Reproduction de : Thèse de doctorat : Sciences appliquées : Metz : 1989. / 1989METZ011S.

Reproduction de : Thèse de doctorat : Biologie cellulaire et moléculaire : Lyon 1 : 2004. / Titre provenant de l'écran titre. 256 réf. bibliogr.

Reproduction de : Thèse de doctorat : Physiologie : Lyon 1 : 2005. / Titre provenant de l'écran titre. 428 réf. bibliogr.

Thèse doctorat : Génie Civil : Villeurbanne, INSA : 2005. / 2e complément de titre d'après folio administratif car différent sur la page de titre. Titre provenant de l'écran-titre. Bibliogr. p. 136-142.

In prestressed precast segmental concrete bridges, conventional longitudinal reinforcement serves only as shrinkage crack controllers. The presence of this reinforcement, however, has restricted the ability to reduce the cross-section of the segments when high strength concrete is used because of the minimum dimensions required to accomodate the reinforcement. Research on fibre reinforced concrete (FRC) indicated that the addition of steel fibres to concrete significantly improved the tensile behaviour and the crack control characteristics of the concrete. This research investigates the feasibility of fibres to replace the conventional shrinkage reinforcement, allowing for the design of thinner and lighter structures with comparable or better crack control characteristics. Extensive work was conducted to investigate the effectiveness of hooked-end steel fibres to control cracks. Seven types of material tests were performed: uniaxial tension test, cylinder compression test, modulus of rupture test, splitting test, free and autogenous shrinkage test, and restrained shrinkage test. In addition, ten 890×890×70 mm concrete panels were tested under in-plane pure-shear loading using the Panel Element Tester. The parameters of study were the fibre volume content (0.5%, 1.0%, and 1.5%), the concrete compressive strength (50 and 80 MPa), and the fibre geometry and tensile strength. In addition to the experimental study, a model was developed to investigate the behaviour of a 1D restrained FRC member subjected to shrinkage. The experimental results indicated that the addition of fibres significantly improved the behaviour of the concrete, particularly the crack control characteristics, the post-peak compressive response, the post-cracking tensile response, the toughness, and the ductility of the concrete. The results also indicated that steel fibres were as effective as conventional reinforcement in controlling shrinkage cracking, provided that sufficient fibre volume content was added to the concrete. For example, in order to achieve a maximum crack width of 0.35 mm, a minimum fibre content of 0.9% and 1.1% should be provided for 50 MPa FRC containing high aspect ratio fibres and low aspect ratio fibres, respectively. In addition, the results indicated the importance of fibre content and fibre aspect ratio on the effectiveness of fibre reinforcement.

In prestressed precast segmental concrete bridges, conventional longitudinal reinforcement serves only as shrinkage crack controllers. The presence of this reinforcement, however, has restricted the ability to reduce the cross-section of the segments when high strength concrete is used because of the minimum dimensions required to accomodate the reinforcement. Research on fibre reinforced concrete (FRC) indicated that the addition of steel fibres to concrete significantly improved the tensile behaviour and the crack control characteristics of the concrete. This research investigates the feasibility of fibres to replace the conventional shrinkage reinforcement, allowing for the design of thinner and lighter structures with comparable or better crack control characteristics. Extensive work was conducted to investigate the effectiveness of hooked-end steel fibres to control cracks. Seven types of material tests were performed: uniaxial tension test, cylinder compression test, modulus of rupture test, splitting test, free and autogenous shrinkage test, and restrained shrinkage test. In addition, ten 890×890×70 mm concrete panels were tested under in-plane pure-shear loading using the Panel Element Tester. The parameters of study were the fibre volume content (0.5%, 1.0%, and 1.5%), the concrete compressive strength (50 and 80 MPa), and the fibre geometry and tensile strength. In addition to the experimental study, a model was developed to investigate the behaviour of a 1D restrained FRC member subjected to shrinkage. The experimental results indicated that the addition of fibres significantly improved the behaviour of the concrete, particularly the crack control characteristics, the post-peak compressive response, the post-cracking tensile response, the toughness, and the ductility of the concrete. The results also indicated that steel fibres were as effective as conventional reinforcement in controlling shrinkage cracking, provided that sufficient fibre volume content was added to the concrete. For example, in order to achieve a maximum crack width of 0.35 mm, a minimum fibre content of 0.9% and 1.1% should be provided for 50 MPa FRC containing high aspect ratio fibres and low aspect ratio fibres, respectively. In addition, the results indicated the importance of fibre content and fibre aspect ratio on the effectiveness of fibre reinforcement.

The purpose of this research was to determine uni-axial response of synthetic fibres required for structural design. The stress versus crack opening curves, required by RILEM for structural design of fibre reinforced concrete, were determined for each fibre type investigate and were used to compare the per fibre post-crack response, the pullout curves, and the flexural response. A study of the fibre distribution was conducted in order to determine the orientation factor required to predict the number of fibres expect in the tensile specimen crack face. The orientation factor, dosage, fibre geometry, and per fibre post-crack response were determined in order to predict the resulting tensile strength of a concrete mix. The tensile strength was compared to that of steel fibre currently being used in structural applications. The synthetic fibres tested only achieve a small percentage of their ultimate tensile strength; in order to produce synthetic fibres for structural applications, the bond strengths must be improved.

Accurate and reliable measurement of meat quality is essential for the Australian beef industry to remain competitive in both the domestic and export markets. Recent developments of the resonator technique have lead to the commercial availability of the High Resolution Ultrasound Spectroscope (HR-US). This research project was designed to assess the potential of HR-US for the analysis of post-mortem bovine muscle. This was accomplished by; 1) establishing a suitable measurement protocol that considered sources of variability, 2) the effects of post-mortem aging on HR-US parameters, 3) analysis of thermal related changes that occur in muscle, and extracted connective tissue during heating, and 4) the use of HR-US for the measurement of the intramuscular fat. A procedure for the measurement of bovine muscle with HR-US was established. Briefly, an external semisolid cell was used as the measurement cell. The frequency range of 2000 KHz to 3000 KHz was selected as the most suitable for whole muscle analysis and all five resonance peaks within this range were analysed and used to obtain velocity and attenuation values of the meat sample. Water was used as the reference media, and measurements were conducted at 250C. Changes were made to this method during experimental work depending on the sample being run and the objectives of the study. The measurement protocol was shown to be repeatable. Factors likely to cause variation in measurements of the samples, such as water loss and freeze-thaw, were also considered when developing the operational parameters of the study. High resolution ultrasound spectroscopy was applied to measure the post-mortem changes that occur in bovine muscle. Using two muscle types, Semitendinosus and Psoas major, significant changes were observed in HR-US parameters with ageing. Significant increases in the acoustic impedance of bovine muscle with increased ageing time were attributed to degradation of the muscle structure. This was confirmed in transmission electron microscopy images where clear disruption the myofibillar structure was apparent in the muscle at 21 days post-mortem.In localised regions the Z bands and the adjoining actin fibres were totally degraded. Water loss from the muscle system had a significant influence on HR-US measurements. Thermal related changes that occur in whole bovine muscle and in isolated intramuscular connective tissue were observed with HR-US. Heat induced changes were identified in whole muscles and included the melting of the fat within samples at 48oC, coagulation of sarcoplasmic proteins between 450C and 55oC, and the shrinkage of collagen fibres at 630C. An 80% reduction in the attenuating properties of extracted connective ageing in buffer solution was observed within the first 5 days. This is attributed to the degradation of proteoglycans and the resulting disassociation of collagen fibrils. Structural changes occurring in extracted connective tissue were observed with TEM. HR-US measurements proved to be highly sensitive to identifying temperatures at which transitions occurred. Unfolding of the triple helix structure of collagen was identified in velocity transitions between 59°C and 63oC. HR-US results suggested a greater sensitivity to thermal related changes in extracted intramuscular connective tissue when compared with differential scanning calorimeter results. An increase in temperature was observed for thermal denaturation of collagen with ageing, however a reduction was also observed in the temperature range at which the denaturation process occurred. Temperature ramps conducted on extracted intramuscular bovine showed a reduction in velocity from 1613.1m/s at 250C to 1343.1 m/s at 900C equalling an overall reduction in velocity of 270m/s. A transition in the velocity trend seen at 46°C indicates the majority of the triglycerides are melted (or in liquid state) above this temperature. Results are confirmed with differential scanning calorimeter thermogram. HR-US measurements showed high sensitivity to increasing concentration of bovine fat in prepared emulsions with an adjusted R2 99.46% for velocity measurements taken at 5100 kHz. Attenuation values at 8100 kHz also showed a strong linear response to increasing fat concentration in the emulsion (R2 98.77). The use of HR-US for the measurement of intramuscular bovine fat demonstrated a high sensitivity to extracted bovine fat in prepared emulsions. An increase in the intramuscular fat content of whole bovine muscles resulted in a reduction in the velocity measurements and an increase in the attenuation of the ultrasonic signal. This provides the basis for potential method for the prediction intramuscular fat in bovine muscle. The present studies have highlighted the complexities of investigations relating to meat quality and have demonstrated the diversity of data required to assess quality. Only when comprehensive data are available, can we hope to accurately determine meat quality and predict how it will vary with changes in animal production and meat processing.

Diss. (sammanfattning) Umeå : Umeå universitet, 2007. / Härtill 5 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2004. / Härtill 4 uppsatser.