This thesis presents an investigation of pH-responsive, redox-sensitive poly(MMA-co- MAA) and poly(EA-co-MAA) hollow particles for the repair of load-bearing soft tissues, such as articular cartilage and the intervertebral disc. Hollow particles continue to attract major interest due to their numerous potential applications. The new method for hollow particle preparation presented in this thesis does not require the use of a colloidal template and is well suited for scaling up. Hollow particles were formed using linear poly(MMA-co-MAA) and poly(EA-co-MAA) aliphatic copolymers synthesised using free-radical chain copolymerisation performed in solution. These copolymers were dissolved in dichloromethane using methanol as a cosolvent and emulsified in water. Diffusion of the methanol into the aqueous phase prompts precipitation of the copolymer at the droplet/water interface. The more hydrophobic copolymers containing less MAA showed improved morphology compared to copolymers containing more MAA. Also, poly(EA-co-MAA) hollow particles had a more spherical morphology than poly(MMA-co-MAA) hollow particles with equivalent MAA contents. This was attributed to the lower Tg of the EA structural monomer, which resulted in more flexible particle shells. Unusually, during potentiometric titration of uncrosslinked hollow particles, the pH of the system decreased with increasing neutralisation. This behaviour is thought to be due to the unfolding of copolymer chains, exposing shielded carboxyl groups. The random structure of the copolymers is believed to be necessary for this behaviour. Crosslinked particles became swollen when the pH was increased using buffers. Concentrated dispersions formed self supporting gels, due to steric confinement, at 5 wt.%. The crosslinking process was performed by functionalising with cystamine using carbodiimide chemistry. This introduced disulphide crosslinks; which could be cleaved under reducing conditions at high pH, dissolving the gels. This ability to reduce the hollow particle shells to their constituent linear copolymer chains gives potential for natural removal from the body via extraction by the renal system. pH-triggered loading and release of a hydrophilic dye using crosslinked hollow particles was demonstrated. The similarity of the particle formation process to traditional solvent evaporation also allowed the loading of a hydrophobic dye. However, these particles were not crosslinked so release following swelling could not be investigated. Cystamine-crosslinked systems suffered from degradation due to thiol-disulphide exchange at high pH (~ pH 8). Crosslinking of one system was performed using 2-amino ethyl methacrylate (AEM). This introduced covalent, vinyl intra-shell crosslinking; which did not break down at high pH. Additional AEM was also used to allow inter-particle UVcrosslinking to form doubly crosslinked (DX) hollow-particle hydrogels. These gels did not re-disperse in buffer. To our knowledge, this is the first example of a covalent hydrogel formed from pH-responsive hollow particles. The DX gels offer improved mechanical properties compared to the singly crosslinked, physical gels. Freeze-dried samples of all of the gels produced during this study showed highly porous structures when observed using SEM. The rapid diffusion of FITC-dextran through a sample of DX gel indicates that these pores were interconnected. This is beneficial as it encourages tissue ingrowth, in addition to allowing the rapid diffusion of nutrients, oxygen and cell waste in vivo.

The advancement of the structural steel manufacturing industry has led to the recent emergence of steel members with Elliptical Hollow Sections (EHS) and Semi Elliptical Hollow Sections (SEHS). Although these sections are gaining popularity among architects, the lack of design guidelines specifically tailored towards these sections inhibits their efficient structural use. Within this context, this thesis provides several steps towards the development of such guidelines. A review of the manufacturing process of hot-rolled steel sections is conducted with emphasis on hollow structural sections. The main factors affecting the formation of residual stresses during cooling of the sections are discussed. Lower bound plastic interaction relations for EHS subjected to combinations of axial force, bi-axial bending moments and torsion are then derived. The formulation is based on the lower bound theorem of plasticity and the maximum distortional energy density yield criterion. Its applicability for conducting the cross-sectional interaction check in structural steel design problems is illustrated through a practical example. A simplified and conservative interaction equation is then proposed based on curve fitting of the results of the lower bound solution. Upper bound interaction relations are next developed for EHS subjected to combinations of axial force, bi-axial bending moments, torsion and bimoments. The formulation is based on kinematically admissible strain fields within the context of the upper bound theorem of plasticity. The interaction relations derived successfully capture the effect of confining radial strains present at welded end sections, as well as sections that are free to deform in the radial direction away from end welded sections. An iterative solution technique is developed to solve the resulting highly non-linear system of interaction relations. The effects of residual stresses and initial imperfections on axial compressive resistance of hot-rolled EHS are then incorporated into the lower bound interaction relations. Towards that goal, the thermo-mechanical properties of steel were extracted from the literature. A thermo-mechanical finite element model was developed for prediction of residual stresses in rolled sections. The validity of the model was assessed by comparison against residual stress measurements available in the literature. The model is then applied to predict the residual stresses in hot-rolled EHS. A series of geometric and material nonlinear finite element analyses is conducted on columns of EHS sections. The analyses include predicted residual stresses and initial out-of-straightness imperfections in order to determine the inelastic buckling capacity of EHS members and generate column curves for EHS sections. The column curves are subsequently compared to those based on Canadian, American and European design codes. Two column curve equations are proposed in a format similar to that of the Canadian Standards for buckling about major and minor axes. The column curves were subsequently combined with the interaction relations developed to provide design rules for EHS members under combined loads. The last contribution of the thesis provides a formulation of lower bound interaction relations for SEHS subject to combinations of axial force, bi-axial bending moments and torsion. An iterative scheme for solving the parametric form of the interaction relations is developed and a grid of admissible stress resultant combinations is generated. A series of trial functions are fitted to the grid of internal force combinations and two simplified and conservative interaction equations are proposed.

Stability calculations of prefabricated concrete structures with help of FEM-tools demand knowledge about how the elements are related to each other. This thesis concerns how joints between building elements affect the results when modelling prefabricated concrete structures, with demarcation to joints between hollow core (HC) slabs and between solid wall elements. The thesis also covers how the properties of the floor can be adjusted to account for the effects of the joints without modelling every single element. The work started by measuring the deflection of 10 HC-slabs jointed together and loaded in-plane acting as a deep beam, in a FE-model made with Robot™, from Autodesk®. The joints between the HC-elements were modelled either rigid or elastic, and the cross-section and the length of the HC-elements were varied. The linear elastic stiffness between the HC-elements was obtained from the literature as 0.05 (GN/m)/m. The results showed that a changed cross-section geometry gave greater differences in deformation than a changed length. The in-plane shear modulus was then adjusted for the HC-elements in the rigid cases until the same deflection was achieved as for the elastic cases. The result showed that the shear modulus in average for the different cross-section geometries and lengths had to be reduced with a factor of 0.1 to account for the joints. Based on the geometry of a castellated joint between prefabricated solid concrete walls, a calculation model was developed for its linear elastic stiffness. The result was a stiffness of 1.86 (GN/m)/m. To verify the calculated stiffness, a FE-model was developed consisting of a 30m high wall, loaded horizontally in-plane and with one or two vertical joints where the stiffness was applied. The deflection and the reaction forces were noted and the result from the calculated stiffness was compared to other stiffnesses and assessed reasonable. The reaction forces were shown to depend on the stiffness of the joint. The reduced in-plane shear modulus of the HC-elements and the calculated stiffness of the wall joints were then used in a FE-model of a 10-storey building stabilised by two units. The vertical reaction forces were analysed and the results showed 0.02 % difference in the reaction forces in the stabilising units when consideration of the joints between the HC-elements were taken into account and 0.09 % when the vertical joints in the shear wall were taken into account. The results for the wall joint differed from the results when only the wall was modelled. This was thought to be a result of that the floors counteract the shear deformations in the wall joints. The influence of the floor joints was not significant for the building considered in this thesis, but for buildings with non-continuous configuration of the stiffness in the shear walls the outcome may be another, in these cases the reduction factor may be useful. / Vid stabilitetsberäkningar av prefabricerade betongstommar med hjälp av FEM-verktyg ställs krav på kunskap om hur elementen förhåller sig till varandra. Detta arbete berör hur fogar mellan byggnadselement påverkar modellering av prefabricerade betongstommar med avgränsning till fogar mellan håldäckselement och mellan solida väggelement. Arbetet berör även en studie i hur ett bjälklags egenskaper kan justeras så att fogarnas effekt kan tillvaratas utan att modellera varje enskilt håldäckselement. Arbetet inleddes med att utböjningen analyserades hos 10 st ihopskarvade håldäckselement, lastade i dess plan likt en hög balk, i en FE-modell skapad i programmet Robot™, från Autodesk®. Fogarna mellan håldäcken modellerades som antingen rigida eller elastiska och håldäckens tvärsnittsgeometri och längd varierades under testet. Den linjära styvheten mellan håldäcken togs från litteraturen som 0.05 (GN/m)/m. Resultatet visade att ändrad tvärsnittsgeometri gav större skillnader för deformationen än varierad längd på håldäcken. Håldäckens skjuvmodul justerades sedan i dess plan för de rigida testen tills dess att de uppnådde samma utböjning som de elastiska. Resultatet visade att skjuvmodulen behövdes reduceras med en faktor 0.1, i medeltal för de olika tvärsnittsgeometrierna och håldäckslängderna. Utefter geometrin på en fog med förtagningar mellan prefabricerade väggar togs en beräkningsmodell fram för den linjärelastiska styvheten i väggfogarna. Resultatet blev en styvhet på 1.86 (GN/m)/m. För att verifiera den beräknade styvheten togs en FE-modell fram bestående av en 30m hög vägg lastad horisontellt i dess plan med en eller två vertikala fogar där en linjär styvhet applicerades. Utböjningen samt reaktionskrafterna noterades, resultatet för den uträknade linjära styvheten jämfördes med andra styvheter och bedömdes utifrån detta vara rimlig. Reaktionskrafterna visade sig vara beroende av styvheten på fogen. Den sänkta skjuvmodulen för håldäcken och den beräknade linjära elasticiteten för väggarna användes sedan i en FE-modell av en 10-våningsbyggnad med två stabiliserande enheter där de vertikala reaktionskrafterna analyserades. Resultatet visade att endast 0.02 procentenheter skiljer reaktionskrafterna i de stabiliserande enheterna då hänsyn tas till fogarna mellan håldäcken och 0.09 procentenheter då hänsyn tas till fogarna mellan väggarna. Resultatet skiljer sig från när endast väggen modellerades, vilket tros bero på att bjälklaget hjälper till att motverka deformationer i väggfogarna. Fogen mellan bjälklagselementen tros kunna ha större inverkan på en byggnad med stabiliserande enheter som drastiskt ändrar styvhet från ett plan till ett annat, i dessa fall kan den framtagna reduktionsfaktorn vara av nytta.

