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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.
1

An investigation of overhead crane wheel/rail/girder interaction

Perez Winkler, A. R. 03 1900 (has links)
Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The aim of this thesis is to investigate the wheel/rail/girder interaction of overhead cranes. Three components of the above mentioned interaction system are considered. • The contact interaction between the crane wheel and the rail and its effects on the rail stresses. • The stress distribution in thin webbed rails and the location of critical stresses in the rail. • The load distribution between the rail foot and the crane girder with the inclusion of elastomeric pads. The steps followed for the purpose of this investigation were: • The creation of a numerical wheel-rail interaction model with the finite element method. • The experimental and analytical verification of the numerical results. • An analysis of the wheel/rail/girder interaction system variables on the basis of the numerical results. The following conclusions were drawn from the investigation: • The variables with the greatest influence on the wheel-rail contact patch shape, size and critical stress are the crane wheel diameter and the railhead curvature radius. • It is the position of the above mentioned contact patch relative to the rail symmetry plane, rather than the wheel-rail contact patch size, shape and critical stress, that has a significant influence on the rail stress distribution as a whole. • Critical stresses in thin webbed rails are found at the web-foot and web-head junctions. • The load distribution between the rail foot and the girder, in case elastomeric pads are included, can be described using the beam on elastic foundation theory. / AFRIKAANSE OPSOMMING: Die doél van hierdie tesis is om die interaksie tussen die wiel, die spoor en die ondersteunende balk van oorhoofse krane te ondersoek. Die klem val op die interaksie van drie komponente van bogenoemde sisteem nl:. • Die kontak: interaksie tussen die kraanwiel en die spoor en die gevolglik effekte op die spanningsverdeling in die spoor. • Die spanningsverdeling in kraanspore met dunwandige webbe en die lokasie van kritieke spannings. • Die spanningsverdeling tussen die onderste spoorflens en die bo-flens van die ondersteunende balk in die geval dat 'n elastomeriese strook tussen bogenoemde flense ingesluit word. Die stappe vir die ondersoek was as volg: • Die skepping van 'n numeriese wiel-spoor interaksie model met die eindige element metode. • Die eksperimentele en analitiese verifikasie van numeriese resultate. • Die analise van die wiel/spoor/ondersteunende balk sisteem veranderlikes gebaseer op numeriese resultate. Die belangrikste resultate van die ondersoek was dat: • Die veranderlikes met die grootste invloed op die grote, vorm en kritieke spannings van die wiel-spoor kontak area is die kraan wiel radius en die radius van die spoor se bo-vlak kromming. Dit is die posisie van bogenoemde kontak area relatieftot die simmetrievlak van die spoor, in plaas van die wiel-spoor kontak area grote, vorm ofkritieke spanning, wat 'n deurslaggewende invloed op die spanningsverdeling in die kraanspoor het. • Kritieke spannings in spore met dunwandige webbe word aan die bokant en onderkant van die spoor web aangetref. • Die spanningsverdeling tussen die onderste spoor flens en die bo flens van die ondersteunende balk kan, in die geval dat 'n elastomeriese strook tussen bogenoemde flense ingesluit word, met die gebruik van balk op elastiese fondament teorie beskryf word.
2

The development of a multi-purpose beam/column testing apparatus

Koen, Colin Boyd 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: A multi-purpose beam/column apparatus is developed to ensure successful testing of structural elements and to optimise the main test floor of the Structures Laboratory of the University of Stellenbosch. An overview of the testing of structural elements is given as background to beam and column testing, with specific reference to the test sample, the test arrangement and the test data. The test arrangement, with reference to the test setup boundary conditions (static and kinematic), and the loading are discussed. A summary of the collection and the processing of the test data is given and frequently used and standard test setup is described. The requirements and the various components of the testing apparatus are discussed and a three-dimensional CAD model of the apparatus is developed to illustrate the versatility of the apparatus. A rational planning process is developed to optimise the testing and pre-test planning process with specific reference to the use of the apparatus. This rational planning process is defined as the process of preparing, testing and evaluating structural tests and together with the literature review will ensure meaningful test results. The use of the apparatus, built by the Department of Civil Engineering, University of Stellenbosch and the use of the rational planning process are illustrated by testing the deflection of a welded truss, from which conclusions are drawn. / AFRIKAANSE OPSOMMING: 'n Veelsydige balkkolom apparaat is ontwikkel om die gebruik van die hoof-toetsvloer van die Struktuur Laboratorium van die Universiteit van Stellenbosch te optimiseer en suksesvolle struktuurtoetse te verseker. As agtergrond tot die ontwikkeling van die MTA word 'n oorsig gegee oor balk-en-kolom toetse, met spesifieke verwysings tot die toetsstuk, die toets-opstelling en die toets-data. Die toets-opstelling word bespreek met spesifieke verwysing na die grenstoestande (staties en kinematies) en die aangewende belasting. Die versameling en die verwerking van toetsdata en die algemeen gebruikte en standaard toets-opstellings word bespreek. Die vereistes van die verskillende komponente van die apparaat word bespreek en 'n driedimensionele CAD model van die apparaat word gebruik om die veelsydigheid van die apparaat te beklemtoon. 'n Rasionele beplanningsproses, wat spesifiek verwys na die gebruik van die apparaat, word ontwikkel. Hierdie beplanningsproses wat die beplanning, uitvoer en evaluasie van strukturele toetse insluit, saam met die literatuur agtergrond, verseker sinvolle toetsresultate. 'n Gesweisde vakwerk word getoets om die gebruik van die apparaat, gebou deur die Departement van Siviele Ingenieurswese, Universiteit van Stellenbosch en die gebruik van die rasionele beplanningsproses te illustreer. Gevolgtrekkings word gemaak na aanleiding van hierdie toetse.
3

Investigation into the top flange and web deformation in a crane girder panel

Viljoen, P. de K. 12 1900 (has links)
Thesis (MEng) -- Stellenbosch University, 2004. / ENGLISH ABSTRACT: The purpose of this project was to study the deformations of the top flange and web of a girder panel resulting from loads, which have been imposed by an overhead travelling crane. This was achieved by designing a crane girder that represents dimensional ratios occurring in practice. The first part of this project attempts to determine the properties of the crane girder. The crane girder was built from drawings in the workshop of the University of Stellenbosch’s Civil-Department. Positions were identified where the strains were to be measured on the crane girder. The crane girder was subjected to loads according to SABS 0160 - 1989 and measurements were taken. The same beam was also modelled with finite elements. The numerical model was subjected to the same loads as the experimental crane girder. Comparisons were then made between the results of the experimental investigation and those of the numerical model. Good comparisons were achieved between the results and the numerical model was assumed to be correct. Other students could now use this model for investigating local stresses and strain effects that might cause fatigue and other in-service problems of electric overhead travelling cranes support structures in practice. / AFRIKAANSE OPSOMMING: Die doel van hierdie projek was om die vervormings van die boonste flense en web van ’n kraanbalkpaneel te ondersoek, as gevolg van laste wat onderworpe was aan ’n oorhoofse kraanbalk. Dit was bereik deur ‘n balk te ontwerp wat dimensionele verhoudings in die praktyk verteenwoordig. In die eerste gedeelte van die projek word die eienskappe van die kraanbalk bepaal. Die kraanbalk was vanaf tekeninge in die werkswinkel van die Universiteit van Stellenbosch se Siviele Departement gebou. Posisies was geidentifiseer waar die vervormings op die kraanbalk gemeet sou word. Die kraanbalk was onderwerp aan laste volgens SABS 0160 - 1989 en meetings was geneem. Dieselfde balk was ook gemodelleer met eindige elemente. Die numeriese model was aan dieselfde laste as die eksperimentele balk onderwerp. Vergelykings was toe verkry tussen the resultate van die eksperimentele ondersoek en die numeriese model. Goeie vergelykings tussen die resultate was behaal en die numeriese model word as korrek aanvaar. Ander studente kan nou hierdie model gebruik vir die ondersoek na lokale spannings en vervormingseffekte wat moontlik vermoeidheid en ander in-diens probleme van elastiese oorhoofse kraan ondersteunende strukture in the praktyk kan veroorsaak.
4

Object-oriented finite element framework

Olivier, Albertus Hendrik 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: The role of the computer has changed from a calculation tool to a tool that supports human thinking. In this thesis fundamental aspects of the Finite Element method are mapped to an object model with a well defined structure which provides for local and distributed analysis work. To achieve this the following was investigated: • An object-oriented framework for the Finite Element analysis method • An associated graphical user interface that enables the user to create and modify Finite Element models in an effective way • Requirements for the sharing of analysis information in a communication network Proposed solutions are implemented in a pilot application which indicates their potential. / AFRIKAANSE OPSOMMING: Die rol van die rekenaar het verander vanaf 'n gereedskapstuk wat berekening doen na 'n gereedskapstuk wat menslike denke ondersteun. In hierdie tesis word die fundamentele aspekte van die Eindige Element metode oorgedra na 'n objek model met 'n goed gedefinieerde struktuur wat lokale en verspreide analisering werk ondersteun. Om dit te bereik is die volgende ondesoek: • 'n Objek orienteerde raamwerk vir die Eindige Element metode • 'n Geassosieerde grafiese raamwerk wat die gebruiker in staat stelom objekte te skep en te verander • Vereistes vir die deel van analise inligting in 'n kommunikasie netwerk Die voorgestelde oplossing is geimplimenteer in 'n loodsimplementering wat die voordele van die benadering uitlig.
5

Factors influencing asphalt compactibility and its relation to asphalt rutting performance

Douries, William John 04 1900 (has links)
Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This thesis covers the factors affecting compactibility of hot mix asphalt including gradation, filler/binder ratios, binder types, binder content, polymer modification, temperature, volumetric properties etc. The study is not limited to compactibility as the property measured, but also on the influence of these factors on the mix’s capacity to resist permanent deformation or rutting. An experimental design was used with a variety of the above factors being included. Laboratory analysis of the mixes as well as accelerated pavement testing of different mix types using the one-third scale Model Mobile Load Simulator (MMLS3) was carried out. The analysis assists in identification of the factors that influence both compactibility and rut resistance, those influencing the one but not the other, and those factors having no significant influence. The compactibility of the mixes has been analysed in terms of voids in the mix at a specific binder content and compaction level. Special consideration was given to the characterisation of the filler and filler/binder system of some mixes. It was found that gradation of a mix has a significant influence on compaction and the rutting performance. High filler/binder ratios were found to be the critical factors influencing the compactibility of the wearing course mixes investigated, but based on the limited tests performed, the reduction of the filler/binder ratios for improved compactibility did not significantly increase rutting under accelerated pavement testing. As expected, the binder type has a significant influence on the rutting resistance as well as compactibility. In addition, an increase in binder content facilitated compaction, but decreased rutting resistance. Polymer modification considerably improved the rutting resistance of a standard mix under the same loading conditions. Although some modifiers may improve rutting resistance, it requires higher compaction temperatures. The addition of the antistripping agent Gripper L decreased the rutting, aggregate stripping and also the rate of rutting of the Quartzite LAMBS mix that result from the stripping failuremechanism. Low densities can lead to considerable rutting and moisture damage, especially when a moisture susceptible aggregate is used. In terms of compactibility as evaluated with the Superpave Gyratory Compactor, it appears that there exists a temperature window in which compaction can be achieved, but in terms of rutting; even a small deviation in temperature can influence rutting results significantly. The control of the temperature during testing is critical if meaningful comparisons between different mixes with regard to rutting performance are to be made. Linear elastic and finite element analysis has been performed to ascertain whether different specimen geometries would influence the stress distribution within the specimen, and subsequently the rutting results. It was found that the geometry of test specimens has an influence on the stress distribution within the specimens, which can influence the permanent deformation results. The briquette specimens tested in the laboratory also yielded higher rutting results for the same mix tested in the field. It is therefore important to use specimens that are most representative of field conditions / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die faktore wat ’n invloed het op die kompakteerbaarheid van warm asfalt. Faktore sluit in onder andere gradering, vulstof/bindstof verhouding, tipe bindstof, bindstof inhoud, polimeer modifisering, temperatuuur, volumetriese eienskappe, ens. Hierdie studie is nie net beperk tot kompakteerbaarheid as ‘n gemete eienskap nie, maar ook die invloed van hierdie faktore op die mengsel se vermoë om weerstand te bied teen permanente deformasie of spoorvorming. ’n Eksperimentele ontwerp wat ’n verskeidenheid van bogenoemde faktore insluit is gebruik. Laboratorium analise van die mengsels asook versnelde plaveisel toetse van die verskillende tipe mengsels is gedoen met die een-derde skaal Mobiele Lassimuleerder (MMLS3). Die analise help met die identifikasie van die faktore wat beide kompakteerbaarheid en spoorvorming beïnvloed, asook dié wat slegs die een maar nie die ander beïnvloed, en ook die faktore wat geen beduidende invloed het nie. Die kompakteerbaarheid is geëvalueer in terme van die hol ruimtes in die mengsel by ’n bepaalde bindstof inhoud en verdigtingsgraad. Spesiale aandag is geskenk aan die eienskappe van die vulstof en vulstof/bindstof wisselwerking van die mengsels. Die gradering van ’n mengsel het ’n beduidende invloed op kompakteerbaarheid sowel as spoorvorming. Hoë vulstof/bindstof verhoudings is een van die kritiese faktore wat die kompakteerbaarheid van die betrokke mengsels beïnvloed, maar laer vulstof/bindstof verhoudings vir beter kompaksie het nie ’n beduidende toename in wielsporing teweeg gebring nie. Soos verwag het die tipe bindstof ’n beduidende invloed op kompakteerbaarheid sowel as spoorvorming. ’n Toename in bindstof bevorder verdigting, maar lei tot groter wielsporing. Polimeer modifisering verminder die wielsporing van ’n standard mengsel onder dieselfde beladingstoestand. Alhoewel modifisering wielsporing verminder, vereis dit hoër kompaksie temperature.Die toevoeging van die teenstropingsmiddel GripperL verminder spoorvorming, aggregaat stroping asook die tempo van spoorvorming van die Kwartsiet LAMBS mengsel as gevolg van die stropingsmeganisme. Lae digthede kan lei tot aansienlike vogskade en spoorvorming; veral as die aggregaat vatbaar is vir die invloed van vog. Daar blyk ’n temperatuur interval te wees waarin verdigting met die Superpave Gyratory Compactor bereik kan word; maar selfs ‘n klein temperatuurafwyking kan beduidende invloed op die resultate van spoorvorming hê. Temperatuurbeheer is baie belangrik indien sinvolle vergelykings tussen die sporingsgedrag van verskillende mengsels gemaak moet word. Lineêr elasties en eindige element analise is uitgevoer om te bepaal of verskillende toetskonfigurasies die spanningsverdeling binne die toetsmonsters en die spoorvorming affekteer. Dit is bevind dat die geometrie van toetsmonsters het ’n invloed op die spanningsverdeling in die monsters wat die sporingsresultate kan beïnvloed. Die briketmonsters in die laboratorium gee ook groter spoordiepte teenoor dieselfde mengsel wat in die veld getoets is. Daarom is dit belangrik om verteenwoordigende monsters te gebruik.
6

