote SHCC dit grootliks as gevolg van moontlike variasies in die materiaal
eienskappe en proefstukke se voorbereiding en toetsing is, aangesien die karakterisering van die
gegote SHCC oor ‘n lang tydperk en deur verskillende navorsers gedoen is. Die buigmodel word
nogtans as voldoende beskou vir die ontwerpdoeleinde van SHCC.
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Best practice of crane support structures design : an expert surveyThompson, Geoffrey 12 1900 (has links)
Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2007. / Research on cranes and crane support structures has been completed at Stellenbosch University’s
Structural Division. In order to link the research already completed with that which is practically
relevant, an industry related expert survey was proposed. Consequently, the research title is “Best
Practice of Crane Support Structures Design – An Expert Survey”.
The primary objective of the study is to complete research, which can be used at a later stage to
compile a “best practice” guideline for support structures design. The expert survey allows
practical experience and opinion to be gathered from experts. The primary drawback being the
uncertainty involved in such opinionated research material. For this reason an attempt is made in
the thesis to apply a scientific approach, in order to attain rationally defendable results.
The survey was conducted using interviews with experienced crane support structure designers and
crane manufacturers in South Africa. The experts were then rated according to their answers to
seeded questions, the number of colleague recommendations they each received and the years of
experience each expert has. The expert opinion was subsequently combined using the expert
ratings as weights. To further improve the scientific rationale behind the results, several of the
topics mentioned by the experts were verified using related literature - thereby validating the use of
the combined expert opinion for this research.
The results obtained from the survey and verification process are regarded as useful to the
objectives of the study. Information concerning pre-design specifications, loads and actions,
structural analysis, design, design details and fatigue was compiled. The direct results are tabulated
in an appendix and commentary, based on the expert opinions, is provided.
A failure investigation was also completed with less success than initially intended. This was due,
in part, to confidentiality issues and a lack of failure information easily accessible to the experts.
For this reason the results of the failure investigation focuses more on various failure mechanisms. The success of the survey indicates that expert opinion is a useful tool for research. Furthermore,
the minor differences in expert opinion, when compared to information obtained from crane support
structure literature, indicates that the expertise in the South African crane support structure design is
at an international standard.
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An experimental investigation into the behaviour of a 5 ton electric overhead travelling crane and its supporting structureDe Lange, Johan Hendrik 03 1900 (has links)
Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2007. / In structural engineering practice the actions imposed by overhead travelling cranes onto the
supporting structure are defined as static forces amplified by dynamic coefficients and applied as
pseudo-static forces without taking the interaction between crane and supporting structure into
account.
To investigate the validity of this approach, the forces generated at the wheels of an experimental
crane are measured, as the crane traverses on the supporting structure. The interaction at the wheels
of the crane is also visually recorded. These wheel load results will also be used by other
researchers, to calibrate a numerical model of the experimental system.
A full-scale 5 ton electric overhead travelling crane (EOTC) running on top of rails and a
supporting structure, was designed and erected for research purposes. The crane has a span of 8.3 m
and wheel spacing of 4 m, which can be modified. The supporting structure consists of three simply
supported mono-symmetric plate girders on each side, with a total length of 13.8 m. This is
supported by columns with a height of about 3.5 m. This paper describes the calibration of this
system for measurement purposes.
A data acquisition system was implemented to capture forces, strains, deflections and accelerations
at various points on the crane and the supporting structure as well as to measure the velocity of the
crane. The forces at the crane wheels are measured through strain gauges on the end carriage load
measuring system.
The calibrated facility is used to investigate the behaviour of the crane and the supporting structure
under regular and exceptional wheel loads, which are classified as follows:
- Regular wheel loads occur during normal payload hoisting and lowering, longitudinal
crane travel with payload and lateral crab travel with payload.
- Exceptional wheel loads occur during eccentric payload hoisting (payload outside normal
operational area), impact forces on end-stops, maximum hoisting of the payload, failure of a
longitudinal drive mechanism of the crane, misalignment of the supporting structure and
skewing of the crane.
The maximum values of these experimentally determined wheel loads and the dynamic response of
the system is used to help describe the behaviour of the electric overhead travelling crane and its
supporting structure.
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Development of provisional guidelines for the treatment of scale and resolution in assessing streamflow reduction impacts of alien plant infestations and commercial afforestation in water resources modelling studiesDzvukamanja, T. N. (Tembiwe Nunana) 12 1900 (has links)
Thesis (MScEng)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Experiments conducted on afforested catchments in South Africa have shown that alien trees
can cause substantial reductions in catchment runoff (Scott et ai, 2000).
In recognition of the impact which alien trees can have on the country's water resources,
commercial afforestation was declared a stream flow reduction activity (SFRA) in terms of
the National Water Act (NW A) (No. 36 of 1998), and the Department of Water affairs and
forestry launched the Working for Water Programme (WfW) in 1995 with the recovery of
water resources lost to Invasive alien plants (lAPs) as one of the Programme's objectives.
These initiatives have intensified the need to quantify SFR; for example, for licensing
purposes to satisfy the requirements of the NWA and for predicting the effects of lAP clearing
by WfW projects. Of interest to water resources practitioners, is the impact of SFR on mean
annual runoff (MAR), on low flows and on water resource system, or reservoir, yield.
In South Africa two basic methods of streamflow reduction (SFR) estimation have been
developed for commercial afforestation and lAPs. These are
• free-standing empirical relationships in the form of the CSIR SFR CUNes, used in
conjunction with the monthly, calibration-based, Pitman model.
• component modules in the physically-based, land-use sensitive ACRU rainfall-runoff
catchment model, run at a daily time step with relatively fine subcatchment delineation.
There has been a strong need for an evaluative comparison of the impacts of SFR estimated
via these two methods. This study aimed to meet this need by using both methods to
estimate SFR for a number of commercial afforestation and lAP scenarios in three study
systems, the Berg, Sabie and Mhlatuze, representing different bioclimatic conditions in South
Africa, and running the SFR sequences from the two estimation methods through the Water
Resources Yield Model to determine the impact of the SFR on yield. The analysis
differentiated between upland and riparian SFR, and between SFR produced by different tree
classes.
Study conclusions included the following points:
• Both the ACRU and SHELL models are capable of achieving a reasonable average
seasonal correspondence of high and low flows with the observed averages, though the
actual averages produced by the two models can differ substantially. In general, ACRU simulates less SFR than SHELL, and gains in SFR after afforestation
or invasion by lAPs may be simulated by ACRU during dry periods. The selection of crop
factors for different plant species has a strong influence on the relative water use of the
species modelled in ACRU.
• The impacts on yield of SFR due to lAPS and afforestation tends to be greater than the
impact on MAR, and impacts tend to be more severe for small subcatchments than for
the total catchment. A simulated reduction in MAR can result in a simulated increase in
yield of a given assurance, if the portion of the flow sequence occurring during the critical
period is dominated by streamflow gains, and vice versa.
Research recommendations centred on improving the availability of reliable field
measurements of parameters and processes required tor the effective modelling of SFR.
Based on the results of the study, guidelines were formulated for SFR modelling, focussing
on the choice of SFR estimation method and the treatment of various parameters and
considerations which influence the outcomes of SFR modelling. / AFRIKAANSE OPSOMMING: Eksperimente wat in bebosde opvanggebiede in Suid-Afrika uitgevoer is, het getoon dat
uitheemse bome aansienlike verminderings in opvanggebied-afloop kan veroorsaak (Scott et
al,2000).
Ter erkenning van die impak wat uitheemse bome op die land se waterbronne kan he, is
kornrnersiele bebossing verklaar as 'n stroomvloei-verminderingsaktiwiteit (SVVA) in terme
van die Nasionale Waterwet (NWW) (Nr. 36 van 1998). Die Departement van Waterwese en
Bosbou het ook die Werk-vir-Water Program (WvW) in 1995 geloods met, as een van die
doelwitte, die herwinning van waterbronne wat deur uitheemse indringerplante (UIPe)
opgebruik word. Hierdie inisiatiewe het die behoefte om SVV te kan kwantifiseer verskerp;
by voorbeeld; for liksensiermqsdoeleindes om die vereistes van die NWW te bevredig, of om
die impakte van UIP-opruiming in WvW-projekte te voorspel. Van besondere belang vir
waterbron-praktisyns is die impak van SVV op gemiddelde jaarliks afloop (GJA), op lae
vloeie en op die lewering van waterbronne, of -stelsels.