No description available.

The area around a plant’s roots hosts a complex and diverse microbial community. This environment can include a large number of bacteria that live on the surface of the root and benefit from the nutrients that the roots exude into the soil. These microbes can in turn be beneficial to the plant by protecting the roots from harmful fungi or stressful environmental conditions such as drought. In this thesis, several root-mimetic systems (RMSs) were developed for the study and growth of plant-beneficial bacteria in the laboratory environment. The RMS uses a porous hollow fiber used in hemodialysis as a surface for microbial growth. This fiber can either be draped into liquid nutrients or nutrients can be pumped through the hollow fiber with seepage through pores in the fiber to the outside. These systems are simple but well-controlled models of how a root would feed a bacterial community. The RMSs can be used to study how bacteria receiving nutrients through the RMS react to external factors, and if the bacterial response varies with nutrients received through the fiber. One such application is to study how plant colonizing microbes react to stressors like nanoparticle technology, a growing part of the fertilizer industry. Several different commercial hollow fiber membranes were explored as possible surfaces for microbe attachment. A synthetic polysulfone / polyvinylpyrrolidone hollow fiber membrane, treated with bleach to change the surface properties, was found to be a favorable surface for attachment of the beneficial root-colonizing microbe Pseudomonas chlororaphis O6 (PcO6). In addition to hollow fiber membrane chemistry, the nutrient composition delivered to the bacteria strongly influenced surface colonization and biofilm formation. Thus, using the hollow fiber root model, bacteria can be studied with respect to their responses to changes in nutrient composition as well as their response to stressors such as nanoparticles. Contrasted with studying bacteria on a living root, the model systems developed in this thesis allow microbes to be investigated without the added complexity of unknown variations in the nutrients that the roots pump into the soil.

A series of tests was performed to consider the behaviour of short composite columns under axial compressive loading, covering a range of S275 and S355 grade steel square hollow section filled with normal and high strength concrete. The interaction between the steel and the concrete component is considered and the results show that concrete shrinkage has an effect on the axial strength of the column. Comparisons between Eurocode 4, ACI-318 and the Australian Standards with the findings of this research were made. Result showed the equation used by the ACI-318 and the proposed Australian Standards gave better predication for the axial capacity of concrete filled SHS columns than the Eurocode 4.

No / In composite steel beams with precast hollow core slabs, the amount of transverse reinforcement can have a significant effect on the shear and slip capacity of the mechanical shear connectors. The issue of connector ductility becomes especially important when partial shear connection is adopted, as premature failure of the shear connectors would lead to sudden failure of the composite beam. This chapter presents its findings on the effect of transverse reinforcement on connector ductility and proposes design equations. Transverse reinforcement is used to provide ties for the slabs and confined concrete from splitting. The ductility of the shear connector, that is, slip capacity is directly affected by the amount of transverse reinforcement. Design equations presented in this chapter for estimating the shear capacity of the headed shear stud show a good correlation with the push-off test results. For full shear connection design, pre-splitting shear capacity of the headed stud can be used for the composite design, while for partial shear connection design, post-splitting shear capacity of the headed stud should be used. In general, a minimum transverse reinforcement of T16 bars should be used if partial shear connection design is used to ensure a minimum ductility of 6mm slip.

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No / This paper described the finite element modelling of the semi-rigid composite beam-column joints with the composite steel beams and precast hollowcore slabs which can accurately simulate the moment-rotation response of the connections. Using the general purpose finite element software ABAQUS, a three dimensional model of the composite joint is set up. The techniques of simulating the bolt force, the endplate, the concrete elements, the reinforcement, the shear connectors and the interaction between the slabs and the steel beams are discussed. The results are presented and compared with the experimental data and good agreement is obtained. Parametric studies using the developed model will be performed to gain better understanding of this form of composite joints.

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