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- Volume 55, Issue 2, 2013
Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese - Volume 55, Issue 2, 2013
Volumes & issues
Volume 55, Issue 2, 2013
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 55, pp 2 –7 (2013)More Less
The objective of the paper is to provide an understanding of the South African concrete industry's environmental burden in terms of natural resource consumption and carbon dioxide equivalent emissions (CO2-e). The review covers current practices in the concrete construction field in South Africa (SA) and their implications for the environment. Elaboration in terms of detail and quantification is given for the environmental burden generated during the manufacture of raw materials for concrete and their transportation to site. Four-year average (2005-2008) data is provided for resources consumed and wastes emitted during the quarrying and manufacture of raw materials for concrete. Carbon dioxide-equivalent emissions data per unit of material produced was obtained from the InEnergy Report produced for the Cement and Concrete Institute (C&CI) of South Africa. The study determined that, on average, 39.7 Mt of raw materials are consumed per year and 4.92 x 109 kg CO2-e emissions are emitted per year to produce cement and aggregates for concrete production in South Africa.
Relationship between creep time dependent index and Paris Law parameters for bituminous mixtures : technical paperAuthor M. Mostafa HassanSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 55, pp 8 –11 (2013)More Less
Bituminous mixtures undergo cracking, either top-down or bottom-up, as a consequence of the repeated application of traffic loads, thermal cycling or a combination of the two mechanisms. Cracking is considered as one of the major distress modes in asphalt pavements.
This study presents a method to characterise crack resistance of asphaltic mixtures containing waste materials using a semi-circular bending (SCB) fracture test. Three different bituminous mixtures containing incinerator bottom ash waste and one control mix, containing limestone, were tested under cycling SCB loading conditions at 5°C and the results were interpreted using Paris Law. The same mixtures were also tested under controlled stress creep conditions at the same temperature. This paper examines the link between the time dependent index from creep tests with the n parameter from the Paris Law model, based on visco-elastic continuum damage mechanics analysis and linear elastic fracture mechanics principles.
A procedure for critical path method-based scheduling in linear construction projects : technical paperAuthor O. OkmenSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 55, pp 12 –20 (2013)More Less
Construction projects having identical or similar units, in which activities repeat from one unit to another, require schedules that ensure the continuous usage of resources from one unit to the next and the maintenance of the network logic between activities at the same time. This paper presents a procedure for critical path method-based (CPM) scheduling in linear construction projects that have repeating activities. The procedure concurrently provides the utilisation of resources without interruption and preservation of network relationships between successive units. With this procedure it is possible to represent activities by variable production rates through consecutive units and assign any kind of relationship type with lag time. The proposed procedure determines the critical units in two categories: logical and resource critical units. A spreadsheet has been developed on a table processor to computerise the procedure. Details of the procedure are described and an example application is presented.
Management concepts and project performance : perceptions from the South African public sector environment : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 55, pp 21 –28 (2013)More Less
The thrust of this paper is to examine management strategies that could engender performance improvement in construction. Using the South African infrastructure sector as the geographical limit of the study, the research reported upon emanates from a quantitative study that was underpinned by the review of related literature. A survey was conducted among general contractor (GC) members of the South African Federation of Civil Engineering Contractors (SAFCEC), consulting engineer members of Consulting Engineers South Africa (CESA) and selected public sector clients.
Based on inferential statistics, selected findings show that inconsistent and inadequate risk allocation and management practices could lead to inappropriate choice of procurement strategy. Inadequate documentation and transfer of experience and performance could also result in limited organisational knowledge, learning and transfer. The lack of delivery management skills within public sector establishments could result in poor execution of projects, and an inappropriate organisational culture among project partners may lead to resistance to the changes that are necessary for inculcating performance improvement.
Although these aforementioned perceptions pertain to a limited number of respondents, especially the individuals working for the clients in the public sector, their views are insightful. As most of the participants were generally involved in public sector construction projects, their opinions can point to a way forward.
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 55, pp 29 –45 (2013)More Less
The accurate estimation of strong winds is of cardinal importance to the built environment, particularly in South Africa, where wind loading represents the dominant environmental action to be considered in the design of structures. While the Gumbel method remains the most popular applied method to estimate strong wind quantiles, several factors should influence the consideration of alternative approaches. In South Africa, the most important factors influencing the choice of method are the mixed strong wind climate and the lengths of available wind measurement records. In addition, the time-scale of the estimations (in this case one hour and 2-3 seconds) influences the suitability of some methods.
The strong wind climate is dominated by synoptic scale disturbances along the coast and adjacent interior, and mesoscale systems, i.e. thunderstorms, in the biggest part of the interior. However, in a large part of South Africa more than one mechanism plays a significant role in the development of strong winds. For these regions the application of a mixed-climate approach is recommended as more appropriate than the Gumbel method.
In South Africa, reliable wind records are in most cases shorter than 20 years, which makes the application of a method developed for short time series advisable. In addition it is also recommended that the shape parameter be set to zero, which translates to the Gumbel method when only annual maxima are employed. In the case of the Peak-Over-Threshold (POT) method, one of several methods developed for short time series, the application of the Exponential Distribution instead of the Generalised Pareto Distribution is recommended. However, the POT method is not suitable for estimations over longer time scales, e.g. one hour averaging, due to the high volumes of dependent strong wind values in the data sets to be utilised. The results of an updated assessment, or the present strong wind records reported in this paper, serve as input to revised strong wind maps, as presented in the accompanying paper (see page 46).
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 55, pp 46 –58 (2013)More Less
Although wind is the most important environmental action on buildings and structures in South Africa, the last comprehensive strong wind analysis was conducted in 1985. The current wind loading code is still based on the strong wind quantiles forthcoming from that analysis. Wind data available for strong wind analysis has increased about five-fold, due to the employment of automatic weather station (AWS) technology by the South African Weather Service. This makes an updated assessment of strong winds in South Africa imperative.
Based on the estimation of strong winds as reported in the accompanying paper (see page 29 in this volume), the spatial interpolation of 50-year characteristic strong wind values to provide updated design wind speed maps is reported in this paper. In addition to taking account of short recording periods and the effects of the mixed strong wind climate, the exposure of the weather stations was considered and correction factors applied. Quantile values were adjusted to compensate for the small data samples. The resultant design maps reveal regions of relatively high and low quantiles, but with an improved relationship with physical conditions compared to the previous analyses.
Consequently some significant differences in quantiles between the present and previous analyses were found. The complexity of the resulting strong wind maps is not only the result of the improved resolution of the larger number of weather stations, but also due to an improved identification of the effects of physical factors such as the mixed strong wind climate and topography. Guidance can also be derived for future updating, such as incorporating accumulated observations and improved coverage by additional AWS in critical regions.
Experimental study of turbulence and water levels in shoaling and breaking waves using digital image processing techniques : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 55, pp 59 –74 (2013)More Less
In this article we present results of laboratory experiments undertaken to study the structure of turbulence generated by mild plunging waves breaking on a sloping beach bed. Measurements of water levels and instantaneous fluid velocities were conducted on a 1:20 sloping beach fitted inside a glass flume. The instantaneous water levels were measured using calibrated capacitive wave gauges, while the instantaneous velocity flow fields were measured using video techniques together with digital correlation techniques. A digital camera was employed to capture images of the breaking waves at 20 phases. For each phase, 100 image pairs were captured from which 100 instantaneous velocity fields were derived using a digital correlation image velocimetry technique. The 100 instantaneous velocity flow fields were averaged to provide information on the mean flow. Further analysis of the acquired data yielded turbulence quantities such as turbulence intensity, turbulent kinetic energy and vorticity at each phase of the flow. Results are presented for four phases where turbulence is predominant. Contour plots are used to provide a temporal and spatial distribution of the evolution of the turbulence characteristics. Vertical profiles of these quantities at different phases are also presented. These results may provide guidance on the approximations that can be expected in computational fluid model studies.