The large ductile deformation response of stiffened plates subjected to blast loads is investigated and simplified methods of analysis of such response are developed. Simplification is derived from modelling stiffened plates as singly symmetric beams or as grillages thereof. These beams are further assumed to behave in a rigid, perfectly plastic manner and to have piecewise linear bending moment-axial force capacity interaction relations, otherwise known as yield curves. A blast loaded, one-way stiffened plate is modelled as a singly symmetric beam comprised of one stiffener and its tributary plating, and subjected to a uniformly distributed line load. For a stiffened plate having edges fully restrained against rotations and translations, both transverse and in-plane, use of the piecewise linear yield curve divides the response of the beam model into two distinct phases: an initial small displacement phase wherein the beam responds as a plastic hinge mechanism, and a final large displacement phase wherein the beam responds as a plastic string. If the line load is restricted to be a blast-type pulse, such response is governed by linear differential equations and so may be solved in closed form. Examples of a one-way stiffened plate subjected to various blast-type pulses demonstrate good agreement between the present rigid-plastic formulation and elastic-plastic beam finite element and finite strip solutions. The response of a one-way stiffened plate is alternatively analysed by approximating it as a sequence of instantaneous mode responses. An instantaneous mode is analogous to a normal mode of linear vibration, but because of system nonlinearity exists for only the instant and deformed configuration considered. The instantaneous mode shapes are determined by an extremum principle which maximizes the rate of change of the stiffened plate's kinetic energy. This approximate rigid-plastic response is not solved in closed form but rather by a semi-analytical time-stepping algorithm. Instantaneous mode solutions compare very well with the closed-form results. The instantaneous mode analysis is extended to the case of two-way stiffened plates, which are modelled by grillages of singly symmetric beams. For two examples of blast loaded two-way stiffened plates, instantaneous mode solutions are compared to results from super finite element analyses. In one of these examples the comparison between analyses is extremely good; in the other, although the magnitudes of displacement response differ between the analyses, the predicted durations and mechanisms of response are in agreement. Incomplete fixity of a stiffened plate's edges is accounted for in the beam and grillage models by way of rigid-plastic links connecting the beams to their rigid supports. Like the beams, these links are assumed to have piecewise linear yield curves, but with reduced bending moment and axial force capacities. The instantaneous mode solution is modified accordingly, and its results again compare well with those of beam finite element analyses. Modifications to the closed-form and instantaneous mode solutions to account for strain rate sensitivity of the panel material are presented. In the closed-form solution, such modification takes the form of an effective dynamic yield stress to be used throughout the rigid-plastic analysis. In the time-stepping instantaneous mode solution, a dynamic yield stress is calculated at each time step and used within that time step only. With these modifications in place, the responses of rate-sensitive one-way stiffened plates predicted by the present analyses once again compare well with finite element and finite strip solutions. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

