No description available.

Thesis (MScEng)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

An integrated computer model for time and cost optimisation has been developed for multi-storey reinforced concrete office buildings. The development of the model has been based on interviews completed with Planners, Estimators and Researchers within 2 of the top 20 (in terms of turnover) UK main contractors, and on published literature, bar charts and bills of quantities of concrete framed commercial buildings. The duration and cost of construction of a typical multistorey reinforced concrete office building is calculated through the first part of the integrated model, i.e. the simulation model. The model provides a set of choices for the selection of materials and plant and possible methods of work. It also requires the user to input the quantities of work, gang sizes and the quantity of plant required, lag values between activities, output rates, unit costs of plant, labour costs and indirect costs. A linked bar chart is drawn automatically by using the data available from the simulation model. The second part of the model, (optimisation) uses the data provided by the simulation part and provides sets of solutions of time vs. cost from which the minimum project cost corresponding to the optimum project duration is calculated under the given schedule restrictions. Linear programming is used for the optimisation problem. The objective function is set to be the minimisation of the project cost which is the total of the direct costs of all the activities creating the project and the indirect costs of the project. The constraints are formulated from the precedence relationship, lag values, and normal and crash values of time and cost for the activities supplied by the simulation model. The simulation part has been validated by comparing and contrasting the results with those methods and practices adopted by commercial planners and estimators. The validation of the optimisation part has been undertaken by plotting time-direct cost curves from the results and checking the convexity of the curves. Additionally, the validation procedures included taking account of the opinions of practitioners in the industry on the practical and commercial viability of the model.

abstract: The concept of Creep is a term used to define the tendency of stressed materials to develop an increasing strain through time under a sustained load, thus having an increase in deflection or having an elongation with time in relation to the short term strain. While the subject of compression creep of concrete is well developed, use of concrete under tension loads has been limited at best due to brittleness of concrete. However with the advent of using fiber reinforced concrete, more and more applications where concrete is expected to carry tensile loads due to incorporation of fibers is gaining popularity. While the creep behavior of concrete in tension is important, the main case of the study is what happened when the concrete that is cracked in service is subjected to sustained loads causing creep. The relationship of opening cracks under these conditions are of utmost importance especially when the serviceability criteria is addressed. Little work has been reported in literature on the long-term behavior of FRC under sustained flexural loadings. The main objective of this study is to investigate the Long Term Flexural Behavior of Pre-Cracked Fiber Reinforced Beams under Sustained Loads. The experimental reports document the effect of loading and temperature on the creep characteristics of concrete. A variety of study has been carried out for the different responses generated by the creep tests based on factors like effect of temperature and humidity, effect of fiber content, effect of fiber type, and effect of different loading levels. The Creep Testing Experimental Methodology is divided into three main parts which includes: (1) The Pre-cracking Partial Fracture Test; (2) Creep Test; (3) Post Creep Full Fracture Test. The magnitude of load applied to a specific specimen during creep testing was based on the results of average residual strength (ARS) tests, determined using EN14651. Specimens of the synthetic FRC mixture were creep tested at loads nominally equivalent to 30% and 50% of the FR1 value. The creep tests are usually continued until a steady Time versus CMOD response was obtained for the specimen signifying its presence in the secondary stage of creep. The creep recovery response is generated after unloading the specimen from the creep set up and later a full fracture test is carried out to obtain the complete post creep response of the beam under flexure. The behavior of the Creep Coefficient versus Time response has been studied using various existing models like the ACI 209-R 92 Model and the CEB-FIP Model. Basic and hybrid rheological viscoelastic models have also been used in order to generate the material behavior response. A study has been developed in order to understand the applicability of various viscoelastic models for obtaining the material response of real materials. An analytical model for predicting the Flexural Behavior of FRC under sustained creep loads is presented at the end. This model helps generate the stress strain and Moment Curvature response of FRC beams when subjected to creep loads post initial cracking / Dissertation/Thesis / Masters Thesis Civil Engineering 2017

Blocos sobre estacas ou blocos de coroamento são elementos estruturais usados para transferir as ações da superestrutura para um conjunto de estacas. São encontrados em infra-estruturas de pontes e edifícios. O conhecimento de seu real comportamento estrutural é de fundamental importância, pois são elementos estruturais que garantem a segurança de toda a estrutura. Ainda não há consenso no meio técnico quanto ao seu real comportamento estrutural; também não se sabe a real forma geométrica das bielas de compressão no Estado Limite Último para a aplicação do método biela-tirante, e falta normalização deste elemento estrutural; estes são alguns aspectos que tornam este trabalho necessário. Com o objetivo de contribuir para diretrizes de projeto, foram apresentados os critérios utilizados nos projetos de blocos sobre estacas e desenvolvido, por meio de resultados de modelos analíticos, um método para a verificação da tensão de compressão na biela junto ao pilar. Nos modelos adotados variaram-se os diâmetros de estacas e dimensões de pilar. Conclui-se que os resultados são de grande relevância, pois os resultados obtidos mostraram-se muito coerentes por serem constantes em função da quantidade de estacas e da relação x/d. / Piles caps are structural elements used to transfer actions of the superstructure to a group of piles. They are found in infrastructures of bridges and buildings. The knowledge of its real structural behavior presents fundamental importance, once piles caps are structural elements that guarantee the safety of all structure. There is no consensus yet between specialists on its real structural behavior, the real geometric shape of the struts on the ULS for the application of the strut-and-tie model its not know, and the lack of standardization of this structural element are some of the aspects that makes this work necessary. With the objective to contribute to the design guidelines, were presented the criteria used in projects of piles caps and developed through results of analytical models, a method for checking the compressive stress at the strut near the column. Piles diameters and column dimensions of the models were been varied. It was concluded that the results are of great relevance, because the values obtained proved to be very consistent since they are in depending on the amount of piles and the relationship x/d.

