<p> The thesis summarizes the experimental and analytical results of studies on the behavior of two FRP-encased steel-concrete composite columns under axial loading. Composite columns have been conventionally constructed using steel and concrete. This study utilizes FRP in combination with steel and concrete to manufacture composite columns with enhanced behavior. The first type of column is a concrete-encased steel column wrapped with epoxy-saturated glass and carbon fiber reinforced polymer (GFRP and CFRP) sheets in the transverse direction. The second type of composite column utilizes a GFRP tube that surrounds a steel I section column, which is subsequently filled with concrete. </p> <p> To the best of the author's knowledge, columns comprising FRP, steel and concrete in the shape of the proposed composite systems has not been reported on in the literature. This study includes two major phases. In the first phase, behavior of stub columns is investigated where stability effects are ignored and failure is governed by the loss of cross-sectional strength. In the second phase, influence of stability on the behavior of the proposed composite columns is studied by testing specimens with various slenderness ratios. </p> <p> To investigate the cross-sectional strength, a total of nine short (500 mm in height) composite column specimens were constructed and tested under axial compression. Five specimens were wrapped with FRP sheets and the remaining four were constructed using a GFRP tube. Experimental results showed significant enhancement in the behavior of the composite columns which was achieved due to confinement and composite action between the constituent materials. The compressive strength of the confined concrete core in the composite specimens constructed using FRP sheets and GFRP tube increased by a factor of 2.4 and 1.8, respectively. An analytical model was developed to predict crosssectional behavior of the proposed composited column. </p> <p> With the primary objective of investigating the influence of slenderness on the behavior of the composite columns, ten additional column specimens, ranging between 1,000 mm and 3,000 mm in height, were tested. Five specimens were constructed using FRP sheets and five constructed using the GFRP tube technique. It was found that the compressive strength of the confined concrete core in the longest tubular composite specimen was reduced to approximately 60% of that of the corresponding short specimen. No confinement was achieved in the longest FRP wrapped composite column specimen. </p> <p> Three bare steel columns, ranging between 500 mm and 3,000 mm in height, were also tested to facilitate comparison with the composite columns in terms of increased axial capacity, as well as stiffness and energy dissipation characteristics of the columns. The compressive strength, elastic axial stiffness and ultimate axial strain of the bare steel columns increased by a factor of up to 10, 6 and 3, respectively, in the composite columns constructed utilizing the concrete-filled GFRP tube. These factors were reduced to 5 .2, 2.5 and 2.6, respectively, in the concrete-encased steel columns wrapped with FRP jackets. </p> <p> Finally, an analytical model was developed to establish the capacity curves for the proposed composite columns accounting for slenderness effects. A simple design equation to predict the compressive strength of the tubular composite columns was proposed based on the capacity curve generated from the analytical model. Compressive capacity of the composite columns predicted using the proposed design equation showed favorable agreement with the experimental results. </p> / Thesis / Doctor of Philosophy (PhD)

No / Closed-form expressions for the small axial deflection and stress distribution of axially loaded rubber blocks of elliptical cross-section, whose ends are bonded to rigid plates, are derived using a superposition approach. The governing equations and conditions are satisfied exactly, based upon the classical theory of elasticity. Easily calculable expressions are derived for the corresponding apparent Young¿s modulus and the modified apparent Young¿s modulus in forms analogous to those previously given for blocks of circular cross-section.

Stay-in-place (SIP) formwork has been used as an alternative to the conventional formwork system. The systems are mainly assembled on site, hence simplifying the construction process and reducing the construction time as the removal procedure has been eliminated. SIP formwork systems can be divided into two main categories; structural and non-structural formwork, based on their contribution to resist applied loads. The structural formwork provides the same advantages as the non-structural formwork, in addition to its contribution to resist the applied loads. As a result, the cross section and the reinforcement of the structural member can be reduced. Recently, polyvinyl chloride (PVC) has been used as a stay-in-place formwork because of its lower cost compared to other materials, durability, and ease to assemble. The PVC SIP formwork consists of interconnected elements; panels and connectors that serve as permanent formwork for the concrete walls. In this study, the behaviour of the PVC encased reinforced concrete walls under eccentric compression loading was investigated. The variables in this study were the type of the specimen (PVC encased or control), the longitudinal reinforcement (4-10M or 4-15M rebars) and the eccentricity of the applied compression load (33.87 mm, 67.73 mm and 101.6 mm). Generally, the control walls (without PVC encasement) failed by yielding of the steel followed by crushing of the concrete, or by crushing of the concrete without yielding of the steel. For the PVC encased walls, buckling of the PVC occurred after the concrete crushed. The PVC encased specimens showed a higher peak load than their peer control walls. The effect of the PVC on increasing the ultimate capacity at a given eccentricity was more significant for the walls reinforced with 4-10M than the walls reinforced with 4-15M. For the lowest reinforcement ratio (4-10M), the PVC encased specimens showed an increase in peak load by 37.2% and 17.1% at an eccentricity of 67.73 mm and 101.6 mm, respectively. When the reinforcement was increased to 4-15 M, the increase in the peak load dropped at all eccentricities to 10%. For the vertical and the mid-span deflection, the PVC encased specimens and the control specimens showed the same values. Also, the test results showed an increase in the energy absorption capacity for the PVC encased specimens compared to the controls specimens, where the effect for the walls reinforced with 4-10M was higher than the walls reinforced with 4-15M at a given eccentricity. An analytical model was developed to predict the ultimate load capacity of the specimens taking into consideration the effect of the PVC on the load carrying capacity of the walls. The provision was derived based on the moment magnification factor method in which the effect of secondary stresses associated with the column deformations was taken into consideration. The calculated capacities of the PVC encased specimens showed a conservative error of 5.9% on average.

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No description available.

Carbon-fibre reinforced polymer (CFRP) laminates are widely used in various engineering applications, such as in race cars and aircrafts, because they are light, stiff and strong. They commonly contain stress raisers in the form of holes and notches (for mechanical joining methods, routing of pipes and cables etc.) and are also often subjected to complex combined multi-axial stress conditions during service. Yet their notched multi-axial fracture behaviour remains largely unexplored. This is the main contribution of the thesis. First, a novel loading fixture for applying a wide range of in-plane loading modes is developed based on the popular Arcan’s method. Termed the ‘modified Arcan rig’, it utilises friction gripping to transfer loads into tabbed specimens. This loading fixture is used to test centre-notched multi-directional CFRP laminates under different combinations of tension and shear stresses. Together with penetrant-enhanced X-ray CT and laminate de-ply, the fracture behaviour of quasi-isotropic CFRP specimens is investigated for the following loading modes: pure tension, pure compression, in-plane shear, and combined tension and shear. Two notch geometries (sharp notch and circular hole) are investigated to allow for an assessment of the role of stress concentration upon strength and damage development to be performed. Three distinct fracture modes are observed in a tensile/compressive-shear stress space (termed Mechanism A, Mechanism B and Mechanism C). It is observed that quasi-isotropic specimens with a central sharp notch are consistently stronger than equivalent specimens with a central circular hole (for all stress states investigated). An underlying micromechanical explanation concerning the effects of damage upon strength is proposed. Second, a finite element (FE) model is developed using the commercial FE program, Abaqus FEA to simulate the observed progressive damage and failure in the quasi-isotropic specimens. The FE model employs independent material property data as inputs. Overall, good correlation between the simulations and the experiments is obtained, validating the FE strategy. The capabilities of the model are extended to predict the notched fracture behaviour of the specimens under combined compression and shear loading, for which experimental work has not been done by the author, but for which literature data exists. Finally, the effect of laminate lay-up upon the notched multi-axial fracture behaviour of the CFRP specimens is explored by considering a 0° ply-dominated lay-up, a ±45° ply-dominated lay-up and a cross-ply lay-up, alongside the quasi-isotropic lay-up. Experiments reveal that all lay-ups exhibit Mechanisms A, B and C. However, the extent of damage in each Mechanism as well as the regime in which each Mechanism operates in (in the failure envelopes) strongly depend on the lay-up of the specimen. As expected, the tensile strengths and compressive strengths increase with the proportion of 0° plies. Surprisingly, the shear strengths do not scale with the proportion of ±45° plies; the specimen geometry and material orthotropy are attributed as reasons for this. In contrast to the case of the quasi-isotropic lay-up, the extent of subcritical damage induced by the circular hole is not always lower than that induced by the sharp notch for the other lay-ups. The difference in the extent of damage between both notch geometries is reflected in the notched strengths of the lay-up in question. These experimental observations are adequately predicted by the FE strategy, which further validates it as a reliable predictive tool for composite fracture.

