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published_or_final_version / abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy

Concerns have been raised over the use of plastic skylights as smoke vents in large single story buildings. The plastic skylights provide natural light to the building. There has been an assumption that these plastic panels will melt and provide smoke and heat venting during a fire. The plastics commonly used in New Zealand, polyvinyl chloride (PVC), polycarbonate, acrylic and glass fibre-reinforced polyester (GRP) have been tested in small scale experiments to further the understanding of the behaviour of the materials at elevated temperatures. The behaviour of particular interest is the effectiveness of the skylight as a vent for hot buoyant gases. Small scale experiments have been conducted to find the mass flow rate of an unobstructed vent. Experiments have then been carried out on samples of the four skylight materials for a range of exposure temperatures and times. The mass flow has been measured for the deformed sample and compared to the unobstructed flow. The results of the small scale experiments have been analysed and an empirical relationship has been developed for the PVC and polycarbonate material. The acrylic behaviour does not provide enough data to include it in the empirical relationship. The GRP failed to melt and was therefore also excluded from the empirical relationship. A model has been developed to demonstrate the use of the empirical relationship. The model compares four cases, the vents always open, the vents always closed, the vents opening at a single value and the area when calculated using the empirical relationship.

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Characterization of stress-deformation behavior of concrete and rocks have been a subject of active research for a long time. Linear elastic, nonlinear (piecewise) linear elastic, elastic-plastic and endochronic models have been proposed and used by various investigators and the literature on the subjects is very wide. A review of various models together with their implementation is numerical (finite element) procedures is presented in Ref. (77). The primary objective of the present study is to develop a generalized constitutive model based on the theory of plasticity. Although such a model can be used for a wide range of materials, in this dissertation its applications to plain concrete and rocks are emphasised. One of the main objectives of this dissertation is to study constitutive behavior of concrete and soapstone under multiaxial load histories by using a truly triaxial or multiaxial testing device. The truly triaxial device is capable of applying a general three-dimensional state of stress. Samples can be tested along any three dimensional stress path. Therefore, constitutive behavior of concrete and soapstone can be studied under all possible states of stress. The conventional, octahedral, proportional loading and circular stress test series are conducted using the truly triaxial cubical device. For meaningful results, samples with consistent initial properties are essential. In order to produce samples with uniform initial properties such as density, equipment and procedures are developed to standardize the sample preparation process. The test data is used to determine the material constants associated with the proposed constitutive model. The model is then verified by back-predicting the stress-strain curves obtained from the laboratory.

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