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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Sediment transport dynamics in South African estuaries

Beck, 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.
22

Risiko-gebaseerde besluitondersteuning in siviele ingenieurswese: 'n metodologiese benadering tot verbeterende inligtingversameling en benutting

Bester, 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.
23

Characterisation of model uncertainty for reliability-based design of pile foundations

Dithinde, 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.
24

A contribution to the advancement of geotechnical engineering in South Africa

Day, 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.
25

Mechanical and structural characterisation of extrusion moulded SHCC

Visser, 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.
26

Best practice of crane support structures design : an expert survey

Thompson, 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.
27

An experimental investigation into the behaviour of a 5 ton electric overhead travelling crane and its supporting structure

De 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.
28

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 studies

Dzvukamanja, 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.
29

Reliability of reinforced concrete shear resistance

Huber, 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.
30

The rating of compound sharp-crested weirs under modular and non-modular flow conditions

Canto, 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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