Doctoral Degrees (Civil Engineering)

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The application of commercial floating car data for speed-based traffic state evaluation in the Sub-Saharan African context
(Stellenbosch : Stellenbosch University, 2023-03) Bruwer, Megan Melissa; Andersen, Simen Johann; Walker, Ian; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: Floating car data (FCD) are traffic data that are passively reported from within the traffic stream by GPSenabled probe devices commonly carried in vehicles, including smartphones, on-board navigation devices, and vehicle tracking systems. Commercial FCD are collected, aggregated, stored, and sold by third-party traffic data entities, providing network-wide speed, travel time, and origin-destination data. Commercial FCD eliminate the need for traffic sensors and communications networks, while simultaneously reducing the data analysis demands typical of Big Data because commercial FCD are characteristically made available in structured and readily usable formats. Commercial FCD are poised to become a primary source of traffic data in low- and middle-income countries where traditional, sensor-based traffic data are only sparsely collected over a vast road network, thereby leapfrogging the extensive traffic data collection systems established in high-income countries. Presently, commercial FCD are not widely used or researched in Sub-Saharan Africa. This dissertation is, therefore, well timed in its aim to assess the correct application of commercial FCD in the Sub-Saharan African context. This dissertation identified that the sample providing commercial FCD results in an inherent bias (called sample bias) because the reporting devices are purchased according to socioeconomic status, particularly in Sub-Saharan Africa, where average income, smartphone penetration and technology uptake is low. This dissertation represents the first time that the term sample bias has been described and systematically investigated as a characteristic of commercial FCD. The research found that commercial FCD are impacted by sample bias according to the socioeconomic, demographic, and geographic distribution of the sample that reports FCD in Sub-Saharan Africa. Sample bias was also proven to impact the accuracy of FCD speeds to the extent that speed accuracy differed between cities in South Africa and between commercial FCD sources. Mathematical models for the correct application of FCD in Sub-Saharan Africa that can be applied irrespective of sample bias, were then considered. Sample bias can be excluded in congestion measurement using ratio indices. FCD were found to enable accurate and comparative congestion measurement, both of recurrent and non-recurrent congestion, using variations of the Speed Reduction Index. Finally, three unique use-case studies, specifically applicable to Sub-Saharan Africa, were carried out to demonstrate the usefulness of FCD to evaluate the impact of roadworks projects, identify potholes along rural routes, and map changes in traffic patterns during the COVID-19 pandemic. The primary contribution of this research will be to steer Sub-Saharan Africa towards applicable use-cases of commercial FCD for transport planning purposes. This dissertation should allow commercial FCD to be applied with confidence for the correct use-cases in Sub-Saharan Africa. This research has provided a guideline for the evaluation of potential sample bias and the impact thereof, demonstrated the huge potential for FCD-based traffic pattern monitoring in a Sub-Saharan African context – for both urban and rural applications – and suggested future research for continued Sub-Saharan-specific FCD application. This research is critical to guide commercial FCD towards a significant role in providing primary traffic data over the extensive road network of our continent.
Aspects of self-cementation when applied in roads
(Stellenbosch : Stellenbosch University, 2019-04) Rudman, Chantal; Jenkins, Kim J.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: Worldwide, the growing volumes of traffic have led to the increase in an expanding infrastructure that must be continually maintained. Congruent with these developments are undesirable environmental consequences, including depletion of natural resources. Given the fact that the construction industry is responsible for more than 40% of extracted materials [Fadiya et al., 2014], and subsequently generates large amounts of construction waste, it is ominous that the roads industry should be a key player in implementing austerity measures. These actions should include progressing to more efficient construction practices and the reuse of materials to alleviate the strain on already overburdened natural resources. Many initiatives and developments have been implemented towards this goal and conventional road construction materials replaced with alternative options such as construction demolition waste – better known as recycled concrete aggregate (RCA) and recycled crushed masonry (RCM). The Netherlands, for example, has been processing RCA and RCM for use in road layers as common practice since the late 1970s and has developed industry norms towards successful utilisation within the construction industry. These applications have been highly satisfactory. It has been reported that mix compositions of RCA and RCM exhibit self‐cementing characteristics. These characteristics could be beneficial to road design. Unfortunately, they are also associated with unforeseen challenges that become more complex when considering mechanisms such as self‐cementation, which manifests over time and potentially influences the performance of such a material. The long‐term performance of this type of self‐cementing, secondary material is not fully understood and long‐term behaviour is often difficult to predict. The change in response of governing mechanisms brought on by self‐cementing could lead to a change in failure behaviour. Potentially, the material could transform between characteristics of an unbound material, governed by rutting and permanent deformation failure, to that of a bound material, in turn governed by fatigue and subsequent cracking behaviour. These could lead to undesired defects, which may appear randomly in terms of severity and therefore require an assessment of the scope of what the long‐term physical, mechanical and durability performance of these materials could entail. Often these changes and associated risks are minimised through decreasing variability of the material when processed in a formalised industry. In emerging markets, characteristic of many developing countries, risk is increased due to informal practices. The current research investigates the range of variability in which the behavioural response of the materials can manifest. It includes the way in which self‐cementing manifests in the micro‐ and macrostructure and the short‐ and long‐term structural performance associated with self‐cementation of RCA. Additionally, the intrinsic and extrinsic factors associated with durability concerns manifesting as a result of the potential transforming nature of RCA, between characteristics of an unbound to a bound layer, are investigated. The research in this regard includes the consequences of carbonation as well as the modelling of test data and its potential for shrinkage crack patterning as a result of fatigue failure behaviour. The results reveal that some benefit can be derived from exploiting the self‐cementing characteristics of the material, but that caution should be exercised in curtailing risk during application of the material within road layers. Finally, guidelines are proposed that account for the factors that may affect the long‐term performance of this material, so that it can be incorporated into normal practice. These considerations include aspects concerning the structural and durability performance of the material (especially in informal markets where standardised processing of materials is not the norm) and the application in construction practices and design considerations.
A beam finite element for the analysis of structures in fire
(Stellenbosch : Stellenbosch University, 2016-12) Walls, Richard Shaun; Viljoen, Celeste; De Clercq, Hennie; Stellenbosch University. Faculty Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: All building structures require a specified fire resistance rating and numerous procedures have been produced for ensuring this. In engineering practice designers can generally not perform detailed structural fire designs on buildings due to the high computational modelling requirements of most modern structures, and so they typically resort to conservative prescriptive methods instead. Hence, design engineer orientated methods are required to improve fire safety while providing more economical buildings. The goal of this dissertation is to provide a simple, but technically accurate, model for the analysis of structures in fire, including composite structures, which considers buildings as skeletal frames. To achieve this end a beam finite element has been developed that has a moving, eccentric neutral axis that accounts for material properties that change as structures heat up. A composite bending stiffness, axial stiffness and resultant thermal forces are calculated for a generic cross-section. Material and geometric nonlinearity is considered. The properties of any number of materials (e.g. a steel beam, concrete slab and reinforcing steel) are represented by single beam properties. These calculated beam properties can be included in either commercially available, but simple, finite element software or advanced finite element modelling tools. The only assumption required is that Euler-Bernoulli behaviour, where plane sections remain plane, must hold. A methodology for including rebar tension stiffening at elevated temperatures has been included based on modifying an ambient temperature model. A series of numerical case studies are presented, comparing the results of the proposed beam formulation against finite element models using shell elements. Results between these models (which includes deflections, stresses, strains and neutral axis positions) typically differ by 0-5% when Euler-Bernoulli assumptions hold. Furthermore, case studies and experimental results from real fire tests in the literature were also analysed by the proposed formulation coupled with relatively simple finite element software. The deflections of structures in fire predicted by the proposed model are well within acceptable tolerances for fire engineering systems, and typically comparable to more complex models in the literature. The model developed has been used to investigate eleven different beams consisting of steel beams, concrete slabs and composite steel-concrete beams, along with conducting a series of parametric studies. With further research and the inclusion of three-dimensional behaviour the method could become a valuable tool for the analysis of structures in fire.
The behaviour of reinforced concrete cantilever columns under lateral impact load
(Stellenbosch : Stellenbosch University, 1989-12) Loedolff, Matthys Johannes; Louw, J. M.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: see item for full text
The calibration of compound crump and sharp-crested gauging weirs in South Africa
(Stellenbosch : Stellenbosch University, 1996-12) Wessels, P. (Pieter); Rooseboom, A.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: The present network of now gauging stations in South Africa has grown from isolated observations on an ad extensive is to an extensive network of stations across the country. Standardised gauging stations to suit local conditions have been developed which include purposely desigll4:d compound weirs. Nearly all. compound gauging weirs In South Africa have. for practical reasons. been constructed without dividing walls. thus deviating lr',:.n the standards set by the British Standards Institution (1981). Uncertainty about the accuracy of calibration of such structures had to be darifi,ed and. where ~cessary. adjustments had to be made to existing calibration formulae in order to compensate for the de,,·iations. It was also necessary to determine whether the accuracies that could be attained were adequate in terms of the potential financial implications of inaccuracies. It has thus become necessary to re-evaluate the calibration of these structures which consist of mainly compound Crump .md sharp-crested weirs. Selected flow l"t'Cords were analysed and the data wa.\ used to determine the impact of errors on the required capacities of reservoirs. This wa., done in an anempt to provide guidelines for the accuracy required in flow records. An31ysing a single application of a flow record cannot provide guidelines for the required accuracy of a flow record and thus the gauging of flow. Although no general conclusions can be drawn. it appears thal the benefits arising from an improvement in the accuracy of a flow record are proportionally greater than the percentage improvement in accuracy. Three-dimensional flow conditions exist either upstream or downstream of the point of stage measurement depending on the presence or absence of diViding walls at a compound gauging weir. The existing calibro1tion theory does not account for the influences of three-dimensional flow conditions and a.-'isociatcd energy losses in the determination of the upstream total energy head. Hydraulic model tests were thus undenaken to detemline the magnitude of the resulting energy losses. New techniques were developed to compensate for these energy losses in the calibration theory of compound gauging weirs. Application of the new calculation techniques to rate compound weirs using a single point of stage measurement results in improvements in accuracy. It was found that compound weirs without dividing walls can be rated to greater levels of accuracy than weirs with dividing walls, where stage measurements are taken at a single point
Characterisation of material properties and behaviour of cold bituminous mixtures for road pavements
(Stellenbosch : Stellenbosch University, 2008-03) Ebels, Lucas-Jan; Jenkins, K. J.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
The cold bituminous mixtures, which are the subject of this study, are obtained by mixing mineral aggregate with either bitumen emulsion or foamed bitumen at ambient temperatures. These techniques are frequently used in Cold In-Place Recycling whereby typically the top 150 – 250 mm of the existing pavement is reworked, as a rehabilitation measure when structural maintenance is required. To differentiate from the cold mixes for surfacing layers the term Bitumen Stabilised Materials (BSM’s) is adopted here. The increased use of BSM’s, shortcomings in the existing design guidelines and manuals and ongoing developments in the concepts and understanding of these materials require further research into the fundamental properties and behaviour of BSM’s. Achieving a better understanding of the fundamental performance properties of BSM’s is the main objective of this study, with a view to using the extended knowledge for improvements to current mix design and structural design practices. The state-of-the-art of bitumen emulsion and foamed bitumen techniques is reviewed in a literature study. Current best practices in the design of BSM’s and pavements incorporating such materials is also included in this literature study. Shortcomings and areas for further improvement of the design practice have been identified. With new environmental legislation that recently came into effect in South Africa, the importance of BSM technology as an environmentally-friendlier and more sustainable construction technique is set to increase in the coming years. A laboratory testing programme was set-up to study the properties and behaviour of BSM’s and to establish links with the compositional factors, i.e. the type of binder used, the percentage of Reclaimed Asphalt Pavement (RAP) in the mix and the addition of a small dosage of cement as active filler. The mineral aggregates used were sourced in the USA and consisted of crushed limestone rock and RAP millings. These were blended in two different proportions of crushed rock : RAP, i.e. 3:1 (with 3.6 % residual binder) and 1:3 (with 2.4 % residual binder). Tri-axial testing (150 mm diamter) was carried out to determine shear parameters, resilient modulus and permanent deformation behaviour, while four-point beam testing was carried out to determine strain-at-break, flexural stiffness and fatigue behaviour. It was found that the process of bitumen stabilisation improves the shear strength of the material, particularly in case 1 % of cement is added as active filler. This increase in shear strength is entirely the result of increased cohesion. There is a good correlation between the shear strength and the resilient modulus of BSM’s. The resilient modulus of BSM is stress-dependent and the Mr-θ model is adequate to model the resilient modulus of the blends with a low percentage of RAP. For the blends with a higher percentage of RAP this model cannot be applied and the resilient modulus reduces in stiffness at higher deviator stress ratios. A considerable part of the efforts of this study were dedicated to characterise and model the permanent deformation behaviour. The General Permanent Deformation Law as originally developed by