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- Volume 54, Issue 2, 2012
Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese - Volume 54, Issue 2, 2012
Volumes & issues
Volume 54, Issue 2, 2012
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 54, pp 2 –14 (2012)More Less
Design flood estimations display relatively wide confidence bands of uncertainty around all estimates of flood magnitude-frequency relationships. Taking cognisance of this, and the fact that most of the available design flood estimation methods in South Africa were developed in the 1970s and have not been updated since, led to the development of the Standard Design Flood (SDF) method (Alexander 2002a; 2002b; 2003). In this study, the SDF method was evaluated by establishing the accuracy of the regionalised SDF runoff coefficients, taking both the areal extent and homogeneous hydrological catchment responses into consideration. The SDF runoff coefficients were evaluated, calibrated and verified at a quaternary catchment level in SDF basin 9 (primary study area) and in 19 of the other 29 SDF basins in South Africa (secondary study areas) by establishing catchment parameters and evaluating the ratios between the results obtained through the SDF method and probabilistic analysis. The results showed that the original SDF method overestimated the magnitude and frequency (return period) of flood peaks in all the basins under consideration, while the verification results confirmed that the calibrated/verified SDF method, based on quaternary runoff coefficients, significantly improves the accuracy in comparison with the probabilistic analysis results. The result confirmed that the probabilistic-based approach of the original SDF method does not have the ability to overcome the deficiencies evident in the other design flood estimation techniques used in South Africa. Revision of the runoff coefficients at a quaternary catchment level is proposed.
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 54, pp 15 –26 (2012)More Less
The use of Geographical Information Systems (GIS) has permeated almost every field in the engineering, natural and social sciences, offering accurate, efficient, reproducible methods for collecting, viewing and analysing spatial data. GIS do not inherently have all the hydrological simulation capabilities that complex hydrological models do, but are used to determine many of the catchment parameters that hydrological models or design flood estimation methods require. The purpose of this study was to perform catchment parameter analysis using GIS applications available in the ArcGIS environment. The paper will focus on the deployment of special GIS spatial modelling tools versus conventional manual methods used in conjunction with standard GIS tools to estimate typical catchment parameters, e.g. area, average catchment and watercourse slopes, main watercourse lengths and the catchment centroid. The manual catchment parameter estimation methods with GIS-based input parameters demonstrated an acceptable degree of association with the special GIS spatial modelling tools, but proved to be sensitive to biased user-input at different scale resolutions. GIS applications in an ArcGIS environment for the purpose of catchment parameter analyses are recommended to be used as the standard procedure in any proposed hydrological assessment.
What are the legal remedies available to contractors and consultants to enforce payment ? : technical paperAuthor M.J. MaritzSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 54, pp 27 –35 (2012)More Less
Smooth cash flow ensures the effective delivery of projects and is fundamental to develop and sustain a healthy, professional and competitive construction industry. The adverse effect of late or non-payment of contractors and consultants are well known to all in the construction industry. Late and non-payment problems have forced countries like the United Kingdom (UK), Singapore, New Zealand and Australia to introduce legislation to regulate the payment of contractors and consultants in terms of a building or a construction contract. From South African specific surveys conducted by the Construction Industry Development Board (CIDB) and Consulting Engineers South Africa (CESA) it appears that local building and construction contractors and consultants have the same problems as their international counterparts (if not more so) when it comes to payment of work completed or services rendered. In light of the above this article investigates the legal remedies available to enforce right of payment for work completed or services performed, to determine the effectiveness of the said remedies, and to suggest what possible solutions there are in order to improve payment practices in the South African building and construction industry.
Author T.F.P. HenningSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 54, pp 36 –44 (2012)More Less
This paper details findings from the New Zealand Transport Agency's research project by Henning and Roux (2008). It forms part of the overall New Zealand Long-term Pavement Performance (LTPP) programme. The paper documents the development of prediction models for dense-graded asphalt (AC) surfaces and open-graded porous asphalt (OGPA) surfaces. Two models were developed including crack initiation on AC surfaces and ravelling initiation on OGPA surfaces. Continuous probabilistic models were utilised for both crack and ravelling initiation in order to predict the probability of the defect occurring. Models developed during this research use data which is readily available on network level databases, and can therefore be applied to asset management applications such as the New Zealand (NZ) dTIMS system (NZ's nationally adopted pavement management system (PMS)). Although a crack initiation modelwas also developed, it was not as robust as the ravelling model. Further work required includes refining of the models based on the LTPP data which includes bitumen property data. Although the developments are solely based on NZ data, there are a number of aspects applicable to the South African context. Firstly it presents a novel way of modelling the performance of asphaltic surfaces. Secondly it demonstrates some practical implications of maintenance practices that are sometimes considered for South African conditions.
