Browsing by Author "Van Zijl, G. P. A. G."
Now showing 1 - 3 of 3
Results Per Page
- ItemDynamic behaviour of normally reinforced concrete wind turbine support structures(South African Institution of Civil Engineering, 2015-12) Van Zyl, W. S.; Van Zijl, G. P. A. G.ENGLISH ABSTRACT: Transportation logistics of large steel towers have led to concrete towers becoming a viable option. There are currently no design codes dealing exclusively with the design of concrete wind turbine towers. Wind turbine towers have strict constraints on the fundamental frequency of the tower to avoid resonance. This paper investigates the dynamic behaviour of wind turbine towers using nonlinear finite element modelling. Focus is placed on the effect of crack formation and soil stiffness on the fundamental frequency of the tower. An analytical model is then proposed that can be used in the primary design stage to determine the geometry of the tower that satisfies the fundamental frequency requirements.
- ItemManufacturing processes for engineered cement-based composite material products(Stellenbosch : University of Stellenbosch, 2004-12) De Koker, Don; Van Zijl, G. P. A. G.; University of Stellenbosch. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: The effort to modify the brittle behaviour of plain cement materials such as cement pastes, mortars and concretes has resulted in the modern concepts of fibre reinforcement and matrixfibre interface engineering. The behaviour of such modern cement-based materials is characterized by a more ductile post-peak softening in uni-axial tension compared with the plain, unreinforced matrix. This is as a result of balancing the matrix strength and toughness with fibre bond and strength. The mechanical response shows a sustained or even higher tensile load carrying capacity after first cracking of the matrix. This class of fibre reinforced composites, designed to exhibit such pseudo-strain hardening properties based on micromechanical principles, are referred to as engineered cement-based composites (ECC). ECC are manufactured by either cast moulding, extrusion or spinning (in the case of pipes). Different manufacturing techniques lead to different performance of composites. Researching the micro-mechanical aspects of ECC, particularly fibre orientation and fibrematrix interfacial bond strength, leads to a better understanding of the strength characteristics and mechanical behaviour. Moreover, the manufacturing process significantly influences these characteristics. Here lies the focus of this research. The research consisted of an in-depth research, literature study and understanding of ECC technology, developing extrusion and cast equipment, developing laboratory testing equipment for pipe testing, tailoring the ECC mix for the specific purpose of manufacture, manufacturing of ECC plate and pipe samples, testing of ECC for various manufacturing techniques and scrutinising/ analysing the results for recommendations with respect to further research and commercialisation of ECC material products.
- ItemA study on the design and material costs of tall wind turbine towers in South Africa(South African Institution of Civil Engineering, 2015) Way, A. C.; Van Zijl, G. P. A. G.ENGLISH ABSTRACT: The aim of this project was to study the structural design and material costing of various designs of tall wind turbine towers and the associated foundations in a South African context. Design guidelines are proposed for the design of tubular steel, concrete and concrete-steel hybrid towers and foundations for hub heights of 80, 100 and 120 m. The results indicate that concrete and hybrid towers become viable alternatives to the conventional steel towers at hub heights equal to and above 100 m. Three heights – 80 m, 100 m and 120 m – of each type of tower (steel, concrete and hybrid) and their foundations were designed according to the relevant design standards. The designs were verified using the Abaqus CAE finite element software (SIMULIA 2010). The material costs of the designs were calculated for a South African environment, according to the increases in material cost with increasing hub height. In this paper, the required foundation sizes for the concrete and hybrid towers were found to be smaller than for the steel towers. The material costs of the concrete and hybrid towers were shown to be lower than for the steel towers, especially at hub heights above 100 m. An increase in hub height caused an increase in energy generation of 3.52% and 6.28% for 80 m to 100 m, and for 80 m to 120 m hub heights, respectively. It is postulated that the concrete and hybrid towers become viable alternatives to the conventional steel towers at hub heights above 100 m.