Numerical (FEA) evaluation of crane end buffer impact forces

Haas, Trevor Neville 12 1900 (has links)
Thesis (PhD (Civil Engineering))--University of Stellenbosch, 2007. / The current codes of practice for the design of structures which were studied during this investigation do not explicitly account for the flexibilities and interactions of the Electric Overhead Travelling Crane (EOHTC) and the crane support structure. This leads to analysing the EOHTC and the gantry structure as a decoupled system for ease of computation. Thus, the interaction of the various components of the EOHTC and gantry structure is ignored, which may result in an incorrect assessment of the forces computed in the gantry structure’s members. This led to a study to determine the effects of a EOHTC on the gantry structure. The research was conducted through a series of limited experimental tests and extensive advanced Finite Element Analysis (FEA) simulations. This resulted in developing a computationally efficient FEA model of the full scale experimental EOHTC testing facility in the structural engineering laboratory at Stellenbosch University. The FEA model was developed to conduct simulations for the various load models, namely, vertical wheel load, horizontal longitudinal load and the horizontal lateral load models, as prescribed by the various codes. The research was then focussed at determining the maximum end buffer impact force responses when the crane runs into the end stops. The other load models were investigated by another researcher using the same FEA model. The results from the experimental tests were used to calibrate the FEA simulations. This proved exceptionally challenging due to the various structural response phenomena which occur during the impact of the crane against the end stops. A good correlation between the experimental values and the values predicted by the FEA simulations was achieved for the first impact. Modal analysis and modal superposition methods of analysis were used to determine the effect of the modes of vibration on the structural response to the end buffer impact. A FEA sensitivity analysis was conducted on a set of identified parameters which have a significant effect on the structural response to the end buffer impact. The maximum end buffer impact force was determined for a chosen level of reliability based on the responses from the sensitivity analysis using the Lagrange Multiplier method. These maximum end buffer impact forces are then compared with the forces prescribed by the codes. SABS 0160 slightly underestimates, while SANS 10160 severely overestimates the end buffer impact force obtained from the constraint optimization technique for a target level of reliability of β =3.
7

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.
8

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.
9

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.
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Reliability modelling of performance functions containing correlated basic variables, with application to construction project risk management