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 54, pp 45 –54 (2012)More Less
The east coast of South Africa has been the subject of numerous coastal developments over recent years. The design of such developments requires a thorough analysis of the local wave climate. Richards Bay and Durban's Waverider data are two relatively long east coast data sets (18 years). These data sets have not been formally reviewed since Rossouw (1984) analysed existing wave data for South African and Namibian coastal waters. This paper aims to provide a formal analysis of the KwaZulu-Natal wave data.
Seasonal exceedance probability plots, wave roses and typical wave parameter statistics are presented. Return periods for extreme waves are estimated from the generalised extreme value distribution, and the associated limitations are discussed.
The average peak period on the east coast of South Africa is 10.0 seconds, the average significant wave height is 1.65 m and the average wave direction is 130 degrees. Autumn has the most frequent and the largest wave events while summer is the only season unlikely to produce either large or frequent events. The recurrence interval of the largest recorded significant wave height (8.5 m) was estimated to be between 32 and 61 year.
Coastal defences on the KwaZulu-Natal coast of South Africa : a review with particular reference to geotextiles : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 54, pp 55 –64 (2012)More Less
Modern coastal defences have to satisfy economic, environmental and sustainability criteria. The balancing of these criteria can make the implementation of coastal defences socially, environmentally and politically complicated. Durban's local authority, the eThekwini Municipality, has had experience with numerous forms of coastal defences in its attempts to balance the operations of a port and associated beach erosion problems. In March 2007 the KwaZulu-Natal coastline suffered severe damage from an extreme storm event which necessitated the installation of additional coastal defences. This paper evaluates Durban's experiences of coastal defences, and details the successes and failures to provide practical insight to those faced with similar circumstances or considering the implementation of coastal defences.
Adjudication as an alternative dispute resolution method in the South African construction industry : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 54, pp 65 –70 (2012)More Less
Adjudication has recently been introduced to the South African construction industry as an alternative dispute resolution mechanism. This study investigates what the requirements are for the industry to realize the full potential of adjudication. To this end the study reviews the necessary contractual, institutional and legislative framework, discusses relevant skills and available training, and establishes what impact all these have on the current practice of adjudication.
A literature review was conducted, covering the local and international practice of adjudication. A structured interview was conducted with adjudicators, and those who were out of geographic reach were sent a survey questionnaire. The results obtained were statistically analysed.
Adjudication appears to have found acceptance in the South African construction industry, but it was found that the industry is not yet able to realize the full potential of adjudication, the main reason for this being a lack of knowledge.
Influence of mica on unconfined compressive strength of a cement-treated weathered granite gravel : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 54, pp 71 –77 (2012)More Less
The road construction industry faces a shortage of naturally occurring gravel materials that meet the requirements for base or even at times sub-base quality. This situation is exacerbated in some cases by the occurrence of mica in soils. This is reported to significantly affect the engineering properties of materials, including plasticity index and compacted density. The objective of this paper is to investigate the influence of mica on the unconfined compressive strength (UCS) and volumetric changes of a cement-treated gravel material. Free mica (muscovite) was added in predetermined percentages by mass to neat gravel (G5) and specimens subjected to a series of standard laboratory tests. The results show that UCS of greater than 3 MPa is achievable by stabilising less than 5% mica content gravel material with at least 4% cement. Mica content beyond 10% results in very low UCS, even for cement content greater than 6%.
A step towards standardising accelerated corrosion tests on laboratory reinforced concrete specimens : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 54, pp 78 –85 (2012)More Less
Natural steel corrosion of reinforced concrete (RC) structures is a slow process which researchers find necessary to accelerate in laboratory tests to obtain needed damage in a short time. Regrettably, there is no standard procedure for accelerating steel corrosion in RC specimens. Researchers therefore continue to use various techniques to accelerate it. Unfortunately, structural damage and rate of steel corrosion are dependent on the accelerated corrosion technique used. Despite that, results obtained by researchers are applied by structural engineers and asset managers to in-service structures. This paper reviews previous techniques used to accelerate steel corrosion. Where possible it proposes standard procedures to accelerate steel corrosion. In other instances it points out needed further research. One of the procedures recommended in the paper is to contaminate selected faces of RC specimens with chlorides, as opposed to immersing samples in NaCl solution or adding chlorides to concrete mixes. It is also recommended to allow specimens to sufficiently dry during steel corrosion so as to promote steel corrosion.