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As the plastic crisis has emerged as a prominent environmental issue, among others like climate change and biodiversity loss, it has become increasingly important to examine current models of plastic governance. Studying plastic governance provides opportunities to better understand, challenge and hopefully improve upon the landscape of governance within the plastic crisis. For the purposes of this paper, plastic governance is defined as the management and regulation of plastic throughout its life cycle, from production to disposal. The plastic crisis has complex socio-political and ecological dimensions that shape both plastic's problems and potential solutions. Environmental rhetoric surrounding plastic and plastic governance fosters, as well as exemplifies, the dynamic human and ecological dimensions at play in the plastic crisis. For example, the prominence of rhetoric like "Reduce, Reuse and Recycle" and recycling generally demonstrate the creation and reinforcement of waste management and consumer responsibility as the main problems and solutions within plastic governance. Focusing on Canada and the recent announcement of a national ban on single-use plastic, I explore the impacts of environmental rhetoric on the existing and developing governance landscape for plastic. By examining the use of or appeal to environmental rhetoric among state, corporate and civil actors in Canada, I apply concepts from the social science theories of critical political ecology and constructivism in order to gain a deeper understanding of the political and ecological dimensions of the plastic crisis and governance. In particular, I examine the ways in which the coproduction of science and politics informs the characterization of the plastic crisis itself as well as any potential solutions. By studying how rhetoric shapes the problems and solutions we see and emphasize, I will identify and explore norms and gaps within governance throughout plastic’s life cycle. As well, I consider rhetoric surrounding the actors within the plastic crisis and examine how identity and perception play a role in plastic governance. This research allows for deeper critique of plastic policies or initiatives in order to provide potential recommendations for advancing environmental sustainability in Canada.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Waste plastic disposal and excessive use of fossil fuels have caused environment concerns in the world. Both plastics and petroleum derived fuels are hydrocarbons that contain the elements of carbon and hydrogen. The difference between them is that plastic molecules have longer carbon chains than those in LPG, petrol, and diesel fuels. Therefore, it is possible to convert waste plastic into fuels. The main objectives of this study were to understand and optimize the processes of plastic pyrolysis for maximizing the diesel range products, and to design a continuous pyrolysis apparatus as a semi-scale commercial plant. Pyrolysis of polyethylene (PE), polypropylene (PP), and polystyrene (PS) has been investigated both theoretically and experimentally in a lab-scale pyrolysis reactor. The key factors have been investigated and identified. The cracking temperature for PE and PP in the pyrolysis is at 450 ºC, but that of PS is lower, at 320 ºC. High reaction temperature and heating rate can significantly promote the production of light hydrocarbons. Long residence time also favours the yield of the light hydrocarbon products. The effects of other factors like type of reactor, catalyst, pressure and reflux rate have also been investigated in the literature review. From the literature review, the pyrolysis reaction consists of three progressive steps: initiation, propagation, and termination. Initiation reaction cracks the large polymer molecules into free radicals. The free radicals and the molecular species can be further cracked into smaller radicals and molecules during the propagation reactions. β-scission is the dominant reaction in the PE propagation reactions. At last, the radicals will combine together into stable molecules, which are termination reactions. There are three types of cracking of the polymers: random cracking, chain strip cracking, and end chain cracking. The major cracking on the polymer molecular backbone is random cracking. Some cracking occurs at the ends of the molecules or the free radicals, which is end chain cracking. Some polymers have reactive functional side group on their molecular backbones. The functional groups will break off the backbone, which is chain strip cracking. Chain strip cracking is the dominant cracking reaction during polystyrene pyrolysis. The reaction kinetics was investigated in this study. The activation energy and the energy requirement for the pyrolysis are dependent on the reaction process and the distribution of the final products. Following the equations from other literatures, the theoretical energy requirement for pyrolyze 1kg PE is 1.047 MJ. The estimated calorific value of the products is about 43.3 MJ/kg. Therefore, the energy profit is very high for this process. The PE pyrolysis products are mainly 1-alkenes, n-alkanes, and α, ω-dialkenes ranging from C1 to C45+. The 1-alkenes and the n-alkanes were identified with a special method developed in this research. It was found that secondary cracking process has a significant influence on the distribution of the product. This process converts heavy hydrocarbons into gas or light liquid product and significantly reduces 1-alkenes and α, ω-dialkenes. This secondary process can be controlled by adjusting the reflux rate of the primary product. The product of PE pyrolysis with maximized diesel range output consist of 18.3% non-condensable gases, 81.7% w/w liquid product, and less than 1% pure carbon under high reflux rate process. Some zeolite catalysts were tested to reduce the heavy molecular weight wax. It was found that NKC-5 (ZSM-5) was the most effective catalyst among zeolites tested. The proportion of the non-condensable gases was promoted from 17% w/w to 58% w/w by adding 10% w/w NKC-5 into the PE feedstock. The products of PP pyrolysis are mainly methyl- oligomers. The reflux effect on the product from pyrolysis of PP is not as great as that on PE. The PP pyrolysis product with high reflux rate consists of 15.7% non-condensable gases, 84.2% condensed liquid product, and less than 0.25% char. Cyclohexane is the dominant component, 21%w/w in the liquid product. 44%v/v of the non-condensable gases is propene. In the pyrolysis product of PS, there are 4% non-condensable gases, 93% liquid, and 3% char. Styrene accounts for 68.59%w/w in the PS liquid pyrolysis products due to the chain strip reactions. There was 19% v/v hydrogen in the gas product, which did not exist in the PE pyrolysis gas product. The composition of the char is almost pure carbon, which is similar to that from PE pyrolysis. The mixture of virgin and post-consumer PE, PP and PS have also been investigated to identify the feedstock interaction and the effect of the contamination on the product. The interaction promotes the production of non-condensable gases. However, the effect of the interaction on the distribution of total product is not significant. Contamination of paper labels on the post-consumer plastics may result in higher solid residue in the product but no significant effect on the product was found in this study. Based on the achievements, a continuous semi-scale reactor has been designed and constructed at maximum capacity of 27.11kg/hr in this research. From the experiments of pyrolysis of both virgin PE and post-consumer PE on this semi-scale pyrolysis reactor, it was found that the major components are 1-alkenes, n-alkanes, and α, ω- dialkenes. The distribution of the condensed products of PE pyrolysis from the semiscale reactor is the same as that of the products from low reflux rate process with the lab-scale reactor. However, the proportion of non-condensable gases is much higher than that from pyrolysis in the lab-scale tests with low reflux rate because the semiscale plant has higher reaction temperature and heating rate. Lower proportion of unsaturated hydrocarbons was found in the condensed product from the post-consumer PE pyrolysis than in the virgin PE product because of the contamination on the postconsumer PE. The actual energy consumption for cracking and vaporizing PE into fuels is 1.328 MJ/kg which is less than 3% of the calorific value of the pyrolysis products. Therefore, the pyrolysis technology has very high energy profit, 42.3 MJ/kg PE, and is environmental-friendly. The oil produced has very high quality and close to the commercial petroleum derived liquid fuels. The experience of design and operation of the semi-scale plant will be helpful for building a commercial scale plant in the future.

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The interface failure between caps and natural soil in trenches containing buried low level nuclear waste material was investigated in this study. The Casa Grande Highway Farm (CGHF) soil was used for the entire investigation. This soil is described as being a silty sand with approximately 23% by weight passing sieve No. 200. Other preliminary testing was performed on the same soil. Isotropically consolidated drained (CID) tests were performed on the laboratory compacted samples at different degree of saturation including fully saturated specimens. Suction pressure was measured in the laboratory by adopting pressure plate extractor and compared with determined effective suction in triaxial testing. A generalized failure equation, in term of strength parameters and suction pressure, was defined for all degrees of saturation. The consideration of unsaturated soil sets the current modified model apart from previous bounding surface which only allows use of fully saturated cohesive soil. The saturated material constants associated with the model are identified. These new constants are obtained from a generalized failure equation. The model was then verified by comparing predictions with other laboratory tests which are not used in the calibration. Generally a good agreement between the model and test results was found for stress-strain, stress path and volumetric strain response at different degrees of saturation. Extensive interface tests were performed in the conventional direct shear machine with some modification. Similar to trench cap soil and natural soil in the field, the test specimens were prepared at different degrees of saturation and density (compaction effort). Comparisons were made for the effects of magnitude of normal load, degree of saturation, density, compaction effort, moisture migration and dissimilar bodies density. An interface element and the modified bounding surface model and elasticity model was used in a finite element program to predict the interface response for the laboratory results and actual field problems. Material parameters related to the interface were identified and good predictions were observed for the interface behavior.

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