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- Volume 49, Issue 2, 2007
Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese - Volume 49, Issue 2, 2007
Volumes & issues
Volume 49, Issue 2, 2007
Sand transport at and shoreline response to a breakwater attached to a large tidal pool at Monwabisi, Cape Town : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 49, pp 2 –9 (2007)More Less
A beach has formed in the lee of a breakwater (spur: rubblemound structure built parallel to the shoreline) attached to the eastern side of the Monwabisi tidal pool, which is located along the shoreline of northern False Bay near Cape Town. The sediment transport regime at Monwabisi is described in terms of the longshore sand transport, an eddy current that forms in the lee of the spur, the effect of wave reflection against a steep slope, transport through the spur, and wind-blown sand transport. The accretion and stability of Monwabisi beach were investigated by analysing photographs, five topographic surveys, cross-sections, and loss/gain maps from these surveys. Large accretion of sand (in total about 32 000 m3 and up to about 2,5 m vertically) occurred mainly alongside the eastern tidal pool wall and between the original shoreline and the spur. The beach slope varies considerably along Monwabisi beach: from 1:66 to 1:8. Beach profile changes occurred up to a level of +3 m. The beach reached equilibrium approximately 2,5 years afterconstruction of the spur started.
Evaluation of the effect of suretyship on rapid delivery public sector construction projects : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 49, pp 10 –15 (2007)More Less
Suretyship is one of the performance risk management measures used in modern construction contracts. Construction contracts, such as the FIDIC, JBCC Series 2000 and GCC 2004, offer pro forma deeds of suretyship and guarantee forms, but consultants sometimes use in-house contract documentation, which may lead to poor interpretation and application.
Suretyship requirements are often the cause of time delays on Rapid Delivery Public Sector Construction Projects (RDPSCP), whether pro forma or in-house deeds or forms are used. Project start dates are generally set within weeks after the contract has been awarded, which time period may be inadequate for some contractors (more specifically emerging contractors) to provide a surety to the approval of the client. In the event of non-performance by the original contractor another contractor must be appointed to complete the works. This process results in loss of time attributable to time frames required for issuing contractual / statutory notices to the original contractor, and delay in appointing a second contractor.
Most general conditions of contract have been designed from a commercial and legal perspective, which ignore the negative practical implications of construction suretyship on progress on site. Consultants, therefore, are compelled by necessity to draft special conditions to suit RDPSCP, otherwise delays and disputes are inevitable.
It is recommended hereafter that, instead of sureties, guarantees be used as securities, which should be in the form of a 'demand guarantee'. No construction time will be lost in calling up this type of construction guarantee (Forsyth & Pretorius 2002: 26) as the guarantor unconditionally and irrevocably undertakes to pay the amount of guarantee on demand and without proof of any breach of contract by the contractor.
Characterising the shear behaviour of strainhardening fibre-reinforced cement-based composites : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 49, pp 16 –23 (2007)More Less
Strain-hardening fibre-reinforced cement-based composites (SHCC) are a class of fibre-reinforced concrete (FRC) that, reinforced with relatively low volumes of short fibres, exhibit strain-hardening, tough tensile and flexural response. These qualities hold promise also for ductile, superior shear behaviour, which has been demonstrated in experimental projects internationally. The potential reduction or elimination of conventional steel shear reinforcement in reinforced concrete by the use of FRC, and in particular SHCC, is an example of how the tensile ductility properties of SHCC may be exploited. Other uses include generally improved ductility and durability of structures by selective use of these superior construction materials. However, the true shear behaviour of SHCC is not yet understood and analytical and design models have not yet been formulated due to a lack of an appropriate, accurate direct shear test method. This paper describes the investigation of the shear properties of SHCC. A modified Iosipescu shear test is developed for SHCC by finite element analysis. An experimental program of shear tests is subsequently reported, which aims to characterise the true shear mechanisms and properties of SHCC.
A computational model for strain-hardening fibre-reinforced cement-based composites : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 49, pp 24 –31 (2007)More Less
The development of a computational model based on a computational continuum damage formulation for a class of strain-hardening fibre-reinforced cement-based composites (SHCC) is reported on. Particular features of SHCC mechanical behaviour, namely multiple cracking at increasing stress levels with successive cracking, and eventual failure at a single crack, require incorporation of strain-hardening and strain-softening beyond threshold levels of damage evolution. A localisation zone length scale is incorporated, related to the physical failure phenomenon of fibre pull-out in the final failure crack in SHCC. Thereby, the computational solution is regularised, causing it to become finite element mesh size-independent. A novel equivalent strain criterion is formulated, whereby the predominantly tensile (mode 1)-dominated damage formulation is improved to also capture shear-dominated (mode 2) failure with reasonable accuracy. The model is verified by finite element analysis of flexural and shear laboratory experiments performed at the Institute for Structural Engineering, University of Stellenbosch.
Linkages between solar activity, climate predictability and water resource development : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 49, pp 32 –44 (2007)More Less
This study is based on the numerical analysis of the properties of routinely observedhydrometeorological data which in South Africa alone is collected at a rate of more than half a million station days per year, with some records approaching 100 continuous years in length. The analysis of this data demonstrates an unequivocal synchronous linkage between these processes in South Africa and elsewhere, and solar activity. This confirms observations and reports by others in many countries during the past 150 years. It is also shown with a high degree of assurance that there is a synchronous linkage between the statistically significant, 21-year periodicity in these processes and the acceleration and deceleration of the sun as it moves through galactic space. Despite a diligent search, no evidence could be found of trends in the data that could be attributed to human activities.
It is essential that this information be accommodated in water resource development and operation procedures in the years ahead.
Postulates on shear in reinforced concrete In Journal of the South African Institution of Civil Engineers 48 (4) 2006, pp.45-48 : discussionSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 49, pp 45 –48 (2007)More Less