Neste trabalho são apresentados procedimentos para o dimensionamento de elementos de chapa de concreto armado com armaduras em malha ortogonal, com as direções não coincidentes com as das tensões principais. É feita uma revisão dos conceitos teóricos do Método de Baumann e do Modified Compression Field Theory, sendo que no primeiro foi incorporada a relação tensão-deformação do concreto fissurado proposta por Vecchio e Collins. Para a análise das deformações principais é feita uma revisão do estado duplo de deformações utilizando-se o círculo de Mohr. Posteriormente são feitas comparações entre os resultados de modelo físicos e as formulações analíticas, bem como entre os resultados de modelos hipotéticos utilizando ambos os métodos, com o objetivo de valorizar o Método de Baumann dada a sua simplicidade, mostrando que este apresenta resultados a favor da segurança. Buscou-se através do Método de Baumann avaliar os benefícios da utilização de armaduras de compressão. / Procedures are presented for the reinforced concrete membranes design with orthogonal mesh, which does not coincide with principal stress directions. A review of the theoretical fundamentals for Baumann Method and Modified Compression Field Theory is presented, and in the first was used the stress-strain relationships for the cracked concrete developed by Vecchio and Collins. A review of the plane strain is presented using the Mohr Circle for the principal strains analysis. Later, the results of tested panels and the theoretical formulations are compared, also between hypothetical panels using both methods, to enhance the Baumann Method due its simplicity, ensuring that presents overestimated results. Benefits were evaluated through Baumann Method using compression reinforcement.

M.Ing. / Design parameters for ferritic type stainless steel structural members do not exist and is needed. This study attempts to find design parameters for ferritic type stainless steel compression elements. The ferritic type stainless steel under consideration in this study is Type 3CR12 corrosion resisting steel, which is a modified Type 409 stainless steel. The purpose of this study was to determine the limiting web width-to-thickness and flange width-to-thickness ratios for the prevention of local buckling in axially loaded hotrolled Type 3CR12 corrosion resisting steel columns. Experimental data was obtained in an ongoing study on the limiting width-to-thickness ratios for elements in compression. No conclusion on this aspect can be reached at this stage of the investigation

No description available.

Explosives place large demands on the lateral load carrying capacity of structures. If these loads are applied on columns, the high pressure transient loads from explosives can result in significant damage to the primary gravity load carrying elements. The loss of these elements, which are responsible from overall strength and stability of the structure, may cause collapse of all or parts of the structure. Therefore, it is important to mitigate the blast loads effects on columns. A comprehensive research study into the design, application, and use of different retrofit systems to mitigate damage to columns under blast loads has been undertaken. This research program, consisting of experimental testing and analytical investigation, sought out retrofits that address the strength of columns as well as those that enhance ductility are explored. Different materials and resistance mechanisms are used to increase column capacity. An experimental testing program was conducted using a shock tube to test the capacity of columns under blast loads. For this program, a total of sixteen reinforced concrete columns were constructed and the data from a further two columns from a previous study was compiled. Of these columns, a total of thirteen were retrofitted to mitigate the effects of blast. Carbon fibre reinforced polymer (CFRP) was applied to eight of the columns in the form of jacketing, longitudinal reinforcement, or the combination of the two. The other retrofits included steel prestressed confinement applied to one column, steel bracing acting as compression members applied to one column, and steel bracing acting as tension members applied to three columns. The columns were tested under incrementally increasing shock tube induced shock wave loading up to failure of the specimen or capacity of the shock tube. The performance of the retrofitted columns was compared with the control columns and against other retrofits. Quantitative comparisons of displacements and strains were made along with qualitative assessments of damage. The results indicated that all the retrofits increased capacity to the column, however, certain retrofits out performed others. The best FRP retrofit technique was found to be the combination of longitudinal and transverse FRP. The prestressed steel jacketing proved to be effective at increasing ductility capacity of the column. The compression brace retrofit was found to be effective in significantly increasing capacity of the column. The tension brace retrofits had the best performance over all the retrofits including the compression brace retrofit. The experimental data was used to validate analysis techniques to model the behaviour of the specimens. This technique reduced the columns to an equivalent single-degree-of-freedom (SDOF) system for dynamic analysis purposes. The reduction to the SDOF system was achieved by computing a resistance to lateral load and lateral displacement relationship. Each retrofit was carefully considered in this analysis including the retrofit’s possible effect on material and sectional properties as well as any force resistance mechanism that the retrofit introduces. The results of the modeling and experimental program were used to develop retrofit design guidelines. These guidelines are presented in detail in this thesis.

Ambient vibrations of a reinforced concrete tower structure were recordedand analyzed to obtain the natural frequencies, the associated mode shapes and an estimate of the equivalent viscous damping. The structure investigated consists of four concrete wall panels,rigidly connected at various levels and contains a light precast concrete stairwell. It is similar to typical components of larger structures,such as stairwells and elevator shafts or cores. The given information should be useful in offering details of the dynamic behaviour of this type of structural elements. The experimental results are compared with the theoretical results obtained from two- and three-dimensional dynamic analyses using matrix methods applied to linear elastic systems with lumped masses. An efficient computer program to find the eigenvalues and eigenvectors for this type of mathematical model is described. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate