M.Ing. (Civil Engineering) / Please refer to full text to view abstract

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

The main objective of this study was to determine whether Limit Design could be applied to low-rise unbraced concrete frames. The investigation was carried out both analytically and experimentally. In the analytical part, two mathematical models were used to determine the behavior of unbraced frames. The first method used a nonlinear computer program, which takes into account the material and geometric nonlinearities of concrete frames. Several cases of frames with different reinforcement ratios and under different beam to column load ratios were investigated. For each frame the gravity loads were increased proportionately to 3/4 of the ultimate frame capacity. Then, lateral load was applied to failure while keeping the beam and column loads constant. The second mathematical model solved for the frame stability equation by assuming elasto-plastic moment curvature relationships for members. Also, the stability solution was carried out by reducing the frame to a column attached to a linear spring. In the experimental part, two frames were designed for the same loading conditions but by two different methods; and were tested to failure. Frame USD-1 was designed by the Ultimate Strength Design, while Frame LD-1 by a Limit Design method. The columns were 21-in high while the beam was 84-in long. The loading procedure consisted of proportionately loading the beam and columns up to the design load, and then applying the lateral load to failure. The computer study and the stability model solution showed that frames subjected to low column thrusts remained in stable equilibrium until two plastic hinges form, thus constituting a mechanism. The two experimental frames remained in stable equilibrium until two plastic hinges formed in the beams. The ultimate lateral loads of Frames USD-1 and LD-1 exceeded the design lateral load by 66% and 33%, respectively. Based on this investigation, it appears that Limit Design may be used for low-rise unbraced reinforced concrete structures.

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During the 1970s, the United States passed a series of laws regulating the handling and disposal of hazardous material. The new rules drastically increased the cost of processing toxic wastes. Consequently, many producers began investigating methods that would render toxic material non-hazardous. one solution developed was cement encapsulation, a process that incorporates toxic material into a cement matrix, thus solidifying the waste and reducing the potential for the migration of toxins into the environment. This process can be used to prepare a waste for disposal or can be used to develop a construction material, thus mitigating costs further. This solution was selected by Roanoke Electric Steel as a possible way to dispose of electric arc furnace dust, a by-product which contains a variety of heavy metals which are classified as hazardous by the United States Environmental Protection Agency. In this study, the furnace dust was incorporated into mortar as a portion of the fine aggregate. By including a chelating agent and a stabilizing agent, mortar was developed which meets the requirements of ASTM C150 with respect to strength and time of setting. The optimum mixture has a 28 day strength of 4500 psi and passed the EP Toxicity test, as required by the Environmental Protection Agency before a material can be delisted. To further validate the use of furnace dust in masonry products, the mortar was evaluated for its dimensional stability, both physical and chemical, and for its freezing and thawing durability characteristics. / Master of Science

Master of Science

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: A construction method that proves to be the best today will not necessarily be the best method for application in 20 years. Therefore, with changing circumstances, engineers have to consider all the options before selecting a specific method. Options that are weighed in this study are in-situ concrete construction and hybrid concrete construction. Hybrid concrete construction is the combination of in-situ and precast concrete in structures, with the purpose to exploit the advantages of each to its full potential. This construction method gained popularity in the United States and in Europe due to its distinctive benefits. However, the increase of its application in some countries (including South Africa) has been slow and possible reasons for this are investigated in this study. With the intention of improving the South African construction industry, a model is developed for decision making between hybrid concrete construction and insitu concrete construction. The main purpose of a larger research project is to assist project teams in the decision making between precast concrete and in-situ concrete in building construction projects. This decision making is not based on decision making models with mathematical output, since the decision of a construction method is influenced by many variables that may not all be quantifiable. Consequently, instead of prescribing a decision making method, the relevant information is to be provided for the decision maker. The aim of this study is to identify the relevant parameters and to set a framework for further in depth investigation by subsequent theses. A decision making process in any field normally involves having a list of advantages and disadvantages of the different options. Therefore this study includes the following managerial discussion topics: factors that influence hybrid concrete construction, as well as benefits, barriers and other aspects to consider, structural systems and elements, decision making methods and important factors that will be the basis of the decision making process. Traditionally the most important factors for decision making between construction methods were construction cost and duration, but more recently sustainability is becoming increasingly important. It is the civil duty of all parties involved in a project to foresee that most of the criteria of sustainability are met. Sustainability covers all the aspects of economic, social and environmental impacts. Furthermore quality is identified as an important aspect in the decision making process for a construction method. The comparison of precast and in-situ concrete construction is therefore discussed, considering all the abovementioned criteria and investigating possible quantification methods. This information, together with information from future studies, would then allow the project team to consider each aspect involved in the decision making process. / AFRIKAANSE OPSOMMING: Die beste konstruksiemetode vandag sal nie noodwendig die beste metode oor 20 jaar wees nie. Met veranderende omstandighede, moet ingenieurs altyd al die moontlike opsies oorweeg voordat ‘n spesifieke konstruksiemetode gekies word. Opsies wat in hierdie studie bestudeer word, is in-situ betonkonstruksie en hibriede betonkonstruksie. Hibriede betonkonstruksie is die kombinasie van in-situ en voorafvervaardigde beton elmente in strukture, ten einde die voordele van elke metode ten volle te benut. As gevolg van sy voordele, het hierdie konstruksiemetode al hoe meer gewild geraak in Amerika en Europa. Nietemin is die toename in die gebruik van hierdie metode in sommige lande (insluitend Suid-Afrika) traag en moontlike redes hiervoor word in hierdie studie ondersoek. Met die voorneme om die Suid- Afrikaanse konstruksie-industrie te bevorder, is ‘n model vir besluitneming tussen hibriede betonkonstruksie en in-situ betonkonstruksie ontwikkel. Die hoofdoel van ‘n groter navorsingsprojek is om projekspanne te help met die besluitneming tussen voorafvervaardigde en in-situ beton in konstruksieprojekte vir geboue. Hierdie besluitneming is nie gebaseer op besluitnemingsmodelle wat wiskundige resultate lewer nie, want die keuse van ‘n konstruksiemetode word deur te veel veranderlikes, wat nie altyd kwantifiseerbaar is nie, beïnvloed. Gevolglik word relevante inligting aan die besluitnemer verskaf, eerder as om ‘n gekwantifiseerde besluitnemingsmetode voor te skryf. Die doel van hierdie studie is om relevante aspekte te identifiseer en om ‘n raamwerk te skep vir verdere, in diepte studies van volgende tesisse. ‘n Besluitnemingsproses in enige veld word gewoonlik gebaseer op ‘n lys van voordele en nadele van die verskillende opsies. Daarom sluit hierdie studie die volgende bestuursaspekte in: faktore wat hibriede betonkonstruksie beïnvloed, asook voordele, beperkings en ander aspekte om te oorweeg, strukturele sisteme en –elemente, besluitnemingsmetodes en belangrike faktore wat die basis van die besluitnemingsproses sal wees. Tradisioneel was die belangrikste faktore vir besluitneming tussen konstruksiemetodes die koste en tydsduur daaraan verbonde, maar deesdae word volhoubaarheid al hoe meer belangrik geag. Dit is die plig van alle persone betrokke by ‘n projek om te sorg dat die projek aan so veel as moontlik van die kriteria van volhoubaarheid voldoen. Volhoubaarheid sluit al die aspekte van ekonomiese-, sosiale- en omgewingsimpakte in. Verder is kwaliteit ook geϊdentifiseer as ‘n belangrike aspek in die besluitnemingsproses van ‘n konstruksiemetode. Die vergelyking van voorafvervaardigde- en in-situ betonkonstruksie word dus bespreek met die oog op al die bogenoemde kriteria en, sover moonlik, word die kwantifisering van hierdie aspekte ondersoek. Met hierdie inligting en die inligting van toekomstige studies, kan die projekspan dan elke aspek in die besluitnemingsproses oorweeg.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy