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- Volume 52, Issue 2, 2010
Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese - Volume 52, Issue 2, 2010
Volumes & issues
Volume 52, Issue 2, 2010
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 52, pp 2 –11 (2010)More Less
Large span concrete flat-slab systems with internal spherical void formers (SVF) have been used in Europe for over a decade. They are bi-axially reinforced concrete flat-slab systems with a grid of internal spherical void formers.
This paper addresses three issues associated with SVF slab systems: their shear resistance, their short-term elastic deflections and their economical value in a South African context.
Due to the ''loss'' (or reduction) of aggregate interlock required for shear resistance in SVF slabs, the design requirements of the reinforced concrete design code are affected. Research at the Technical University of Darmstadt (TUD) in Germany proved a shear resistance reduction factor of 0,55 to be conservative, while research at the University of Pretoria suggests a greater factor of 0,85 when taking into account the shear capacity of the permanent steel cages that hold the spheres in position in some SVF slab systems.
Laboratory tests at the TUD, supported by theoretical calculations, further showed reduced deflections for SVF slabs compared to solid slabs. Stiffness is not reduced as much as the selfweight, resulting in smaller overall deflections for SVF slabs compared to those of solid slabs with the same thickness.
In this paper the economical value of SVF slabs in South Africa will be investigated by comparing the direct construction cost to that of two other large span slab systems, namely coffer and post-tensioned slabs.
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 52, pp 12 –18 (2010)More Less
Response sensitivity analysis as a part of dynamic finite element structural analysis has many applications to structures of realistic scale and complexity in earthquake engineering. A demonstration project, consisting of a hospital structure and piping network, is used to demonstrate the potential applications of the method to practical problems. Nonlinear finite element analysis is done to determine displacements, stresses, etc, as well as sensitivity information by the direct differentiation method. The response sensitivity analysis is used for the identification of critical parameters of the systems, optimisation, calibration and the generation of fragility curves.
Numerical modelling for the evaluation of progressive damage to plain concrete structures : technical paperAuthor S.A. SadrnejadSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 52, pp 19 –30 (2010)More Less
Among the various numerical simulation models of plain concrete, the micro-plane models perform exceptionally well. They are not as complicated as the microscopic models, such as the discrete particle models, and do not have the shortcomings of the macroscopic models based on stress or strain invariants. The constitutive equations for the mechanical behaviour of concrete, capable of predicting damage effects or crack growth under loading, unloading or reloading, were developed on a micro-plane framework. The proposed damage formulation is based on combinations of five fundamental types of stress / strain, which essentially may occur on any of the micro-planes. Model verification was done using different loading, unloading and reloading stress / strain paths. The proposed model is capable of yielding a pre-failure/post-failure history of stress / strain on different predefined sampling planes through material. This micro-plane damage model of plain concrete was developed in a 3D finite element code to show its abilities in crack / damage analysis and prediction of failure mechanisms as compared with plain concrete tests. The proposed code is able not only to predict the crack path, but also to determine which combination of loading conditions occurs on damaged micro-planes. The validity of the proposed model is investigated through a few test cases and a double curvature arch concrete dam.
Characterising the ductility and fatigue crack resistance potential of asphalt mixes based on the laboratory direct tensile strength testSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 52, pp 31 –40 (2010)More Less
As a means to investigate the applicability of the direct tensile strength (DT) test as a surrogate fatigue crack test, the ductility and fatigue crack resistance potential of various asphalt (HMA) mixes were evaluated in the laboratory using the DT test, at ambient temperature (20°C) and a displacement loading rate of 1,27 mm/min. Various HMA mixes were included in the DT test program and the results were compared with those of the Overlay Tester, also conducted at ambient temperature. Up to 23 commonly used Texas HMA mixes with different mix design characteristics were evaluated and are discussed in this paper. The results indicated that the mix design volumetrics, such as the asphalt binder content and aggregate gradation, play a significant role in the ductility and fatigue crack resistance potential of HMA mixes. The denseto fine-graded HMA mixes with high asphalt binder content exhibited better ductility potential and laboratory fatigue crack resistance than the coarse-and open-graded mixes. Overall, the DT test was found to be a promising surrogate fatigue crack test for mix design and HMA mix screening for fatigue crack resistance in the laboratory. Recommendations to improve the test protocol are included in the paper. However, sample fabrication and test set-up were the two critical issues found to be associated with the DT test.
The status of talent management in the South African consulting civil engineering industry in 2008 : a survey : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 52, pp 41 –47 (2010)More Less
Talent management, an integrated system of recruitment, development and retention of the required human capital at all organisational levels, is at the forefront of business agendas. Given the skills shortage in South Africa, talent management is expected to remain a business imperative especially in the science, engineering and technology arena. The importance of talent management stems from its role in achieving competitive advantage in order to realise the strategy of the organisation. In this paper the perceptions of people responsible for talent management in their respective organisations are presented to determine the status of talent management in the South African consulting civil engineering industry in 2008. The survey found that most respondents (94%) thought talent management was a priority but only 57% of them had some talent management initiative in place. The primary concern (55% of respondents) was to create a deep reservoir of successors at all hierarchical levels of the organisation. Inability to do so threatens not only the continuity of the organisation per se, but also the wealth-creating capacity of the country as a whole, since civil engineers play a primary role in creating and maintaining infrastructure.
Estimation of extreme flood peaks by selective statistical analyses of relevant flood peak data within similar hydrological regions : technical paperAuthor J.H. NortjeSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 52, pp 48 –57 (2010)More Less
This paper describes a new Regional Estimation of Extreme Flood Peaks by Selective Statistical Analyses (REFSSA) method to estimate extreme flood peaks from regional flood peak data. The method differs from current regional flood frequency analysis (RFFA) methods or approaches in that an additional separate statistical analysis is performed on "record maximum flood peaks" within a "similar hydrological region". Suitability of the method is demonstrated for the estimation of extreme flood peaks with annual exceedance probabilities between 0,001 (1/1 000) and 0,0001 (1/10 000) for two major hydrological regions in South Africa, and for catchment sizes between 100 and 7 000 km2. The applicability of the method for catchments outside these regions and limits has not been fully tested mainly due to a shortage of verified data. The theory and a practical example are presented. Excellent results have been obtained so far, displaying high correlation coefficients between extreme flood peak data and regression lines, namely 0,99 on average on log-normal scale. The method is considered to have universal application, especially in climates experiencing outlier type of extreme flood peaks.
Author M. DunduSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 52, pp 58 –64 (2010)More Less
This paper describes tests to determine partial resistance factors that are to be used in designing small steel structures. Several welding skills were incorporated into the investigation so as to come up with different partial resistance factors. Different skills will then be included in the design procedure, allowing the engineer freedom to assess the availability of skills and to specify connection details accordingly. This investigation was carried out using butt and fillet-welded specimens in tension under static loading only. Half of the samples were welded flat and the other half were welded vertical. It is evident from the load-elongation graphs that plastic deformation is more extensive in specimens welded by experienced welders and that specimens welded flat are more ductile than those welded vertical. Vertical welding also resulted in a greater percentage of defects than flat welding. Most of the defects in the welds were a result of incomplete penetration, lack of fusion, slag inclusion, porosity and failure to weld to the given dimensions.
The relationship between index testing and California Bearing Ratio values for natural road construction materials in South Africa : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 52, pp 65 –69 (2010)More Less
Research was done to determine whether a relationship can be established between index testing and CBR (California Bearing Ratio) results. The process involved compiling a database of test results for a range of rock material types across moist and dry regions in southern Africa. The database was compiled in such a way that it represents natural gravels sampled (mostly) for construction or rehabilitation of road layer works. The database included a location description, material description, Weinert N-value, Atterberg Limits, grading analysis and CBR values. In addition, the linear shrinkage product, shrinkage product, grading coefficient, grading modulus and dust ratio were calculated and also used in the analyses. Data were grouped based on climate, rock material type and compaction, and analysed separately. The data were compared with existing prediction models, after which linear and Weibull regressions were performed to derive new models. Over 130 regressions were derived. The results proved poor and this is ascribed to data variability. The data variability, in turn, is the result of test methods with poor reproducibility and repeatability. In short, the test methods (the CBR in particular) resulted in inconsistent data and subsequently poor results, making accurate predictions nearly impossible.
Author D.P.G. De WetSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 52, pp 70 –76 (2010)More Less
Weigh-in-motion (WIM) scales are installed on various higher order roads in South Africa to provide traffic loading information for pavement design, strategic planning and law enforcement. Some WIM systems produce anomalies that cannot be satisfactorily explained even by highly experienced professionals. Much of the problem relates to the difficulty in determining the appropriate calibration factors to correct systematic measurement error for WIM systems and the inadequacy of data quality management methods. The author has developed a post-calibration method for WIM data, called the Truck Tractor (TT) method, to correct the magnitude of recorded axle loads in retrospect. In addition, it incorporates a series of data quality checks. The TT method is robust, accurate and adequately simple for use on a routine basis for a wide variety of South African WIM systems. The calibration module of the TT method (i.e. the procedure to determine the calibration factor, kTT) has been accepted by SANRAL and incorporated into the model it uses to quantify the cost of overloading on toll concessions. Some of the data quality checking concepts are also being considered for further use and threshold values for tests are being refined by SANRAL for this purpose.
Evaluation of recycled water recovered from a ready-mix concrete plant for reuse in concrete : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 52, pp 77 –82 (2010)More Less
A study was conducted into the quality of recycled water at a ready-mix concrete plant to determine its suitability as mixing water for concrete. Concrete mixes made at a water/ cementitious ratio (w/cm) of 0,5, with or without 50% ground granulated blast-furnace slag, and mortars of 0,47 w/cm were prepared using municipal and recycled water. Recycled water was used to replace municipal water at various proportions of 0, 30, 50 and 100%, then used as mix water. Tests were done on fresh and hardened concretes and mortars. The chemical impurities present in the recycled water satisfied the limits given in SANS 51008 /EN 1008 and ASTM C 94 for mix water. The use of recycled water as mix water led to a slight reduction in slump of concrete or flow of mortar. Hydration heat output and air permeability were not affected, and mortar compressive strengths increased with a rise in the proportional amount of recycled water used in the mix. In mortars, the use of 100% recycled water gave a substantial increase in strengths of up to 8%. Within the limitations of this study, it was found that recycled water from ready-mix concrete plants can be suitable for use as mix water in concrete-making.
Practical implications of the relation between the clay mineral content and the Plasticity Index of dolerite road construction material : discussionSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 52, pp 83 –84 (2010)More Less