In Suid-Afrika is twee basiese metodes vir SVV-raming ontwikkel vir komrnersiele bebossing
en UIPe, soos volg:
• losstaande empiriese verbande in die vorm van die WNNR se SVV-krommes, wat
gebruik word saam met die maandelikse, kalibrasie-gebaseerde, Pitman-model wat in die
SHELL-sagteware-omgewing ingebou is.
• Modules wat komponente vorm in die fisies-gebasserde, grondgebruik-gevoelige ACRU
reenval-atloop opvanggebiedmodel, wat op 'n daaglikse tydstap loop, met relatiewe fyn
subopvanggebied-indelings.
Daar bestaan al lank 'n sterk behoefte aan 'n takserende vergelyking van die impakte van
SVV so os geraam via hierdie twee metodes. Hierdie navorsing het beoog om hierdie
behoefte te bevredig deur beide metodes in 'n aantal kornrnersiele bebossings- en UIPscenario's
in drie stelsels, die Berg, Sabie en Mhlatuze, te gebruik. Sodoende word drie
verskillende bio-klimaatstreke gedek. Die maandelikse SVV-tydreekse van die twee
ramingsmetodes was toe ingevoer in 'n waterbronstelselmodel (WRYM) om die impak van
die SVV op die lewering te bepaal. Die ontledings het tussen oewer- en nie-oewer-SVV,
asook tussen SVV wat deur verskillende boom-klasse veroorsaak is, onderskei.
Die gevolgtrekkings uit die studie het die volgende punte ingesluit: • Seide die ACRU- en SHELL-modelle is in staat om 'n redelike ooreenkoms in seisoenale
hoe en lae vloeie met waargenome gemiddeldes te verskaf, alhoewel die eintlike
gemiddeldes wat deur die twee modelle gelewer word, aansienlik kan verskil.
• Oor die algemeen simuleer ACRU laer SVV as SHELL en klein toenames in vloeie na
bebossing of indringing deur UIPe kan soms tydens droe tydperke deur ACRU
gesimuleer word. Die keuse van gewasfaktore vir verskillende planttipes het 'n groot
invloed op die relatiewe waterverbruik van die planttipes wat in ACRU gemodelleer word.
• Die impakte op lewering van SVV te wyte aan beide UIPe en bebossing neig om groter te
wees as die impak op GJA, en die impakte neig om meer ernstig te wees vir klein
subopvanggebiede as vir die totale opvanggebied. 'n Gesimuleerde vermindering in GJA
kan soms saamval met 'n gesimuleerde toename in lewering teen 'n spesifieke
betroubaarheid, as die gedeelte van die tydreeks wat gedurende die kritieke tydperk
voorkom, heelwat UIP-gebaseerde stroomvloei-toenames bevat en vice versa.
Navorsingsaanbevelings fokus op die verbetering van die beskikbaarheid van betroubare
veldwaarnemings van parameters en prosesse wat vereis word vir betroubare modellering
van SVV.
Riglyne vir SVV-modellering is geformuleer, gebaseer op die resultate van hierdie navorsing,
met 'n fokus op die keuse van SVV-ramingsmetode, die behandeling van verskeie
parameters en oorwegings wat die uitslag van SVV-modellering sou kon bemvloed.
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Reliability of reinforced concrete shear resistanceHuber, U. A. 12 1900 (has links)
Thesis (MScEng)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: The lack of a simple rational mechanical model for the shear resistance behaviour of structural concrete
members results in the use of simplified empirical methods in codified shear design methods with a
limited range of applicability. This may lead on the one hand to insufficient reliability for members on
the boundary of the range of applicability and on the other hand to over-conservative designs.
Comparison of the provision for shear resistance design of the South African code of practice for the
design of concrete structures SANS 10100: 2003 with other related codes shows differences in the
design variables taken into account and procedures specified to calculate shear resistance.
The thesis describes a systematic evaluation of the reliability performance of the shear performance of
reinforced concrete sections subjected to shear only, and in combination with flexural moments,
designed with SANS 10100: 2003. Both sections with and without provision for shear reinforcement
are considered. A representative range of parametric conditions are considered in the evaluation.
Punching shear is not considered in the present review.
Shear design as specified by SANS 10100 is compared to the provisions of the closely related British
code for the structural use of concrete BS 8110, Eurocode 2 for the design of concrete structures EN
1992 and the American bridge design code AASHTO LRFD.
The reliability performance of the shear design method for beams of SANS is considered in terms of a
probabilistic shear resistance model, uncertainties in the basic variables such as material properties,
geometry and modelling uncertainty. Modelling uncertainty is determined by comparing predicted
values with published experimental results.
Keywords: structural concrete; shear resistance; shear design; reliability; design codes; code
companson / AFRIKAANSE OPSOMMING: Die tekortkoming van eenvoudige rasionele modelle vir skuif gedrag van strukturele gewapende beton
lei tot die gebruik van vereenvoudigde empiriese metodes in gekodifiseerde skuif ontwerp met 'n
beperkte omvang van gebruik. Dit mag lei tot onvoeldoende betroubaarheid vir ontwerp situasies, maar
ook tot oorkonserwatiewe ontwerpe. Vergelyking van voorsienings vir skuifweerstand ontwerp in die
SANS beton kode, SANS 10100: 2003 en ander verwante kodes toon verskille in ontwerp veranderings
en metodes aan vir die berekening van skuifweerstand.
Hierdie tesis beskryf die stelselmatige bepaling van betroubaarheids prestasie van die skuifgedrag van
gewapende beton snitte ontwerp volgens SANS. Beide snitte met en sonder skuifbewapening word
behandel. 'n Verteenwoordigende bestek van skuif ontwerp parameters word in ag geneem in die
beoordeling van die betroubaarheid. Pons skuifword nie hier in ag geneem nie.
Skuif ontwerp soos voorgeskryf deur SANS 10100 word verlyk met die ontwerp methodes van die
Britse beten kode, BS 8110, die Europese beton kode, Euronorm Eurocode 2 en die Amerikaanse brug
kode AASHTO LRFD.
Die betroubaarheids prestasie van die skuif ontwerp metode vir SANS word bepaal deur middel van 'n
probablistiese skuif ontwerp model. Modelonsekerheid is vir die doeleindes bepaal deur vergelyking
met gepubliseerde eksperimentele resultate.
Sleutelwoorde: strukturele beton; skuifweerstand; skuif ontwerp; betroubaarheid; ontwerp kodes; kode
vergelyking.
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The rating of compound sharp-crested weirs under modular and non-modular flow conditionsCanto, R. R. 03 1900 (has links)
Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: The compound sharp-crested weir, which consists of two or more notches at different
elevations, is the most common type of flow gauging structure found in South Africa. The
Department of Water Affairs and Forestry (DWAF) is responsible for the operation of these
weirs. They are currently experiencing the following problems regarding flow measurement
with compound sharp-crested weirs:
1. During free-flow conditions, also known as modular flows, there is uncertainty about the
accuracy of the discharge formulas. Although reliable formulas exist for single notch weirs,
it is not clear how they should be modified for compound weirs. Whilst methods have
already been developed to deal with compound weirs their accuracy needs to be investigated
further.
2. When the weirs become submerged during floods, the upstream water head is affected by
downstream water levels and the original formulas are not applicable. It has so far been
impossible to calculate discharge accurately under these so-called non-modular flow
conditions.
This report summarises the findings of an extensive study which addressed the issues mentioned
above. A comprehensive test programme was completed during which variations of compound
sharp-crested weirs were tested under both modular and non-modular flow conditions. In the
development of new methods care was taken to adhere to internationally accepted standards.
This should make South African practice acceptable to others.
One important characteristic of compound weirs is the presence of end contractions. It was
found that they have a significant effect on discharge measurement. Generally, the more a weir
is contracted, the lower its coefficient of discharge becomes. It was also established that end
contractions can ensure excellent aeration for compound weirs.
For modular flow conditions it was possible to develop a discharge formula based on the IMFf
equation, which is included in the ISO standards. This new method was found to produce the
smallest errors when compared to other existing formulas (average error 0.6%).
During non-modular flow conditions it was noted that end contractions also play an important
role, at least during the early stages of submergence. In full-width weirs the upstream water
level tends to drop first (due to de-aeration) before it rises again with increasing submergence.
Weirs with end contractions do not suffer from this problem.
It was further established that the effect of submergence could be described in terms of an
energy loss occurring at the drowned weir. This energy loss is a function of the velocities at the
so-called vena contracta of the weir and at the downstream river cross section. As the
difference between these velocities increases, the energy loss increases as well.
Two methods were tested to estimate the discharge under submerged conditions. The
Villemonte formula works well if the energy losses at the weir are relatively high, while the
Wessels method is reliable if the energy losses become smaller. A procedure was developed
which indicates when each method is applicable. The test data indicated that the maximum
error is up to ±10% at high submergence ratios (S> 0.80) if this procedure is followed. / AFRIKAANSE OPSOMMING: Multikeep-skerpkruinmeetstrukture bestaande uit twee of meer kepe op verskillende vlakke
word meestal gebruik om vloeie in Suid-Afrikaanse riviere te meet. Die Departement van
Waterwese en Bosbou (DWAF) is verantwoordelik vir die instandhouding van sulke
meetstrukture. Hulle ervaar tans die volgende probleme met vloeimeting by multikeepskerpkruine:
1. Gedurende modulêre (onversuipte) toestande bestaan daar nog onsekerheid oor die
akkuraatheid van die formules wat gebruik word om vloeitempo's te bereken. Alhoewel
betroubare formules ontwikkel is vir enkelkepe, is dit nie duidelik hoe hulle aangepas kan
word sodat hulle ook vir multikepe gebruik kan word nie. Die akkuraatheid van sommige
bestaande metodes vir multikepe moet ook ondersoek word.
2. Onder versuipte toestande word die stroom-op watervlak beïnvloed deur die stroom-af
watervlak en die formules vir vry-vloei toestande is nie geldig nie. Dit was tot nou toe nie
moontlik om vloeitempo ' s akkuraat te bereken onder hierdie nie-modulêre toestande nie.
Hierdie verslag bied 'n opsomming van die bevindinge van 'n navorsingsprojek wat
bogenoemde probleme aangespreek het. 'n Toetsprogram is uitgevoer wat moontlike
konfigurasies van multikepe ingesluit het. Die modelle van die meetstrukture is onder beide
vry-vloei en versuipte toestande bestudeer. Gedurende die ontwikkeling van nuwe formules vir
die berekening van vloeie is daarna gestreef om so veel as moontlik gebruik te maak van
internasionale standaarde. Dit behoort Suid-Afrikaanse praktyke vir andere aanvaarbaar te
maak.
'n Belangrike eienskap van multikepe is die voorkoms van end-kontraksies. Hulle het 'n groot
invloed op vloeimeting en oor die algemeen het 'n keep met groot end-kontraksies 'n laer vloei
koëffisient as 'n vol-wydte keep. End-kontraksies is ook baie effektief om skerpkruine te belug.
Vir vry-vloei toestande is gevind dat 'n metode gebaseer op die IMFT vergelyking (ingesluit in
ISO standaarde) baie goeie resultate lewer. In vergelyking met ander bestaande metodes gee dié
metode die kleinste foute met 'n gemiddelde fout van 0.6%.
Onder versuipte toestande speel end-kontraksies ook 'n belangrike rol, ten minste by beperkte
versuiping. As vol-wydte kepe beskou word, kan gesien word dat die stroom-op watervlak eers
daal voordat dit weer styg (weens ontlugting). Kepe met end-kontraksies ly nie aan hierdie
probleem nie.
Dit is verder bevestig dat versuipte toestande beskryf kan word in terme van 'n energie verlies
wat by die versuipte meetstruktuur voorkom. Hierdie energie verlies is 'n funksie van die
snelhede by die vena contraeta van die keep en by die stroom-af rivier snit. As die verskil
tussen die twee snelhede groot is, is die energie velies ook groot.
Twee bestaande metodes vir versuipte toestande is getoets. Villemonte se vergelyking werk
goed as die energie verliese groot is, terwyl Wessels se metode beter werk as die verliese klein
raak. 'n Prosedure is ontwikkel wat dit moontlik maak om die regte metode te kies vir 'n
spesifieke toestand. Vanaf die toetsdata is bepaal dat die maksimum fout ±10% is by hoë grade
van versuiping (S> 0.80) wanneer bogenoemde prosedure gevolg word.
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