Évaluation de la performance à long terme de barres d'armature en PRFV soumises à différentes conditions environnementales sous charges de traction soutenues élevées

Abstract : The long-term performance of glass fiber reinforced polymer (GFRP) bars subjected to high sustained loads and aggressive environmental conditions is not entirely clear and very conservative limits are imposed by available FRP design guidelines and codes. A two-phase (Phase I and Phase II) experimental program was designed to address this issue. Phase I included an experimental investigation and statistical approach to assess the long-term performance and to determine a safe creep-rupture strength value for glass fiber-reinforced polymer (GFRP) bars subjected to different types of environmental exposure. The study sample consisted of 160 bars of various sizes (10 mm, 12 mm, and two types of 15 mm) subjected to different levels of environmental conditioning (unconditioned and exposed to an alkaline solution at 23°C and 60°C) and a range of sustained load levels (40% to 90% of the ultimate tensile strength). The test results were analyzed with Weibull statistical analysis to determine the mean and characteristic creep-rupture strengths, and consequently, a safe design value was calculated. Limitations and variations of the strength degradation model for the life-span prediction was assessed. The impact of sustained load on strength reduction was more pronounced than the combined effect of the alkaline solution and high temperature. The GFRP bars with smaller diameters were more susceptible to creep rupture than the larger ones, while the conditioning had more effect on the bars with larger diameters than the smaller ones. In Phase II, a set of experiments was conducted to assess the flexural behavior of concrete beams reinforced with GFRP bars subjected to a high sustained flexural load after 10 years of natural aging. The experimental program consisted of eight rectangular concrete beams measuring 250 × 250 × 2000 mm. All beams were reinforced with sand coated GFRP bars. Four beams were subjected to a high sustained load of up to 40% of the ultimate tensile capacity of their GFRP bars with simultaneous exposure to aggressive natural weathering (temperatures ranging from -25℃ to 35℃) for 10 years. The remaining four were stored in the laboratory and treated as control specimens without any loading. The conditioned beams were tested up to failure in a four-point bending setup. The results were compared in terms of load–displacement behavior, ultimate strength, displacement capacity, failure modes, and cracking pattern. In addition, the microstructure of the GFRP bars was studied to evaluate the physical changes of the bars, and their bond condition with surrounding concrete at different stress levels. The findings indicate a strength deterioration of only 16% for this early generation of GFRP bars under harsh natural conditioning and high sustained loads for 10 years. On the other hand, the bond between the concrete and GFRP bars as well as the glass transition temperature, infrared spectra and interlaminar shear strength of the GFRP bars remained unaffected. Finally, analytical approaches were implemented to predict the load–displacement behavior and crack widths of the tested beams.La performance à long terme des barres en polymère renforcé de fibres de verre (PRFV) soumises à des charges soutenues élevées et à des conditions environnementales agressives n'est pas tout à fait clairement définie et des limites sévères sont imposées par les guides de conception disponibles. Un programme expérimental en deux phases est conçu pour étudier cette question. Dans la phase I, la résistance à la rupture par fluage des barres de PRFV exposées à différentes conditions environnementales est évaluée pour la nouvelle génération de barres. La phase II examine le comportement en flexion de poutres en béton ayant subi un vieillissement naturel et qui ont été renforcées avec la génération précédente de barres de PRFV. La première phase est réalisée en laboratoire et la seconde phase est une étude sur le terrain. La première série d'expériences est réalisée sur 170 barres et englobe une variété de diamètres de barres (10 mm, 12 mm et deux types de 15 mm), de conditionnement environnemental (non conditionné et exposé à une solution alcaline à 23 °C et 60 °C) et de charges soutenues imposées (40 à 90 % de la résistance ultime à la traction des barres). Les résultats des essais ont été analysés à l’aide d’une analyse statistique de Weibull afin de déterminer les résistances moyennes et les résistances caractéristiques de ruptures par fluage et par conséquent, une valeur sûre pour le dimensionnement a été calculée. Les limites et les variations du modèle de dégradation de la résistance pour la prédiction de la durée de vie ont été discutées. En outre, la microstructure des barres de PRFV non rompues a été étudiée pour évaluer les changements physiques des barres. Les résultats de l'étude montrent que le taux de dégradation est prolongé pour des niveaux de charges soutenues plus faibles. L'impact d'une charge soutenue sur la réduction de la résistance est plus prononcé que l'effet couplé d'une solution alcaline et d'une température élevée. Les facteurs de réduction de la rupture par fluage (Cc) prescrits par les codes de conception actuels sont conservateurs pour les barres de PRFV dans cette étude. Un facteur de réduction environnemental égal à 1,0 peut être utilisé avec les limites de rupture par fluage spécifiées par les codes actuels pour les barres de PRFV noyées dans du béton, non en contact avec le sol et non exposées aux intempéries. La deuxième série d'expériences a examiné le comportement en flexion de poutres en béton renforcées par des barres de PRFV et soumises à une charge soutenue élevée de flexion après 10 ans de vieillissement naturel. Le programme expérimental comprenait huit poutres rectangulaires en béton mesurant 250 x 250 x 2000 mm. Toutes les poutres ont été renforcées avec des barres de PRFV revêtues de sable. Quatre poutres ont été soumises à une charge élevée soutenue allant jusqu'à 40 % de la résistance ultime en traction des barres de PRFV, avec une exposition simultanée à un vieillissement naturel agressif (températures allant de - 25℃ à 35℃) pendant 10 ans. Les quatre autres poutres ont été entreposées au laboratoire comme spécimens témoins sans aucune charge. Les poutres conditionnées ont été testées en flexion quatre points jusqu'à la rupture. Les résultats ont été comparés en termes de comportement charge-déplacement, de résistance ultime, de capacité de déplacement, de modes de rupture et de patron de fissuration. De plus, la microstructure des barres de PRFV a été étudiée pour évaluer les changements physiques des barres et leur adhérence avec le béton environnant à différents niveaux de contrainte. Les résultats indiquent une détérioration de la résistance de seulement 16 % pour cette première génération de barres de PRFV, dans des conditions naturelles difficiles et sous des charges élevées soutenues pendant 10 ans. En revanche, l'adhérence entre le béton et les barres de PRFV, ainsi que la température de transition vitreuse, les spectres infrarouges et la résistance au cisaillement interlaminaire des barres de PRFV n'ont pas été affectés. Enfin, des approches analytiques ont été mises en oeuvre pour prédire le comportement charge-déplacement et l’ouverture des fissures des poutres testées

