Applying lateral confinement to concrete columns using fibre-reinforced polymer (FRP) composites is a very promising technique. FRP rupture is the typical failure mode of FRP wrapped columns under axial compression. numerous experiments have shown that the FRP rupture strain in an FRP wrapped circular column is significantly lower than the FRP ultimate rupture strain determined from flat coupon test of FRP. Despite a large number of studies on the application of FRP confined columns, the mechanisms and level of lower-than-apparent FRP rupture strain still remain unclear. This thesis presents theoretical, Numerical and experimental studies aiming at developing a deeper understanding of the fundamental mechanisms of this phenomenon. A comprehensive literature review was presented providing the background on FRP confined columns, material properties of FRP composites as well as some factors which may lead to premature FRP rupture. A FE analysis was conducted to investigate the FRP hoop strains in the split-disk test, explaining for the first time that the fundamental mechanism of the lower FRP rupture strain in the split-disk test than in the flat coupon test is because strain localisation due to geometric discontinuities at the ends of the FRP and bending of the FRP ring at the gap due to change of curvature caused by the relative moment of the two half disks, as the FRP (as a brittle material) ruptures once the maximum strain at one of these locations reaches the FRP rupture strain. A list of contributory factors affecting the apparent FRP rupture strain in FRP wrapped columns were next identified and classified. An analytical solution was developed to investigate the influence of the triaxial stress state on the FRP strain efficiency, this factor has been shown to have a potentially significant effect on the failure of the FRP wrap but considerable discrepancies exist between predictions using different failure criteria so further research has been identified in this area. FE models were developed to examine the effect of the geometrical discontinuities on the strain efficiency of FRP jackets in FRP wrapped concrete-filled circular steel tubes and FRP wrapped concrete columns. It is demonstrated that severe FRP hoop strain concentrations occur in very small zones near the ends of the FRP wrap in both types of FRP wrapped columns, leading to premature FRP rupture and thus lower strain efficiency. The combined effects of end constraint and FRP overlap on the behaviour of FRP wrapped concrete columns was investigated using a three dimensional FE model considering one half of the length of an FRP-wrapped concrete cylinder. The results have shown that the frication between both ends of a column and the loading platens provides constraints to the ends of the column, but this constraint has little effect on the strain concentration caused by the geometrical discontinuities of the FRP overlap, though the ultimate axial strain of the FRP wrapped columns can be significantly overestimated if the end constraints are not considered.

Steel silos are widely used as long-term or short-term containers for the storage of granular solids, of which a huge range are stored, from flour to iron ore pellets, coals, cement, crushed rocks, plastic pellets, chemical materials, sand, and concrete aggregates. The radius to thickness ratio for silos is in the range of 200 to 3000, so they fall into the category of thin shells, for which failure by buckling is the main concern and requires special attention in design. The primary aim of this thesis is to investigate the possible application of Fibre Reinforced Polymer (FRP) as a new repair and strengthening technique to increase the buckling capacity of thin metallic cylindrical shells. Extensive research has been conducted on the use of fibre reinforced polymer (FRP) composites to strengthen concrete, masonry and timber structures as well as metallic beams. However, all these studies were concerned with failure of the structure by material breakdown, rather than stability. As a result, this thesis marks a major departure in the potential exploitation of FRP in civil engineering structures. Many analyses of cylindrical shells are presented in the thesis. These are all focussed on strengthening the shell against different failure modes. Two loading conditions were explored: uniform internal pressure accompanied by axial load near a base boundary, and axial loads with geometric imperfections. For the latter, local imperfections are usually critical, and two categories of imperfection were studied in detail: an inward axisymmetric imperfection and a local dent imperfection. For the first loading condition, which leads to elephant’s foot buckling, an analytical method was used to derive general equations governing the linear elastic behaviour of a cylindrical shell that has been strengthened with FRP subject to internal pressure and axial compression. It was used to identify optimal application of the FRP. All the later studies were conducted using nonlinear finite element analysis (using the ABAQUS program) to obtain extensive predictions of many conditions causing shell buckling and the strengthening effect of well-placed FRP. In all the cases studied in this thesis, it was shown that a small quantity of FRP composite, applied within a small zone, can provide a significant enhancement of the resistance to buckling failure of a thin metal cylinder. These calculations demonstrate that this new technique is of considerable practical value. However, it is clear that not all the relevant questions have been fully answered, so the author poses appropriate questions and makes suggestions for future work.

Fibre reinforced plastics are widely used for energy dissipating parts. Due to their superior strength to density ratio they provide a high performance and are ideal for lightweight design for crashworthiness. For this, it is essential that the mechanical behaviour of fibre reinforced composites can be predicted correctly by simulation. However, due to the complex inner structure, this is still a challenging task, in particular in case of highly nonlinear crash loading. In this work, a new purely virtual method is developed, which derives the complex fibre structure of a filament wound tube by a chain of numerical simulations. Thereby a finite element simulation of the fibre placement, taking into account the occurring physical effects, constitutes the fundamental base. Based on the results of the manufacturing simulation, a 3D fibre architecture is generated and compared to the real existing structure. The fibre structure, combined with an automatic matrix implementation algorithm, subsequently provides a finite element model of the composite on meso-scale. Using micro-scale analysis, effective material properties for the roving structure, based on filament-matrix interaction, are derived. Incorporation of the effective properties in a USER MATERIAL model completes the finite element model generation. The mesoscale model is subsequently used to analyse the filament wound tube in terms of quasi-static and crash loading. Finally, the obtained results are compared to experimental observations.

Damaged cartilage can cause severe pain and restricted mobility, with few long term treatments available. The developing field of tissue engineering offers an alternative to the currently used full joint replacement. Restoring damaged cartilage through tissue engineering would enable an active lifestyle to be recovered and retained, without restrictions to joint mobility. This is increasingly important as the prevalence of osteoarthritis rises. Tissue engineering requires biomaterial scaffolds that mimic the function of the tissue while cells develop, and so the scaffold must provide the appropriate biological, chemical and mechanical stimuli. In this work, methods were developed to enable the design of scaffolds that mimic the microstructure and mechanical properties of articular cartilage. Electrospinning was investigated as a method to mimic the nanoscale collagen fibres within cartilage extracellular matrix. A parametric study was conducted to determine how changes to a gelatin solution affect the mechanical properties of the non-woven fibrous mesh. The solution properties had a clear impact on the morphology of the fibres, but the effect on the mesh mechanical properties was convoluted. The results demonstrated the need for greater understanding of the 3D morphology of electrospun meshes, to establish how these may be altered in order to design scaffolds with desirable mechanical properties. The fracture mechanics of soft materials are complex, and are generally overlooked when designing tissue engineering scaffolds. The complexities have led to a lack of standardised testing, making comparisons between studies impractical. In this work, fracture testing methods were compared, using a viscoelastic polymer to mimic some of the complexities of soft tissue mechanics. Mode III trouser tear tests and mode I pure shear tests were found to provide reliable measurements. Due to the ease of testing small samples, trouser tear testing was concluded to be the most advantageous for determining the fracture resistance of soft tissue engineering scaffolds. Finally, electrospun meshes were combined with hydrogels to create biomimetic scaffolds, which were characterised using tensile and trouser tear fracture tests. Fibre-reinforcement was shown to enhance the mechanical properties of a weak hydrogel, but diminished those of a strong, tough polyacrylamide (PAAm)-alginate hydrogel. The PAAm-alginate hydrogel exhibited mechanical properties close to those of natural articular cartilage, but without the microstructure that would enhance its suitability for use as a cartilage tissue engineering scaffold. An alternative method for reinforcing PAAm-alginate was proposed, which shows promise for producing a biocompatible scaffold that mimics both the mechanics and the microstructure of articular cartilage. Ultimately, this thesis aimed to improve the design of biomimetic scaffolds for cartilage tissue engineering, and advance mechanical characterisation techniques within this field.

This thesis presents an experimental and theoretical study of the material and structural behaviour of a Steel-Fibre reinforced Reactive Powder Concrete (SF-RPC). The experimental program consisted of three phases. Phase 1 involved the development of a design mix for use throughout the remainder of the study. Phase 2 consisted of an in-depth investigation into the material properties of the mix. The final phase of the experimental component was the testing of 16 plain and prestressed SF-RPC beams. Twelve beams were tested under short-term loading to determine their cracking and ultimate moment capacity. The remaining 4 beams were used to investigate the time-dependent flexural behaviour of prestressed SF-RPC slabs. The material properties were measured using a range of short-term tests and included the compressive and flexural behaviour, static chord modulus of elasticity and crack mouth opening. In addition to the short-term tests, investigation into the time-dependent material behaviour was undertaken and included the creep and shrinkage characteristics of the material. The response of the material to various curing conditions was also investigated. The structural behaviour investigated included the short-term flexural moment-curvature response and load-deflection behaviour of beams and slabs along with the crack patterns of both plain and prestressed SF-RPC members. In addition to the investigations into the short-term flexural behaviour, a study into the time-dependent flexural behaviour was also undertaken. There are currently 2 available models for predicting the flexural response of plain and prestressed RPC cross-sections. The analytical phase of this investigation involved an evaluation of these models. Based on the experimental findings and analysis, a modified model was proposed for calculating the short-term flexural behaviour of plain and prestressed SF-RPC beams. The applicability of an age-adjusted effective modulus method for calculating the time-dependent deformations of prestressed SF-RPC slabs under various levels of sustained loads was also evaluated and found to be adequate with minor refinements.

Innovative new flooring systems utilising lightweight fibre reinforced polymer composite materials may have the significant potential to offer both economic and performance benefits for infrastructure asset owners compared to conventional concrete and steel systems. Over recent years, a range of prototype floor systems using fibre reinforced polymer composites have been developed by researchers at the University of Southern Queensland. However before such structural systems can be widely adopted by industries, fundamental understanding of their behaviour must be improved. Such work will allow for the development of new design and analysis procedures which will enable engineers to efficiently and accurately design and analyse such structures. This dissertation presents an investigation into a new two-way fibre reinforced composite floor slab system. The proposed new two-way slab system is, in essence, a sandwich structure with an innovative hollow core made from a castable particulate filled resin system. The key focus of this dissertation is the development of a new analysis tool to analyse the two-way fibre reinforced composite slab and facilitate subsequent parametric studies into slab configurations for concept refinement. The detailed 3D finite element analyses and experimental investigations are performed to verify the new analysis tool, and provide more detailed insight into the structural behaviour of this new two-way fibre reinforced composite slab. Comparisons with detailed 3D FEA and experiments illustrate that the simplified analysis tool is capable of providing sufficient accuracy for the preliminary analysis of a slab structure. Moreover, the 3D finite element analyses agree well with the experiments, and it is concluded that the behavioural responses of the proposed new slab structure can be reliably predicted. The experimental results show that this new slab concept exhibits quite a robust static behaviour and is likely to have a robust fatigue performance.

The large amount of used polypropylene baler twine generated from the agricultural community may provide a low-cost, environmentally friendly source of fibre reinforcement that can be used to improve the properties of concrete. However, the performance of such fibres for the application has not yet been explored. The effectiveness of using small amounts of chopped baler twine to control the restrained plastic shrinkage cracking of portland cement mortar was investigated in this study. To determine the influence of baler twine fibre type, length and volume fraction on their performance, two types of baler twine ( one composed of strands with circular cross section, the other composed of flat band shape strands) in two lengths (19 mm and 38 mm) and three volume fractions (0.05%, 0.1%, and 0.3%) were evaluated. To compare the performance of baler twine fibre with that of other commercially available synthetic fibres, fibrillated polypropylene fibres at equal lengths and volume fractions was investigated.<p>The restrained plastic shrinkage tests were carried out by subjecting the fibre-reinforced mortar specimens, cast on rough substrate bases, to a wind speed of 2.6 m/s, and relative humidity less than 3% at 35 °C for 22 hours. To evaluate the effectiveness of the fibres, the crack numbers were recorded, and the maximum crack width and total crack area on the surface of each specimen were measured using an image analysis technique. Unrestrained plastic shrinkage tests were also conducted in which fibre-reinforced mortar specimens without the substrate bases were tested under the same environmental conditions.<p>Test results indicate that both types of baler twine are capable of controlling restrained plastic shrinkage cracking to some extent, but are not as effective as fibrillated polypropylene. The baler twine composed of band shape strands performed better than the one composed of strands with circular cross section. Compared with plain specimens, the total crack area was reduced by 95.3, 77.5 and 38.7% when 0.3% volume fraction of 38 mm fibrillated polypropylene, band shape baler twine and circular baler twine fibres, respectively, were added. Similar reductions in maximum crack width were observed. Fibre length did not significantly influence cracking behaviour. Free plastic shrinkage was significantly reduced only when long fibre lengths (38 mm) and high volume fractions (0.3%) were used.

The large amount of used polypropylene baler twine generated from the agricultural community may provide a low-cost, environmentally friendly source of fibre reinforcement that can be used to improve the properties of concrete. However, the performance of such fibres for the application has not yet been explored. The effectiveness of using small amounts of chopped baler twine to control the restrained plastic shrinkage cracking of portland cement mortar was investigated in this study. To determine the influence of baler twine fibre type, length and volume fraction on their performance, two types of baler twine ( one composed of strands with circular cross section, the other composed of flat band shape strands) in two lengths (19 mm and 38 mm) and three volume fractions (0.05%, 0.1%, and 0.3%) were evaluated. To compare the performance of baler twine fibre with that of other commercially available synthetic fibres, fibrillated polypropylene fibres at equal lengths and volume fractions was investigated.<p>The restrained plastic shrinkage tests were carried out by subjecting the fibre-reinforced mortar specimens, cast on rough substrate bases, to a wind speed of 2.6 m/s, and relative humidity less than 3% at 35 °C for 22 hours. To evaluate the effectiveness of the fibres, the crack numbers were recorded, and the maximum crack width and total crack area on the surface of each specimen were measured using an image analysis technique. Unrestrained plastic shrinkage tests were also conducted in which fibre-reinforced mortar specimens without the substrate bases were tested under the same environmental conditions.<p>Test results indicate that both types of baler twine are capable of controlling restrained plastic shrinkage cracking to some extent, but are not as effective as fibrillated polypropylene. The baler twine composed of band shape strands performed better than the one composed of strands with circular cross section. Compared with plain specimens, the total crack area was reduced by 95.3, 77.5 and 38.7% when 0.3% volume fraction of 38 mm fibrillated polypropylene, band shape baler twine and circular baler twine fibres, respectively, were added. Similar reductions in maximum crack width were observed. Fibre length did not significantly influence cracking behaviour. Free plastic shrinkage was significantly reduced only when long fibre lengths (38 mm) and high volume fractions (0.3%) were used.

Ο σκοπός αυτής της διπλωματικής εργασίας είναι η σύγκριση της αποτελεσματικότητας της ενίσχυσης, στοιχείων από φέρουσα τοιχοποιία, με μανδύες συνθέτων υλικών, οι οποίοι αποτελούνταν από στρώσεις ανθρακοϋφάσματος, με οργανική ή ανόργανη μήτρα και με τοποθέτηση ράβδων οπλισμού, από ανθρακονήματα, μέσα στους συνεχείς αρμούς της τοιχοποιίας. Αρχικά δίνονται μορφολογικά και γενικά τεχνικά χαρακτηριστικά. Γίνεται μια σύντομη ιστορική ανασκόπηση για την τοιχοποιία και ακολουθεί ο διαχωρισμός της σε βασικές κατηγορίες. Αναφέρονται οι πρώτες ύλες των τεχνητών λιθοσωμάτων και η διαδικασία παραγωγής τους και στη συνέχεια σημειώνονται τα βασικά είδη τους, με τις συνήθεις διαστάσεις και οι τεχνικές προδιαγραφές τους. Γίνεται ακόμα αναφορά στις κατηγορίες και στις ιδιότητες των κονιαμάτων και των επιχρισμάτων που χρησιμοποιούνται. Ακολουθεί μια περίληψη της μηχανικής της τοιχοποιίας. Περιγράφεται η λειτουργία της άοπλης τοιχοποιίας και ο προσδιορισμός της αντοχής της, υπό θλιπτικά, καμπτικά και διατμητικά φορτία, κατά τον Ευρωκώδικα 6 (EC6) και Τάσιο. Περιγράφονται επίσης τα ελαστικά χαρακτηριστικά της τοιχοποιίας και ο τρόπος, με τον οποίο αυτή συμπεριφέρεται υπό οριζόντια πλευρική φόρτιση, ενώ φέρει θλιπτικά φορτία. Στη συνέχεια γίνεται περιγραφή των ενισχύσεων κατασκευών με σύνθετα υλικά. Κατηγοριοποιούνται τα σύνθετα υλικά και δίνονται οι ιδιότητες των συνθέτων ινο-πλισμένων υλικών. Αναφέρονται εν συντομία οι ιδιότητες των υλικών, ινών και ρητινών, που χρησιμοποιούνται συνήθως για την κατασκευή ινοπλισμένων πολυμερών. Ακόμα αναφέρονται τα βασικά συστήματα ενίσχυσης και οι ιδιότητες των συνθέτων υλικών. Ακολουθεί η μικρομηχανική των υλικών αυτών και οι επιπτώσεις, των περιβαλλοντικών συνθηκών, στην ανθεκτικότητά τους. Επίσης, γίνεται μια περιληπτική αναφορά στις τεχνικές ενισχύσεων δομικών στοιχείων με σύνθετα υλικά. Έπεται μια σύντομη αναφορά στις βάσεις σχεδιασμού ενισχύσεων με σύνθετα υλικά. Δίνονται οι καταστατικοί νόμοι των υλικών για οριακή κατάσταση αντοχής, τόσο για πλήρη συνεργασία όσο και για αποκόλληση του συνθέτου υλικού από την κατασκευή, και για οριακή κατάσταση λειτουργικότητας. Επίσης σχολιάζεται και το θέμα της συνάφειας των συνθέτων υλικών με το υπόστρωμα (τοιχοποιία). Ακολούθως περιγράφονται τα υλικά κατασκευής και ενίσχυσης, τα πειραματικά δοκίμια και δίνονται οι μηχανικές τους ιδιότητες. Ακόμα γίνεται περιγραφή των ειδών των δοκιμίων, που δημιουργήθηκαν, της διαδικασίας ενισχύσεώς τους, σύμφωνα με τους τρόπους που είχαν αποφασιστεί, δηλαδή με κατασκευή μανδυών και με τοποθέτηση ράβδων οπλισμού από σύνθετα υλικά. Επίσης περιγράφονται εν συντομία ο μηχανικός εργαστηριακός εξοπλισμός, που χρησιμοποιήθηκε για την εκτέλεση των πειραματικών διαδικασιών. Στην συνέχεια γίνεται αναλυτική προσομοίωση για κάθε είδος δοκιμίου και ενίσχυσης, από όπου εξάγεται και η θεωρητική τιμή της αντοχής τους, και περιγραφή της πειραματική διαδικασίας, που ακολούθησε για τον έλεγχό τους. Ακολούθως, γίνεται σύγκριση μεταξύ των τρόπων ενίσχυσης και αναφορά των σχετικών πλεονεκτημάτων και τα μειονεκτημάτων τους, ανά κατηγορία δοκιμίων. Τέλος, δίνονται τα συμπεράσματα της εργασίας, που συνοπτικά είναι ότι η χρήση α-νόργανης μήτρας για την κατασκευή μανδυών προσφέρει, με σχετική μείωση της αντοχής, μεγαλύτερη παραμορφωσιμότητα και ικανότητα απορρόφησης ενέργειας και ότι η ενίσχυση, με τοποθέτηση ράβδων ανθρακονήματος, μέσα στους συνεχείς αρμούς της τοιχοποιίας, είναι επισφαλής, λόγω της μη ικανοποιητικής συνάφειάς τους με το συνδετικό κονίαμα, αποτελέσματα, τα οποία μπορούν να χρησιμοποιηθούν για την καλύτερη διαστασιολόγηση των ενισχύσεων με σύνθετα υλικά. Επίσης αναφέρονται κάποια θέματα που χρήζουν περαιτέρω μελέτης, όπως η τοποθέτηση των ράβδων ανθρακονημάτων σε άλλες θέσεις και διευθύνσεις, το απαιτούμενο ποσοστό ινών και η πιθανή τροποποίηση των πειραματικών διατάξεων, ώστε να πραγματοποιηθεί ακριβέστερη προσομοίωση των πραγματικών στοιχείων και φορτίσεων, μιας κατασκευής. / The purpose of this study is the comparison between the use of fibre-reinforced polymers (FRP) as strengthening materials for masonry walls with jackets of polymeric matrix (organic and inorganic) using carbon fabrics and strips (into the constant joints of masonry). First of all, is discribed the history of masorny and its categories. Then, are mentioned the first materials for bricks, the procedure for their produce and their sizes. Also, are mentioned the categories of mortar and plaster. Moreover, is discribed the mechanics of masonry according the Eurocode 6(EC6) and the professor Tasios. Furthermore, are reported the categories of composite materials and their qualities. Also, is annotated the connection between the composite materials and the masonry (substratum). Apart from this, are described the materials that were used to form and reinforce elements of masonry wall. Also, are described the types of elements of masonry wall, that were built, the procedure for their reinforcement and the mechanical equipment of the laboratory, where expirements took place. Moreover, are annotated the analytical model for every type of masonry element, from where theoritical values were taken and the experimental procedure. Furthermore, is presenced the comparison between every type of reinforcment and their advantages or disadvantages. Finally, are decribed subjects for future usage and results of this study.

An extensive amount of research has been reported in previous literature on the behaviour of FRP-confined concrete subjected to concentric axial compression. However, data on the behaviour of high strength concrete confined with various types and configurations of FRP systems is still lacking and no consensus exists on the complete response of FRP-confined concrete. In addition, no appropriate design guidelines are currently available. This thesis reports results from an experimental program involving 112 cylindrical concrete specimens, 88 of which were FRP-wrapped and the remaining 24 were control specimens. All the specimens were 152 mm in diameter and 305 mm in length. Test variables included: amount of FRP materials used, strength and stiffness of FRP materials, concrete strength, and the health of concrete at the time of strengthening. Experimental results indicated that a pre-repair load of up to 77% of the unconfined concrete strength had no appreciable effect on the stress-strain response of FRP-confined concrete. With an increase of the unconfined concrete strength, the strength enhancement, energy absorption capacity, ductility factor and work (energy) index at rupture of FRP jackets all decreased remarkably. A positive correlation was found between confined concrete ductility and FRP rupture strain. In addition, a gradual post-peak failure of the specimens, observed previously from FRP-confined concrete columns tested at the University of Toronto, was also observed in some of the current tests -- owing to the high speed data acquisition system. That ductile failure can be attributed to the gradual unzipping failure of FRP jacket, which in turn is related to specimen size. A new constitutive model was developed based on material properties, force equilibrium and strain compatibility. The size effect was taken into account in the model, which is able to accommodate concrete with a wide range of strength (25 MPa to 110 MPa) confined with various types and configurations FRP systems. Design equations from CSA S806-02 and CSA S6-06 provide reasonable and conservative estimates for the FRP-confined concrete strength. To calculate the peak strain for FRP-confined concrete, an equation based on the work by Berthet et al. (2006) is proposed.