The effects of placement conditions on the quality of concrete in large-diameter bored piles : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 54, pp 86 –93 (2012)More Less
In South Africa, concrete in large-diameter bored piles is generally placed by discharging a highflow concrete mix directly from the truck mixer and allowing the concrete to fall freely to the base of the pile hole. While certain site practices have been used by piling contractors for years,many engineers are not convinced of their acceptability.
In order to assess the effects of free-fall concrete placement, a series of tests were undertaken in which the properties of concrete placed in this manner were compared with the properties of conventionally placed concrete. The tests included an assessment of the effect of water and spoil in the pile hole at the time of casting, as well as poor placement techniques.
The results of this investigation indicate that casting of concrete in 50 mm and 400 mm of water in the bottom of the pile hole significantly reduced the compressive strength by approximately 50% and 80%, respectively. Furthermore, the effect of spoil at the bottom of the pile hole was dependent on the amount of water present.
Finally, a separate investigation, at a bridge site, indicated the free-fall placement technique to be at least as effective as the tremie technique.
The discontinuity required at an air valve or vent for effective pipeline de-aeration : technical paperAuthor S.J. Van VuurenSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 54, pp 94 –100 (2012)More Less
The location and sizing of air valves to ensure effective de-aeration of pipelines and to provide vacuum break capability was researched. Based on these findings, software was developed to evaluate gravity and pumping systems.
A sound understanding of the factors affecting the hydraulic transportation of air in a pipeline is paramount for locating air valves. When air is hydraulically transported to the position of release from the pipeline, it is necessary that the free air should be intercepted by a discontinuity and expelled via an air valve or vent arrangement.
Research information on the layout and dimensioning of the discontinuity to ensure the interception of air in pipelines is lacking. This paper discusses experimental and numerical model assessments undertaken to compile provisional guidelines for determining the dimensions of the required discontinuity.
Definition and application of a cohesive crack model allowing improved prediction of the flexural capacity of high-performance fibre-reinforced concrete pavement materials : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 54, pp 101 –111 (2012)More Less
In conventional concrete pavement design methods the design parameters are determined using linear elastic analysis. Concrete is subject to significant size effect and as a result linear elastic design concepts, such as the modulus of rupture determined for a beam, have limited reliability in the design of elements of different size and geometry. The objective of this paper is to demonstrate that, in contrast to the modulus of rupture, fracture mechanics material parameters can be used to accurately and precisely predict the flexural capacity of elements of a different size and geometry. The experimental framework includes two high-performance fibre-reinforced concrete mix designs, used to produce beams of different sizes tested in three-point bending configuration, as well as centrally loaded round panels. The fracture energy of the material is determined from the flexural beam tests. An adjusted tensile splitting test procedure is used to determine the tensile strength. The flexural tests on the beams and panels are simulated numerically using two finite element implementations of a cohesive crack approach. The numerical simulation yields satisfactory prediction of the flexural behaviour of the beam and disk specimens. It is concluded that using a fracture mechanics approach, the flexural behaviour of structural elements of different size and/or geometry can be reliably predicted.
Prediction of the debonding / slip load of composite deck slabs using fracture mechanics : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 54, pp 112 –116 (2012)More Less
The aim of this paper is to develop equations that can be used to predict the load at which debonding or slip occurs in composite deck slabs, failing as a result of shear bond rupture. Debonding is the separation of the bonded steel plate from the concrete. The expressions are based on end-slip of the shear span occurring prior to ultimate load. Shear bond failure is considered to be a result of breakdown of mechanical and frictional resistance force between the steel and the concrete interface. Linear elastic fracture mechanics (LEFM) is assumed and the eccentric axial force transmitted by the steel deck is calculated using rotational congruence. The theoretical debonding load results are found to be comparable with experimental results, and to be of use in formulating the response of composite slabs when subjected to fatigue load.
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 54, pp 117 –125 (2012)More Less
A number of pedological soil classification systems have been developed worldwide. These include an internationally accepted system and various national systems, some of which have been incorporated into databases which include maps. Such information is used primarily for agricultural purposes. Various physical and chemical soil properties are used for classifying soils according to these pedological systems. This paper proposes an approach, based on a research project, which may be used to statistically significantly determine the plasticity characteristics of soils from the physical and chemical properties that are used to pedologically classify soils by systems, such as the South African Binomial System. These plasticity characteristics may be used to establish the engineering soil classification groups which may, in turn, be used as a means of rapidly determining the general suitability of areas for proposed developments, particularly during the preliminary stages of transportation route locations and township developments, with a resultant saving of time and money.
The importance of plane end-bearing surfaces when measuring the strengths of concrete core specimens : technical noteAuthor D. KrugerSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 54, pp 126 –127 (2012)More Less