Francken applies also to BSM’s. An improved nonlinear method to converge at a solution for the model parameters that describe the tertiary flow part of this deformation law was developed as part of this study. Parameters that can be derived from the first stage of the permanent deformation test, i.e. initial strain and initial strain rate as defined in this study, were found that correlate well with the model parameters that describe the first linear part of the deformation law. Critical deviator stress ratios for the several mixes tested were determined. When BSM’s are subjected to loading below these ratios, tertiary flow is unlikely to occur. A high variability was generally found in the four-point beam test results, especially for the strain-at-break. Specimen preparation protocols and the quality of the beam specimens are of utmost importance when performing four-point beam tests on BSM’s. This limits the practical applications of the strain-at-break test. Trends observed in the strain-at-break were also inconsistent and sometimes not in line with the other type of tests. BSM’s exhibit a visco-elastic behaviour, which was determined by flexural stiffness testing, however, to a lesser extent than HMA. Phase angles and Black Diagrams were developed for the BSM’s tested, which also made it possible to determine the parameters of the Burgers Model, which is a mechanical model describing viscoelastic behaviour. Fatigue relationships were also developed for the BSM’s tested. The fatigue performance of these mixes is lower than for selected HMA mixes. The foamed BSM generally showed better fatigue life than emulsion BSM, however, the lower initial stiffness of the foamed BSM’s may contribute to a perceived longer fatigue life. For the mixes tested, the flexural stiffness of foamed BSM’s is generally also lower than that of emulsion BSM’s It is recommended that the mix design of BSM’s be split into two phases. During the first phase the usually large number of variables could be reduced to a selected few by means of UCS and ITS indicator testing. Subsequently, more fundamental parameters should be determined during the second phase, such as shear strength and resilient modulus, as well as permanent deformation behaviour. The fact that commercial laboratories in South Africa do not have tri-axial testing facilities is currently a practical limiting factor. Initiatives currently underway to develop “simple” shear tests are welcomed in this regard. It is proposed that classification of BSM is based on shear strength. There are indications that shear failure in BSM is more critical than failure as a result of fatigue. The effect of curing resulting in an increase in BSM stiffness in the period after construction, i.e. typically 6 to 18 months, is currently ignored in structural design models. The rapid stiffness reduction of BSM’s during the first period after construction in the current structural design models and also found during Accelerated Pavement Testing is not being observed in Long-Term Pavement Performance (LTPP). On the contrary, an increase in stiffness is observed in LTPP. This would indicate that stiffness reduction as a result of fatigue does not occur or is overshadowed by the effect of curing and that fatigue as a failure mechanism of BSM’s is currently over-emphasized.
Characterisation of model uncertainty for reliability-based design of pile foundations
(Stellenbosch : Stellenbosch University, 2007-12) Dithinde, Mahongo; De Wet, M.; Retief, J. V.; Phoon, K. K.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
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.
Characterisation of the South African extreme wind environment relevant to standardisation
(Stellenbosch : Stellenbosch University, 2021-03) Bakker, Frederik Pierre; Viljoen, Celeste; De Koker, Nico; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: To ensure adequate structural resistance, engineers estimate the largest loads that windcan reasonably be expected to induce in a structure. In South Africa, operational designpractices are described in a set of standards, which include a wind loading standard (SANS10160-3) that provides guidance to engineers in estimating wind loads. The estimationprocedure described in the standard uses a basic wind speed, provided in a characteristicmap, that accounts for what the climate could produce at a particular location. This mapis based on inference from available wind speed observations using stochastic models.In an effort to improve the background information on which the standard is basedand in response to greater volumes of wind speed data, this dissertation presents a setof investigations which incorporate a greater quantity of relevant data, strive to improvethe stochastic model, and make specific recommendations that could be included in thenext revision of the South African wind load standard.A background study that summarises some of the most salient theory is also presented.This includes an overview of the South African extreme wind climate, extreme valuetheory, wind load standardisation, and reliability-based design.The quantity of available data collected by the South African Weather Service hasincreased substantially since the current standard was derived. This data had to bechecked for errors and classified by climatic mechanism. Following an attempt to correctfor the dynamic response of outdated instruments, the inclusion of historical data datingas far back as 1948 was also investigated. To be relevant for use in the standard, allthe data had to be measured according to World Meteorological Organisation standards.This was typically not the case, and so surface roughness correction was applied using aGeographical Information System technique. The expanded dataset includes data from an extensive network of 132 stations through-out South Africa, but the use of only annual maxima resulted in insufficient samplesizes at individual sites, potentially introducing substantial model-variance. In response,improved estimates by incorporating data from multiple sites within the region of studywere determined in this thesis. This included regional estimation of the shape of theprobability distribution, based on preconditioning the data by an exponent; and a separateinvestigation on optimal estimation of variability. For estimation of the variability, it wasshown that there was a balance between site and regional estimation, which was used todevelop an optimal estimator based on the bias variance trade-off.The expanded dataset and the insights into regional estimation were then applied toestimate design wind speeds that should satisfy the target reliability specified in the SouthAfrican standard. These estimates were incorporated into a new characteristic wind speedmap using a Monte Carlo simulation-based hypothesis test.
The characterization of the dynamic interaction between highway bridges and long, multi-trailer heavy vehicles
(Stellenbosch : Stellenbosch University, 2022-04) Meyer, Markus Willem; Lenner, Roman; De Koker, Nico; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: Around the world, many countries are experiencing an increase in demand for freight to be transported by road. One solution is to introduce larger heavy vehicles, which are capable of transporting more freight. These vehicles have more trailers, more axles and are longer and heavier than existing heavy vehicle traffic. All these factors have an important influence on the dynamic amplification between the vehicle and bridge. This contribution investigates the dynamic behaviour of long, multi-trailer vehicles, specifically the B-Double vehicles, when crossing short to medium span bridges. The dynamic behaviour of these larger vehicles is compared to the well-known single articulated vehicles which are currently operating in many countries around the world. The effect of axle groups and their spacing on dynamic amplification is explored in depth to support the finding that the time of entry of axle groups on an excited bridge is key to the explanation of dynamic response. The relationship between midspan accelerations and dynamic amplification is introduced and explored extensively for further validation of the findings presented. There is an indication that the commonly accepted inverse relationship between the high static load and observed low dynamic amplification is not generally true when comparing vehicles of different axle configurations. The number of axles, along with inter-axle spacing matching the natural frequency of the bridge, is of substantial relevance to the dynamic response, yielding in some cases higher dynamic amplification of high static loads. It is shown that due to the latter, the significantly heavier vehicles can induce higher dynamic amplification on medium span bridges than some lighter vehicles with different axle configurations. Furthermore, a dynamic load signature is developed which defines the typical dynamic loads induced by B-Double vehicles at midspan for short to medium span bridges. It is shown that the dynamic loads can be defined as a function of the first natural frequency of the bridge and the midspan accelerations. Ultimately, a new method of estimating dynamic amplification factors by implementing a dynamic load signature function in addition to strain and acceleration measurements, is proposed.
Comparative evaluation of the model-centred and the application-centred design approach in civil engineering software
(Stellenbosch : Stellenbosch University, 2002-12) Sinske, A. N. (Alexander Nicholas); Dunaiski, P. E.; Mult, H. C.; Pahl, P. J.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: In this dissertation the traditional model-centred (MC)design approach for the development of software in the civil engineering field is compared to a newly developed application-centred (AC)design approach. In the MC design software models play the central role. A software model maps part of the world, for example its visualization or analysis onto the memory space of the computer. Characteristic of the MC design is that the identifiers of objects are unique and persistent only within the name scope of a model, and that classes which define the objects are components of the model. In the AC design all objects of the engineering task are collected in an application. The identifiers of the objects are unique and persistent within the name scope of the application and classes are no longer components of a model, but components of the software platform. This means that an object can be a part of several models. It is investigated whether the demands on the information and communication in modern civil engineering processes can be satisfied using the MC design approach. The investigation is based on the evaluation of existing software for the analysis and design of a sewer reticulation system of realistic dimensions and complexity. Structural, quantitative, as well as engineering complexity criteria are used to evaluate the design. For the evaluation of the quantitative criteria, in addition to the actual Duration of Execution, a User Interaction Count, the Persistent Data Size, and a Basic Instruction Count based on a source code complexity analysis, are introduced. The analysis of the MCdesign shows that the solution of an engineering task requires several models. The interaction between the models proves to be complicated and inflexible due to the limitation of object identifier scope: The engineer is restricted to the concepts of the software developer, who must provide static bridges between models in the form of data files or software transformers. The concept of the ACdesign approach is then presented and implemented in a new software application written in Java. This application is also extended for the distributed computing scenario. Newbasic classes are defined to manage the static and dynamic behaviour of objects, and to ensure the consistent and persistent state of objects in the application. The same structural and quantitative analyses are performed using the same test data sets as for the MCapplication. It is shown that the AC design approach is superior to the MC design approach with respect to structural, quantitative and engineering complexity .criteria. With respect to the design structure the limitation of object identifier scope, and thus the requirement for bridges between models, falls away, which is in particular of value for the distributed computing scenario. Although the new object management routines introduce an overhead in the duration of execution for the AC design compared to a hypothetical MC design with only one model and no software bridges, the advantages of the design structure outweigh this potential disadvantage.
Computational and Experimental Modelling of Masonry Walling towards Performance-Based Standardisation of Alternative Masonry Units for Low-Income Housing
(Stellenbosch : Stellenbosch University, 2019-12) De Villiers, Wibke Irmtraut; Van Zijl, G. P. A. G.; Boshoff, William Peter; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: South Africa has a housing shortage estimated in excess of 2 million units. This backlog is being addressed predominantly with the construction of 40m2 low-cost, single storey, detached state subsidised houses built with conventional masonry units (CMU’s), namely concrete and burnt clay. The use of these materials has a significant negative impact on the environment and the thermal performance of conventional masonry walls is generally poor. These factors, and others, have led to the development of alternative masonry units (AMU’s) in South Africa, and internationally, with a lesser environmental impact and improved thermal performance. However, lack of standards presents a significant barrier to the uptake of AMU’s The regulatory framework governing the use of masonry in South Africa, and possible avenues through which AMU’s could gain access to the market, are explored. It is found that AMU’s could provide a reasonable and socially acceptable alternative to CMU’s in low-income housing (LIH) but the current regulatory framework does not accommodate AMU’s in a sufficiently practical manner to enable their widespread, off-the-shelf uptake. The ongoing process of the adoption of Eurocode 6 and the accompanying materials and testing standards by the South African masonry industry, facilitates the transition from prescriptive to performance-based (PB) regulation of masonry design. It is proposed that material non-specific, PB requirements for masonry units for structural application in LIH can be developed to assist the inclusion of AMU’s in the open market. To quantify PB criteria, two critical configurations of single-storey bonded masonry walls are generated, based on the deemed-to-satisfy provisions of the National Building Regulations (NBR). Subsequently, a simplified micro-scale finite element (FE) model is used to analyse these configurations under serviceability and ultimate limit state loading conditions, to serve as a performance prediction model from which PB criteria can be derived. Four masonry materials are selected for the study; conventional concrete (CON), alkali-activated material or geopolymer (GEO), compressed-stabilised earth (CSE) and adobe (ADB), representing a wide spectrum in terms of strength and stiffness. Characterisation tests of the four materials are used, together with numerical fitting to test data and data taken from literature, to generate the necessary parametric input for the FE model. The results of medium to large-scale in-plane and out-of-plane tests are used for validation of the FE model. The FE analyses revealed that for most of the load cases, the resistances of the walls failed to achieve the design load, even for the conventional CON blocks. A significant shortfall was found for the out-of-plane resistance against the wind load for all four materials, as well as structural vulnerability under seismic loading due to the geometric layout permitted by the deemed-to-satisfy rules in the NBR. These results preclude the immediate derivation of PB criteria for AMU’s but contribute significantly to the body of knowledge surrounding FE modelling of AMU’s. They also indicate that the NBR provisions for wall panel geometry require reconsideration, given the recent revision of the South African loading code. However, material non-specific PB regulation is still the recommended avenue for the standardised inclusion of AMU’s.
