Under seismic excitation, the centre of stiffness of an eccentric structure is stationary as long as the structure remains elastic. Once yielding occurs, the centre of stiffness will begin to move away from its original position, as the torsional forces induced by the eccentricity cause uneven distribution of yielding among members. This movement of the centre of stiffness very often increases the eccentricity of the structure causing further damage. The purpose of this thesis is to determine the significance of this magnification of the initial eccentricity. A procedure for locating the centre of stiffness was developed and incorporated into a time-step dynamic analysis program code named DRAINTABS. Two models were chosen to describe the moment-rotation relationship of reinforced concrete members; the elasto-plastic model and the Takeda model. The former is a bilinear model whereas the latter takes into account the strength degradation of reinforced concrete members under cyclic loading. A number of reinforced concrete buildings were studied. It was found that the centre of stiffness did not always move towards the side of the structure which was more heavily loaded due to the torque induced by the eccenticity. Excursions in the other direction were possible when the translational motion was not in phase with the torsional motion at the instant of maximum excursion. Moreover, when the strength degrading characteristic of R/C members was modelled, the eccentricity of the structure increased gradually with increasing length of excitation. However, this increase was found to be small and therefore insignificant. The procedure for locating the centre of stiffness was also incorporated into another analysis program code named PITSA which utilizes the modified substitute structure method. The results obtained were compared to those obtained using DRAINTABS. Although PITSA has been proven to be a relatively inexpensive yet reliable alternative to a time step analysis, it failed to predict the maximum displacement of the centre of stiffness with any acceptable degree of accuracy. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The influence of reversed low cyclic loading on the bond behaviour of deformed bars in plain as well as steel-fiber-reinforced concrete has been studied experimentally and is discussed in this thesis. In total, ten specimens consisting of two plain concrete and eight steel-fiber reinforced specimens were tested to failure. The variables were the mix proportions, the size and shape of the steel fibers and the pattern of loading. The results indicate that the most important factor affecting bond or stress transfer is the peak stress reached in the previous cycle. It was observed that steel-fiber-reinforced concrete exhibits higher bond strength, improved stiffness and less bond-deterioration under reversed cyclic loading than plain concrete. It was also found that steel fibers make a definite contribution to crack control and better serviceability. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

D.Ing. (Civil Engineering) / Polypropylene (PP) fibre is one of the most widely used fibres for reinforcing concrete. Due to its unique material properties such as economic production cost, relatively high melting point and alkaline resistance, PP fibres in concrete are found to increase the toughness, provide restrained plastic and drying shrinkage cracking resistance, increase impact resistance and flexural loading capacity (especially during the post-crack stage) of concrete structures and components. The wettability of PP fibre surfaces is poor due to the hydrophobic surface nature of polypropylene. The bonding between the PP fibre and the concrete matrix is recognized as poor and currently the PP fibre / concrete interfacial bonding depends upon interlocking and keying (mechanical bonding). As the interfacial bond strength between the PP fibre and the concrete is much smaller than the tensile strength of PP fibre and concrete, in order to fully explore the reinforcing effect of PP fibres in concrete, further improvement of interfacial bonding is necessary. In this investigation, the research work was conducted on the surface oxyfluorinated PP fibre newly developed by the Atomic Energy Corporation of South Africa Limited. Examining the feasibility of using this fibre in concrete, as well as evaluating its superiority over unmodified PP fibres, is the key task of this investigation. This new type of oxyfluorinated PP fibre shows a large increase in interfacial bond strength compared to the unmodified PP fibres. The surface free energy concept and Lewis acid-base interfacial interaction theory were innovatively used to examine the interfacial bonding between the PP fibre and the concrete matrix. The purpose of this study was to develop the background of such oxyfluorinated PP fibres, to establish the mechanism of the increase in interfacial bonding and to investigate the basic properties of the concrete incorporating oxyfluorinated PP fibres. The experimental results on the properties of oxyfluorinated PP fibre reinforced concrete compared with those of unmodified PP fibre reinforced concrete and plain concrete are presented, with some field test results focused on the improvement in shrinkage cracking control capacity. It is concluded in this investigation that the surface oxyfluorinated PP fibres possess significantly increased PP fibre / concrete interfacial bonding due to the chemical bond arising from the acid base interfacial interaction and the intimate interfacial contact arising from the improved fibre surface wettability. When combining oxyfluorinated pp fibre with concrete, a general improvement in the physical and mechanical properties of fibrous concrete compared to that created with unmodified PP fibres, is obtained.

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The purpose of this paper is to present the development and use of a computer program to perform an automated structural design of two dimensional static concrete structural systems. The structural systems considered herein are composed of reinforced concrete beams and columns connected by rigid joints. Structural systems composed of large numbers of joints and members may be analyzed by using the developed program. The paper presents the development of the structural analysis using the displacement method and matrix techniques and the development of the concrete axial-moment interaction criteria. This criteria is based on the ultimate strength design using the 1971 ACI Building Code requirements. A detailed sample problem of a four story concrete building structure is presented. The sample problem gives the details of computer program input and output. The presented computer program is written FORTRAN language.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The Department of Water Affairs and Forestry infrastructure has shown a decline in condition from 2006 to 2011, according to the Infrastructure Report Card. With the increase in population, the additional demand placed on the already ageing infrastructure together with inadequate maintenance exacerbates the deterioration of these structures. Much has been done to improve the provision of basic water services to South Africans, however to ensure that basic water services remain intact, maintenance of the existing structures is of paramount importance. The storage of potable water in a hygienic manner is essential to the water provision network, thus focus is placed on water reservoirs (in particular reinforced concrete water reservoirs). It has been identified that there is a lack of appropriate policies, practices, procedures and guidelines related to the maintenance of municipal water reservoirs. The solution that this study proposes is to develop a maintenance prioritization method for reinforced concrete water reservoirs. This method specifically provides the user (i.e facility manager) with a systematic approach to assessing and allocating a condition value to the reservoir, which is used to prioritize maintenance activities. This method follows the approach used by the TRH/TMH manuals and bridge management systems that are implemented throughout South Africa. This method includes, the breakdown of essential reservoir components thus facilitating the development of future asset registers, the deterioration mechanisms that affect these reservoirs along with the appropriate identification methodologies and the percentage contributions of each component to the overall condition of the facility. The research for the prioritization method is conducted by combining literature with feedback from industry professionals. The literature featured investigation of the components of concrete reservoirs and deterioration mechanisms that affect these components. The results of the feedback from the industry professionals indicated that some of the components contribute more to the overall condition of the facility than others. This contribution is based on the importance of the component with regard to the provision of service and safety. Thus, in the case of a concrete reservoir, the walls are more essential to the provision of service and safety than the access components, thus its contribution percentage is higher. The research suggests that if the prioritization method could successfully be implemented, it will provide the users additional information that can be used to prioritise maintenance activities at both component and network level. Further, it may allow for the development of a comprehensive asset register of concrete reservoirs and may also aid in the financial planning related to the maintenance of these structures. / AFRIKAANSE OPSOMMING: Die Departement van Waterwese en Bosbou se infrastruktuur het n afname in kondisie gradering getoon van 2006 tot 2011 volgens die Infrastruktuur Verslag Kaart. Die toename in die bevolking veroorsaak bykomende druk op die reeds verouderende infrastruktuur wat tesame met swak instandhouding die agteruitgang van hierdie strukture vererger. Baie is gedoen om die voorsiening van basiese waterdienste aan Suid-Afrikaners te verbeter, maar dit is uiters noodsaaklik dat bestaande strukture in stand gehou word om te verseker dat basiese waterdienste beskikbaar bly. Die berging van drinkwater op ’n higiëniese wyse is noodsaaklik vir die watervoorsieningsnetwerk met die gevolg dat daar op waterreservoirs, spesifiek gewapende beton waterreservoirs, gefokus word. Daar is vasgestel dat daar nie toepaslike praktyke, prosedures en riglyne met betrekking tot die instandhouding van van munisipale waterreservoirs bestaan nie. Die oplossing wat deur hierdie studie voorgestel word, is om ’n onderhoud prioritisering metode vir gewapende beton waterreservoirs te ontwikkel. Hierdie metode bied spesifiek aan die gebruiker (reservoir bestuurder) ’n sistematiese benadering om ’n toestandwaarde ten opsigte van die reservoir te bepaal en toe te wys, wat gebruik word om instandhoudingsaktiwiteite te prioritiseer. Hierdie metode volg die benadering van die TRH/TMH en brug bestuur sisteme, wat geimplimenteer word reg deur Suid Afrika. Hierdie metode sluit in die klassifiseering van hoof komponente van ’n gewapende beton reservoir wat die ontwikkeling van toekomstige bateregisters, die degenerasiemeganismes wat hierdie reservoirs beïnvloed tesame met die gepaste identifiseringsmeganismes en die bydrae volgens persentasie van elke komponent tot die algehele toestand van die fasiliteit, fasiliteer. Die navorsing ten opsigte van die prioritiserings metode is uitgevoer deur literatuur met terugvoer van bedryfskundiges te kombineer. Die literatuur wat geraadpleeg is handel oor die ondersoek na die komponente van gewapende beton reservoirs en degenerasiemeganismes wat hierdie komponente beïnvloed. Die studie dui aan dat, aan die hand van die bedryfskundiges se terugvoer, sommige komponente meer as ander tot die algehele toestand van die fasiliteit bydra. Hierdie bydrae is gebaseer op die belangrikheid van die komponent in terme van die voorsiening van dien ek veiligheid. Dus, is die geval van n beton reservoir, is die mure meer van beland as die toegans komponente in terme van voorsiening van diens en veiligheid. Die navorsing gee te kenne dat indien die prioritiserings metode suksesvol geïmplementeer kan word, dit die gebruiker bykomende inligting kan gee wat gebruik kan word om die instandhoudingsaktiviteite te prioritiseer op beide netwerk en komponente vlak. Verder, mag daar ’n omvattende bateregister van gewapende beton reservoirs ontwikkel kan word wat dus sal help met die finansiële beplanning rondom die instandhouding van hierdie strukture.