Ker-Fox, Gregory Mark 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Correlation mechanisms describing systematic variations and common sensitivities are critical contributors to uncertainty in quantitative functions modelling project performance in terms of probabilistic or basic variables. Current reliability methods transform dependent vectors to an equivalent set of independent standard normal variates. A simple method is developed for dealing with correlation in the original variable space. An algebraic description of the direction cosine (or alpha) for performance functions under conditions of dependence is formally derived and numerically validated. The resultant General First Order Second Moment (GFOSM) method for correlated basic variables is shown to be equivalent to the orthogonal transformation method. Geometric and physical interpretations of the general direction cosine are developed, with alpha found to be equivalent to the correlation between a basic variable and performance function. Corresponding inequalities and normalizing conditions are also developed for alpha. Expressions for a number of applications utilising the general dependent form for the direction cosine are derived and demonstrated. The current definition of the direction cosine as an importance factor is validated for dependent conditions, and conditions established under which this descriptor is no longer adequate. Expressions are derived to measure the significance of a variable in terms of stochastic importance and function sensitivity, to establish reliability index sensitivity to the omission of non-critical items, quantifying variable elasticity and an elasticity index. The general FOSM method for correlated basic variables is applied to system analysis to generate modal correlation coefficients between failure modes. The general direction cosine is stable for multivariate linear functions and functions of limited curvature across a range of reliabilities and correlation levels. This characteristic further simplifies the process by providing for deterministic reliability modelling of performance functions containing dependent variables, avoiding the solution of the more complex joint density function. The extension of the current theory and the treatment of performance functions in the original vector space develop invaluable insight into the correlation mechanisms driving risk and reliability. This will assist project managers to better understand areas that can affect project performance, to focus management attention, develop mitigation strategies and to allocate resources for the optimal management of project risk. / AFRIKAANSE OPSOMMING: Korrelasie meganismes wat sistematiese afwykings en gemeenskaplike sensitiwiteite veroorsaak, is kritieke bydraers tot onsekerheid in kwantitatiewe funksies wat projek prestasie modelleer m terme van probabilistiese of basiese veranderlikes. Huidige betroubaarheidsmetodes transformeer afhanklike vektore tot 'n ekwivalente stel van standaard normaalonafhanklike veranderlikes. '0 Eenvoudige metode is ontwikkelom die effekte van korrelasie in die oorspronklike vektorspasie te hanteer. 'n Algebraise beskrywing van die rigtingseosines (genoem alfa) vir prestasiefunksies onder omstandighede van afhanklikheid is formeel afgelei en numeries gevalideer. Dit is bewys dat die resulterende Algemene Eerste Orde Tweede Moment metode vir gekorreleerde basiese veranderlikes ekwivalent is aan die tradisionele Ortogonale Transformasie metode. Geometriese en fisiese interpretasies vir die algemene rigtingscosinus is ontwikkel, met bewys dat alfa ekwivalent is aan die korrelasie tussen 'n basiese veranderlike en die prestasiefunksie. Ooreenstemmende ongelykhede en normaliserings-kondisies is ook vir alfa ontwikkel. Uitdrukkings vir 'n aantal toepassings wat gebruik maak van die algemene afhanklike vorm van die rigtingscosinus is afgelei en gedemonstreer. Die huidige definisie van die rigtingscosinus as 'n belangrikheidsfaktor is gevalideer vir kondisies van afhanklikheid en omstandighede is uitgewys wanneer dit onvoldoende is. Uitdrukkings is afgelei om stochastiese belangrikheid te meet asook funksie sensitiwiteit, die sensitiwiteit van die betroubaarheidsindeks tot die weglating van nie kritiese veranderlikes, sowel as die kwantifisering van elastisiteit en die elastisiteitsindeks. Die Algemene Eerste Orde Tweede Moment metode vir gekorreleerde' veranderlikes is toegepas op sisteem analise om die korrelasie tussen falingsmodes te genereer. Die algemene rigtingscosinus is stabiel vir liniêre funksies en funksies met 'n beperkte kromming oor 'n reeks betroubaarheidswaardes en korrelasie vlakke. Hierdie kenmerk vereenvoudig die metode verder deur voorsiening te maak vir deterministiese betroubaarheidsmodellering van prestasie funksies met afhanklike veranderlikes, deur die oplossing van die meer komplekse gesamentlike-digtheidsfunksies te vermy. Die uitbreiding van die huidige teorie en die hantering van prestasie funksies in die oorspronklike vektor spasie ontwikkel waardevolle insig in die korrelasie meganismes wat risiko en betroubaarheid oorheers. Hierdie insig sal projekbestuurders in staat stelom kritieke gebiede wat projek prestasie kan affekteer beter te verstaan, om hulle aandag daarop te fokus, om teenmaatreël-strategieë te ontwikkel en hulpbronne toe te ken vir die optimale bestuur van projek risiko.

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