A computerised decision support system for the implementation of strategic logistics management optimisation principles in the planning and operation of integrated urban public transport
(Stellenbosch : Stellenbosch University, 2001-12) Duff-Riddell, W. R. (Wayne Russell); Bester, C. J.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: Public and private transport system planning and operation have tended to be fragmented functions. In particular, public transport is often planned and operated independently of the "private" transport system. South African government policy now requires that comprehensive, strategic transport plans be prepared by metropolitan transport authorities. These plans are expected to conform to national strategic objectives as well as including local current and longterm objectives. This planning is required in the environment of a multi-modal, multi-operator, public-private partnership scenario that is new for most of the role players. The lack of experience is accompanied by a lack of any existing model for dealing with this scenario. This dissertation describes such a model. The model is based on the principles of strategic logistics management commonly employed in commerce and industry, including service-oriented industries. The modelling process is thus based on achieving a combination of customer service and long-term objectives. The model comprises a number of separate components and steps: • A transport network model (Emme/2). ~ A multi-class, generalised-cost assignment of private and public transport demand onto a network, modified to be modeless to the public transport users, is performed. This assignment allows for the imposition of generalised-cost reflecting urban-planning objectives in addition to more conventional costs such as travel cost. In this assignment, the interaction of public and private transport is accounted for and results in an associated modal choice. ~ A series of single-class generalised-cost assignments is then used to "focus" public transport demand to create corridors of demand adequate to justify public transport routes. This process can be enhanced to develop a design promoting switching from private to public transport. It also allows for multi-period route design. ~ The results of this modelling process are output to a text file and then subject to the processes described below. The results of these processes are then input into the network model where a standard transit assignment is performed and used to modify the proposed lines and update the network design data with respect to boardings and alightings at nodes. This information is used to design fixed infrastructure. • A Microsoft Access database and route extraction program. );> The network model data is drawn into the database where it is subject to a route extraction program that converts the assignment results from the network model into a set of mode specific potential public transport route definitions. These route definitions are based on paths of maximum demand. The extraction process is controlled by parameters specified by the planner, such as minimum route lengths and the demand level for various categories of service. );> After route extraction, vehicle allocation, and transit assignment, the database provides details of the boardings and alightings and number and details of transit lines using each node and link in the network. This data is used to design fixed infrastructure. • A Microsoft Excel spreadsheet vehicle operating cost model. );> For each vehicle type, the operating cost given the anticipated vehicle mileage and operating speed is determined. This is used to guide the choice of vehicles for different routes. • A Lingo goal-programming model. );> The potential routes and the available or potential fleet are subjected to a goalprogramme in which the optimum choice of vehicle allocation is determined. The allocation parameters can be controlled by the planner. These parameters may include costs, energy, fuel consumption, and vehicle and route limitations amongst others. Multiperiod design is included in the modelling process so that the optimum design may be for the operating period, daily, or weekly cycle. The modelling process provides two main outputs: • A set of fully described and costed transit lines ill terms of both routing and vehicle allocation. These transit line definitions can be output to the level of driver instructions if necessary. • Details of the type and location of infrastructure to be provided on the network.
A contribution to the advancement of geotechnical engineering in South Africa
(Stellenbosch : Stellenbosch University, 2013-03) Day, Peter William; Retief, J. V.; Van Zijl, G. P. A. G.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
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.
Contributions to structural mechanics and durability in structural engineering
(Stellenbosch : Stellenbosch University., 2016-12) Van Zijl, Gideon Pieter Adriaan Greeff; Boshoff, William Peter; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: Contributions to structural engineering have been made since 2001 from the basis of the Department of Civil Engineering of Stellenbosch University (SU). The inauguration of the Centre for Development of Sustained Infrastructure (CDSI) in 2002 has been instrumental in defining, directing and scoping the research and development in the categories Advanced cement-based construction materials, Crack formation and durability towards durability design, Renovation and retrofitting towards extended life span and Sustainable energy harvesting structures. The contributions are structured along these categories as chapters of this dissertation. Early career background in structural Engineering at the Institute for Structural Engineering (1987-1989) and Bureau for Mechanical Engineering (1989-1992) and higher education in computational and structural mechanics (PhD 1995-1999, Research Fellow 1999-2001, TU Delft), shaped the research interests in these fields. Continued affiliation with TU Delft (30%) and SU (70%) in the years 2001-2009 provided access to collegial expertise in related fields of experimental research, materials engineering, risk and reliability, and structural design at these institutions and beyond. In this way, national and international collaboration complemented structural and computational mechanics in well-rounded research programs in the mentioned categories. Clearly, the contributions are the result of collaboration in which the author to various degrees led, participated in and supervised research and development. Highlights of the contributions in the four categories are described at a relatively high level towards conveying the contributions in the national and international context. To a degree selective reporting is done, and the reader directed to detailed elaborations in roughly 200 dissertations, theses and technical papers supervised or co-supervised, authored and co-authored. Approach by the infrastructure pre-fabrication industry in South Africa towards development of accelerated and new product lines led to the development of advanced cement-based construction materials (ACM) with local ingredients, and appropriate adaption of the materials to industrial fabrication process of high-pressure extrusion. What started as fibre inclusion towards reduced traditional steel reinforcement in concrete pipes, led to development, characterisation, manufacturing and constitutive modelling of steel fibre concrete and strainhardening cement-based composites (SHCC). Roles of international leadership in co-chairing and chairing RILEM technical committees followed, as well as co-editing of books on the state-of-the-art of Durability of SHCC and a Framework of durability design with SHCC respectively. Particular contributions of significant potential towards the ability to design for durable, sustainable infrastructure, were made in chloride-induced corrosion and alkali silica reaction. In both cases crack formation and durability, i.e. structural durability in service conditions are the points of departure in order to assess actual structural performance in presence of such deteriorating processes. The work in ACM was extended to ultra-high strength concrete, and recently to lightweight aerated concrete (LWAC) and lightweight foam concrete (LWFC). The thermal, acoustic and potential mechanical advantages of LWAC and LWFC are subjects of a current significant research effort in the CDSI towards developing these lightweight materials for structural application in residential infrastructure. Constitutive models developed for traditional construction materials, as well as several of the ACM, enabled the iterative computationalexperimental development and validation of retrofitting strategies for both unreinforced load-bearing masonry and reinforced concrete structures for new functionality or extended structural life span. Finally, a role of leadership and collaboration was fulfilled in research of the solar chimney power plant concept with national and international partners, bringing the concept for harvesting of sustainable energy to a pre-feasibility level. The contributions have laid the link between construction material properties, structural behaviour and durability. Through the fundamental experimental research, structural mechanics and computational mechanics, it has been made possible to utilise the advanced properties of ACM to advance structural performance and durability. Human capital well-versed in the fundamental principles of this multi-level structural engineering approach has been developed in the process of research supervision by the author.
Contributions to the implementation of the principles of reliability to the standardized basis of structural design
(Stellenbosch : Stellenbosch University, 2015-12) Retief, Johannes Verster; Van Zijl, Gideon P. A. G.; Viljoen, Celeste; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: Implementation of the principles of structural reliability widely impacted on recent improvements in structural performance. Improvements in the rational basis for the design of structures in turn have a bearing on the ability of structural engineers to contribute to the safety, functionality and economy of structures to accommodate the activities and infrastructure serving society. This dissertation presents a number of investigations that can broadly be classified to explore and advance the implementation of reliability concepts and procedures in standardized structural design. The context of the investigations is provided by various activities on the development of revised or new South African standards for structural design, utilising international standards as reference base. The principles of reliability provide the common basis for the harmonization of national and international standards, unification between various standards which are common to specific structures and reliability assessment for classes of design variables and performance functions. Specific investigations considered the general basis of structural design required for a suite of standards; the reliability modelling of actions and their combinations, including wind loading, imposed roof loads and crane induced loads; structural resistance, including structural concrete shear and cracking performance, the reliability performance of pile foundations. Generalisation of the detailed investigations consists of the identification of the attributes of structural design standards that could serve as the basis for meta-standard drivers for standards development and their management. A common theme in many investigations is the consideration of model uncertainty and the need for its proper quantification for use in reliability assessment. Accordingly generalisation consists of the compilation of a classification scheme for classes of model uncertainty and systematic procedures for the investigation and implementation of model uncertainty. The scheme can also be used to provide a basis for planning of research activities on which model development can be based. The investigations confirm the potential for value to be added at the interface between reliability theory and design practice, despite the maturity of the field. Examples presented in the dissertation include detailed investigations on design variables such as South African strong wind characteristics and wind load reliability models, extensive investigations on concrete shear resistance models and their uncertainties, and pile foundation reliability calibration. General investigations on the reliability basis of design contributed to demonstrate the achievement of harmonisation between the new South African Loading Code SANS 10160:2010 and Eurocode to the extent that the South African standard serves as an example of the application of Eurocode beyond Europe. A common basis also serves to unify national standards for the design of various structural materials ranging from steel to geotechnical materials, having widely diverse origins ranging from adoption to local development. Finally the investigations reveal both remaining topics begging further investigation and a methodology for prioritisation and integrating the outcomes into the general reliability framework.
Coupled fully three-dimensional hydro-morphodynamic modelling of bridge pier scour in an alluvial bed
(Stellenbosch : Stellenbosch University, 2019-12) Vonkeman, Jeanine Karen; Basson, G. R.; Smit, G. J. F.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: Local scour at piers has been cited as the main mechanism responsible for the collapse of bridges founded in alluvial beds and yet there is no universally agreed upon design procedure to accurately predict the equilibrium scour depth. The scour process was investigated by a 1:15 scale physical model for a combination of different flows, pier shapes and sediment beds, from which the scour patterns and flow velocities were measured. The experimental data was used to evaluate thirty empirical equations for bridge pier scour, which were found to produce a wide range of unreliable results. No single equation is conclusively superior but the HEC-18 equation is proposed, as well as equations that rely on the pier Reynolds number, a parameter which has been shown to be significant in the horseshoe vortex formation. Subsequently, an improved dimensionless shape factor and armouring factor based on the particle Reynolds number were developed for the HEC-18 equation from field data measurements. Although extensive research has been published on bridge pier scour for more than six decades, comparatively few studies have been presented on the detailed 3D numerical modelling of such processes. The key aim of this study was to develop an improved coupled fully three-dimensional hydro-morphodynamic model with the Immersed Boundary method and Reynolds Stress Model to simulate pier scour. The proposed numerical model computes bed shear stresses from implicit wall functions and adopts an Eulerian multi-fluid model to account for rolling and saltating particles. Numerical instabilities were addressed in the sediment transport submodels which were ascribed to the fine mesh resolution required to resolve the crucial horseshoe vortex and the diffusion resulting from the discretization of the Immersed Boundary method. The Reynolds Stress Model was compared with the 𝑘𝑘-ε turbulence model but it was found that the results from the numerical model are more sensitive to the computational grid than to the choice of turbulence model to resolve the horseshoe vortex and to obtain stability. Despite the perceived limitations of the proposed hydro-morphodynamic model, the model demonstrated that the velocity flow field, the horseshoe vortex and the subsequent maximum bridge pier scour upstream of the pier nose can be modelled successfully to simulate the results from the experimental work. The simplicity of conservative empirical equations may be feasible for the conceptual design of bridges. However, advanced numerical models have the ability to better account for the interaction of several interrelated parameters and the intricate vortex systems responsible for the scour process at bridge piers. It is proposed that the primary subject of future studies for bridge pier scour should be on the comparison of numerical models with one another.
Coupled fully three-dimensional mathematical modelling of sediment deposition and erosion in reservoirs
(Stellenbosch : Stellenbosch University, 2015-03) Sawadogo, Ousmane; Basson, G. R.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: The investigation of reservoir sedimentation has become an important and valuable research topic in engineering practice. Sediment deposition in reservoirs can affect ood levels, drainage for agriculture land, pumpstation and hydropower operation and navigation. An extensive review of the technical literature pertaining to suspended sediment transports as well as deposited sediment ushing from reservoirs has shown that most studies on sediment are still based on empirical formulas and experimental work, despite the availability of sophisticated computers. This is because sediment transport and particularly sediment deposition and erosion are complex processes, that involve the interaction of many physical factors which are not easily modelled numerically. In addition, most of the existing three-dimensional numerical models are not coupled hydrodynamic and sediment transport models. They first simulate the velocity field and water depth and then the concentration and bed change are calculated. Furthermore, they are not fully three-dimensional models for using layer-averaged approaches in conjunction with Saint-Venant equations. The key objective of the present research was to develop a coupled fully three-dimensional (3D) numerical model based on Navier-Stokes equations which includes both the sediment transport component and hydrodynamic parameters. In this regard, a physical model was set up in a laboratory ume in order to investigate the bottom outlet sediment ushing under pressure in a controlled environment. The proposed coupled fully 3D numerical model was used to simulate the experimental tests. Results from these simulations were in good agreement with the measurements. The geometric features of the scour hole (temporal and spatial hole development) upstream of the bottom outlet were reasonably well predicted compared to the experimental data. Furthermore, the velocity field upstream of the bottom outlet was in good agreement with measurements. The proposed numerical model can be considered reliable provided that the model is correctly set up to reflect the condition of a particular case study. Finally, the coupled fully 3D numerical model for turbulent suspended sediment transport in reservoirs was validated against a range of typical reservoir sediment transport and deposition laboratory flume cases. The proposed suspended sediment transport model successfully predicted both sediment deposition and entrainment processes and therefore, it can be used for turbulent suspended sediment transport assessments in reservoirs.
Cracking of Plastic Concrete in Slab-Like Elements
(Stellenbosch : Stellenbosch University, 2016-03) Combrinck, Riaan; Boshoff, William Peter; Stellenbosch University. Faculty of Engineering. Dept of Civil Engineering.
ENGLISH ABSTRACT: The cracking of plastic concrete involves two cracking types namely: plastic settlement cracking which is caused by differential settlement of the concrete and plastic shrinkage cracking which is caused by evaporation of free concrete pore water. These cracks are mainly a problem for slab-like elements exposed to conditions with high evaporation rates and typically occur within the first few hours after the concrete has been cast. The early occurrence of these cracks greatly reduces the durability and service life of a concrete structure. These cracks remain a problem in the construction industry even though there are several effective, but mostly neglected, precautionary measures. The reasons these cracks remain a problem are due to the complex nature of the cracking as well as the lack of a unified theory or model that can account for all the complexities involved. With this in mind, this study aims to fundamentally understand both plastic settlement and plastic shrinkage cracking in slab-like elements individually and combined as well as to determine the tensile material properties of plastic concrete. Once the cracking is fundamentally understood the final objective is to develop a model that can simulate the cracking of plastic concrete using a finite element method approach. The fundamental understanding of these cracks was obtained by conducting various tests on different mixes at various climates and in various moulds. The tests showed that both crack types can occur separately, where plastic settlement cracking occurs first in the form of multiple cracks at the surface as well as shear induced cracks beneath the surface, followed by plastic shrinkage cracking in the form of a singular, well defined crack. In addition, a significant deviation from the individual cracking behaviour was observed when combining these cracks, highlighting the shortfall of most available literature where these cracks are seldom researched in tandem. From all the tests, six different cracking behaviours were identified depending on the potential severity for each cracking type. The test also showed worryingly that both these cracks can be present internally without being visible at the concrete surface where they act as weak spots for future crack growth. The practically challenging tensile testing of plastic concrete was conducted with a newly built direct tensile test setup, which provided stress-strain curves that were used to determine the tensile material properties of plastic concrete such as: Young’s modulus, tensile strength, strain capacity and fracture energy. This included tests at different temperatures as well as cyclic tests. The results showed that the tensile material properties develop significantly faster, the greater the ambient temperature surrounding the concrete as well as the resilient nature of a still plastic concrete which proved to be capable of withstanding cyclic loading without failure, while a solid but still weak concrete could not. The tensile material properties together with the measured strains of plastic concrete were combined to provide both an analytical and numerical estimation of the cracking behaviour of plastic concrete. The analytical estimation was more simplistic and required a few crude assumptions, while the numerical estimation used finite element methods to create a model that accounted for the major complexities involved such as time-dependency of material properties and anisotropic volume change of plastic concrete. Both the analytical and finite element model gives adequate representation of the cracking behaviour for extreme climates but not for normal climates, with the size discrepancy between the interior and surface cracks during experiments as well as the relaxation of stresses in plastic concrete being provided as the main reasons for the poor correlation. The finite element model was further used to conduct a parameter study, where the settlement and shrinkage strains were shown to govern the size of the final crack, while the material properties only influence the time of crack onset and rate of crack widening. Finally, the finite element model was successfully applied to a large scale example of a concrete slab, indicating that the model can be a helpful tool to simulate the cracking of plastic concrete without the need to perform timely experiments.
Delay and disruption claims and damages in relation to construction projects
(Stellenbosch : Stellenbosch University, 2016-03) Malan, Antonie du Toit; Strasheim, J. A. v B.; Lubbe, G. F.; University of Stellenbosch. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: The project management triangle, also referred to as the “triple constraint” or the “iron triangle”1 is a model of the constraints of project management. The triangle is used to illustrate that the success of project management is measured by the project team’s ability to manage the project so that the expected results are produced while managing time and cost. Events or circumstances may occur during construction contracts which may delay or disrupt the execution of the works or cause loss of productivity. All modern standard-form contracts provide for extending the date for completion under certain defined circumstances, but few contracts, if any, adequately address the question of on what basis exactly the extension of time is to be determined. This uncertainty and inconsistency creates numerous problems for the contractors in planning their work prospectively, and consequent delays may result in severe financial penalties, loss and expenses. This uncertainty and inconsistency may even have the completely opposite effect of relieving the contractor of his obligation to pay penalties and leaving the employer with the unexpected consequence of being obliged to prove its damages. Where the contract does not make express provision for an eventuality or the allocation of risk, the circumstance will be governed by common law. In other words, if the contract is silent on some of above common issues, the parties will be obliged to revert to common law for the outcome of their dispute. The main source of common law in relation to construction law is case law, of which there is a relative dearth in South Africa on the many issues that arise from the interpretation of contractual provisions dealing with delay and disruption in construction projects. It is therefore important for contracts to provide expressly for risk allocation pertaining to possible delaying events and to determine the distinction between time risk and cost risk events. Delay and disruption matters, which may inter alia include issues involving extensions of time, penalties, critical path, ownership of float, concurrent delay, delay analysis methods, global claims, and time at large, among other factors, all too often become disputes that have to be decided by third parties, including inter alia mediators, adjudicators, dispute review boards, arbitrators, and judges. The number of such cases could be substantially reduced by the introduction of an unambiguous and consistent approach. This thesis will address the above concepts by analysing the applicable legal principles involved. This will be done through an analysis of case law and legal writings, and a comparison of different standard contracts from South Africa, England, and, to a lesser extent, other foreign jurisdictions. This analysis will be applied and compared to the newly published JBCC suite of contracts (Edition 6.1 March 2014). Provisions of the JBCC extension of time regimen that are inconsistent and conflicting and may create ambiguity will be identified, and the thesis will propose amendments. Furthermore, provisions which are susceptible to time-at-large arguments will be analysed and appropriate amendments will be proposed. Finally, the thesis will endeavour to introduce Best Practice Project and Risk Management principles through its proposed amendments.
Derivation of a traffic load model for the structural design of highway bridges in South Africa
(Stellenbosch : Stellenbosch University, 2020-03) Van der Spuy, Pierre Francois; Lenner, Roman; O'Brien, Eugene; Casas, Joan Ramon; Retief, Johan; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: This study sets out to derive a new traffic load model for the design of highway bridges in South Africa, with novel contributions to the field of bridge traffic loading. The current code for bridge design in South Africa, Technical Methods for Highways 7 (TMH7), was published in 1981 and was shown by previous studies, and by this study, to be deficient at characteristic level. This is especially true for shorter spans. TMH7 does not give any indication of the levels of safety used to calibrate the code and it is therefore not clear whether the code is still providing the necessary safety margins. Several studies, outlined in this document, show that the Uniformly Distributed Load (UDL) and knife edge loads for type NA loading should be increased. NA is referred to in TMH7 as normal loading. Further to this, the legal limit for Gross Vehicle Weight (GVW) was increased to 56 t and the vehicle characteristics on our roads have changed significantly since 1981. TMH7 loading is widely regarded in industry as too complex to apply and engineers have called for a simplified load model. A study of this nature is therefore well motivated to ensure safety of road users and to increase design efficiency for bridge engineers. Derivation of traffic load models requires measured traffic data. Previous studies showed that at least one year of Weigh in Motion (WIM) data is required to make accurate predictions of load effects at long return periods. Most WIM sensors in South Africa are located on National Route 3 (N3) and National Route 4 (N4) which are the major import and export routes in the country and which also carry the heaviest traffic. Stations along these routes are considered to be well calibrated. A WIM station along the N3 at Roosboom is chosen for this study, as seven years of traffic from 2010 to 2016 are available and the station is considered one of the heaviest loaded in the country. A comparison with other stations confirms this. In contrast with TMH7, it is typical in international codes to provide a load model for the slow, or heavy, lane which is reduced transversely by Multiple Lane Factors (MLFs). To align with international norms, a slow lane model is derived in this study based on the seven years of data at the Roosboom station as discussed previously. This measurement record includes the identification of 12.5 million heavy vehicles. The slow lane in the direction from Durban to Johannesburg is studied as vehicles in this direction are heavier than vehicles travelling from Johannesburg to Durban. Span lengths that are investigated range from 5 m to 50 m in increments of 5 m. The model derived herein is not valid for span lengths outside these bounds. The load effects (LEs) that are investigated are hogging on two span structures and sagging and shear on single span structures. For characteristic loads a 5 % probability of exceedance in a 50 year reference period is selected, similar to the Eurocode and the South African building design codes. This leads to a characteristic return period of 975 years. A censored GEV distribution is introduced to model the LEs. The shape factor is almost always negative, indicating an underlying Weibull distribution. This confirms the finding of other researchers that traffic LEs are bounded. The characteristic axle load amounts to 160 kN, which is used to calculate a UDL to replicate the characteristic load effects, resulting in a slow lane load model with a UDL of 13 kPa and a triple axle of 160 kN, spaced at 1.2 m. To distribute the slow lane model transversely, it is necessary to derive MLFs which take into account the reduced probability of simultaneous heavy vehicles in adjacent lanes. A novel method is presented in this work in which multiple lane WIM data is used to calculate MLF factors. A WIM station in Pretoria at Kilner Park measures four lanes of traffic at 0.01 s accuracy. This is the only station in South Africa measuring more than two lanes. By studying concurrent characteristic LEs in adjacent lanes it is possible to determine MLFs, first for two lanes loaded, then three lanes loaded and finally for four lanes loaded. The resulting MLFs are 1.0; 0.78; 0.07; 0.00. This implies that traffic from the fourth lane does not contribute to the characteristic global LEs. Vehicles that travel at speed, referred to as free flowing traffic, cause additional forces on bridge decks due to dynamic interaction between the vehicles and a bridge (Vehicle Bridge Interaction - VBI). To account for these increased loads, it is typical to multiply the static loads by a dynamic amplification factor (DAF) which is defined as the ratio between the total load effect to the static load effect. It is not the aim of this study to do an in depth investigation of dynamic amplification for South African bridges and it is therefore decided to adopt the values given in the ARCHES report D10, which are based on European traffic. It is reasonable to assume that South African roads conform to at least class B road profiles, implying a DAF of 1.4 up to 5 m span length and reducing linearly tot 1.2 at a 15 m span length. Seeing that South African vehicles are heavier than in Europe and have more axles, it is reasonable to assume that the DAF for South African traffic would be lower than for Europe. The ARCHES values can therefore be considered to be conservative in the absence of a comprehensive VBI study and measurements. To derive a design load model, it is necessary to establish Partial Factors (PFs) in accordance with structural reliability theory. Target 50 year β values are taken in accordance with the South African building design codes, which are based on extensive studies of historical practise in South Africa. For Ultimate Limit State (ULS), the 50 year β value is taken as 3.5 for a high consequence of failure and for Serviceability Limit State (SLS) as 1.5. The SLS value is in accordance with international standards. The reliability index is directly related to the probability of failure and hence it is possible to determine return periods of 435 years for SLS and 5040 years for ULS. For traffic loads, where the return periods for static loads are long, the probabilities of non-exceedance are close to 1.0 for characteristic, SLS and ULS. This leads to very small differences in load effects between characteristic and ULS return periods, especially when a censored GEV distribution is fitted which tends towards the Weibull distribution. When the LEs are near the bound of the fitted underlying Weibull distributions then there is hardly any uncertainty in the loading and all the uncertainty is located in the resistance. A new approach is introduced to address statistical uncertainty in fitting parameters. As seven years of data is used it is not surprising to find very small statistical uncertainty. Final partial factors are a function of reliability based partial factors, model uncertainty and statistical uncertainty. These amount to 1.18 for SLS and 1.33 for ULS. Chapter 8 presents a worked example for a typical bridge configuration for various widths and span lengths and considers both characteristic loads and ULS. The findings from this section are that the new model with DAF is always critical for all deck widths, for all span lengths and load effects when compared to normal loading in TMH7. The new model also exceeds LM1 in the Eurocode at characteristic and ULS levels. Although TMH7 abnormal and super loading is compared to the new model, it should be compared to a separate new model for abnormal loading which is outside the scope of this study.

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