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.

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.

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.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.

Thesis (Ph. D.)--University of Hong Kong, 1998. / Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

The reduction of pile capacity associated with volume contraction of the soil close to the pile surface has been reported in carbonate deposits offshore North West Australia and in residual deposits of Southern Africa. Knowledge of the load carried by the shaft and the pile tip is critical for the determination of the load settlement behavior of piles in structurally unstable and highly variable sand deposits. While the Static and Dynamic formulas and Pile load tests are used for the determination of pile carrying capacity, they are limited in terms of site coverage, cost and adequacy of load settlement data. Since the mode of shearing around a pile shaft is very similar to that observed in the direct shear tests, it is thus cost effective to develop analytical methods based on controlled laboratory model tests in order to predict load settlement behavior and bearing capacity of piles. A simple shear apparatus was developed to investigate whether or not significant contractile strains are induced in low density residual sands subject to simple shear strain and to study the effect of such contractile strain of a soil close to the pile shaft on pile load settlement behavior. The design and development of the simple shear apparatus was based on a new simple shear stress equation. Series of constant normal stresses, constant normal stiffness and constant volume tests were conducted on samples of Berea Sands compacted to low density in the new apparatus, supported by moisture induced collapse settlement and matric suction tests. The tests revealed significant volume contraction of Berea Sands due to imposed simple shear strain. The tests data were fed into a new Winkler - type load transfer model and were used to determine the load - transfer curves of vertically loaded piles. The curves revealed that both the loadsettlement behavior and pile capacity in low density sands are dependent on the volume contraction of the soil in the plastic zone close to the pile surface, horizontal stress normal to the pile shaft and stiffness of the soil outside the plastic zone. / Thesis (Ph.D.)-University of KwaZulu-Natal, 2005.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references (leaves 180-193). Also available in electronic version.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references (leaves 180-185). Also available in electronic version. Access restricted to campus users.

Thesis (M. Sc.)--University of Hong Kong, 2004. / Also available in print.