Dans le cadre du Projet National SOLCYP, le présent travail avait pour but d'étudier la réponse des pieux sous chargements axiaux pour les phases avant, pendant et après cycles. Pour atteindre cet objectif, une étude expérimentale étendue a donc été réalisée par le moyen de deux compagnes d'essais de chargements cycliques sur différents types de pieux instrumentées (battus, forés, vissés) dans deux sites expérimentaux : le site de Merville dans l'argile surconsolidée des Flandres et le site de Loon-Plage près de Dunkerque dans les sables denses des Flandres. Les essais cycliques comportaient des essais en compression, en traction et alternés avec des séries de cycles à forte amplitude conduisant à la rupture cyclique et des séries d'amplitude modérée à très grands nombres de cycles (N>5 000 cycles).L'interprétation de ces essais a englobé, d'une part, une analyse globale du comportement des pieux sous chargements cycliques notamment (i) la réduction de la capacité du pieu; (ii) le nombre de cycles que le pieu peut support avant la rupture (iii) l'évolution du déplacement en tête des pieux (rigidité cyclique). D'autre part, elle a intégré une étude locale en particulier sur la dégradation du frottement latéral et l'évolution de la résistance de pointe du pieu. Cette thèse, basée sur l'étude expérimentale, a permis la formulation des conclusions pratiques sur le comportement des pieux sous chargements cycliques axiaux et a proposé des perspectives pour bien cerner cette problématique / As part of the French National research project SOLCYP, the purpose of this work was study the behavior of the piles under axial loadings for the phases before, during and after cycles.To achieve this objective, an extensive series of static and cyclic axial pile load tests have been carried out in two experimental sites of the North of France: the overconsolidated Flandrian clays (Merville experimental site) and in dense Flandrian sands (Loon-Plage experimental site). Tests were performed on driven closed-ended pipe piles, bored piles and screwed. All piles were instrumented with retrievable extensometers for measuring the load distribution along the pile wall.Cyclic load tests were composed of series of cycles of constant load amplitude. A large range of load histories were applied including series of small amplitude cycles and great number of cycles (N > 5000) and series of large amplitude cycles leading to cyclic failure after a small number of cycles..A large volume of data has been interpreted to describe the effects of axial cyclic loads on the behavior of the piles. The interpretation of these tests included, on the one hand, a global analysis focusing on (i) the potential reduction on the ultimate axial capacity; (ii) the number of load cycles of a given load that the pile can sustain before cyclic failure and (iii) the evolution of displacements of the pile head during cyclic loading (pile stiffness). In addition, it integrated a local study in particular on shaft friction degradation along the pile wall and evolution of the resistance of point of the pile.This thesis, based on the experimental study, allowed the formulation of the practical conclusions on the behavior of the piles under axial cyclic loadings and proposed prospects for determining these problems well

The loads applied to pile foundations installed offshore vary greatly from those encountered onshore, with more substantial lateral and torsional loads. For combined axial and lateral loading the current design practice involves applying an axial load to a deep foundation and assessing the pile behaviour and then considering a lateral load separately. For the problem of an altering directions of lateral loads (e.g. due to changes in the wind directions acting on offshore wind turbines) a clear design procedure is not available. There is thus a need for a clearly established methodology to effectively introduce the interaction between the four different loading directions (two lateral, one axial and one torsional). In this thesis, a model is presented that introduces a series of Winkler elasto-plastic elements coupled between the different directions via local interaction yield surfaces along the pile. The energy based method that is used allows the soil-pile system to be defined explicitly using two equations: the energy potential and the dissipation potential. One of the most interesting applications of this model is to piles subjected to a change in lateral loading direction, where the loading history can significantly influence the pile behaviour. This effect was verified by a series of experimental tests, undertaken using the Geotechnical Centrifuge at UWA. The same theory was then applied to cyclic loading in two dimensions, leading to some very useful conclusions regarding shakedown behaviour. A theoretically based relationship was applied to the local yielding behaviour for a pile subjected to a combination of lateral and axial loading, allowing predictions to be made of the influence of load inclination on the pile behaviour. The ability of this model to represent interaction between four degrees of freedom allows a more realistic approach to be taken to this problem than that considered in current design practice.