Design a biomimetic disc using geometric features of the claws

This study presents a numerical investigation regarding the stress distribution on the new designed disc harrow using the ANSYS software. A conventional disc, notched disc, and a biomimetic design inspired by the claw of the leatherwing were analyzed in two conventional plowed and unplowed soils and three tillage depths (4, 7 and 10 cm). Stress analysis for all treatments showed that the highest stress was imposed at the disc-stem junction. Meanwhile the highest deformation occurred at the lowest and the most external part of the discs (land line). The results obtained in this study indicated that the maximum stress exerted from tilling soil to discs increases linearly with tillage depth in both plowed and unplowed soils. Given these results, the maximum stress also at the disc-stem junction changed linearly with tillage depth for all of the three geometric shapes. For the conventional examined harrow in unplowed soil at a depth of 10 cm, the highest maximum stress was 484 MPa and the maximum deformation was 1.84 mm. Using the new geometry for discs in plowed soil, the highest maximum stress and the maximum disc deformation were obtained equal to 130 MPa and 0.92 mm at the same tillage condition, respectively. For all treatments in plowed or unplowed soil, the lowest stress occurred with the biomimetic harrow. The soil- disc interaction stresses exerted on the notched harrow was lower than the conventional disc

Precise Model for Small-Body Thermal Radiation Pressure Acting on Spacecraft

A precise representation of small-body surface thermal radiation pressure effects acting on orbiting spacecraft is discussed. The proposed framework takes advantage of a general Fourier series expansion to compute small-body surface thermal radiation pressure. Fourier series expansion has been used before for the precise representation of solar radiation pressure effects on spacecraft orbiting small bodies. This framework takes into account the geometric relationship of orbiting spacecraft with the small-body surface, surface thermal parameters of the small body, and the shape and surface properties of spacecraft allowing for the computation of thermal radiation pressure, which may also be used for the generation of precise orbit determination solutions. After presenting the general model, an example application of the model for the OSIRIS-REx spacecraft in orbit about Asteroid (101955) Bennu is provided. Simulation studies were used to evaluate the effect of mismodeling of thermal radiation pressure on the spacecraft and study the use of the proposed method for generating precise orbit determination solutions

Realistic Covariance Generation for the GPM Spacecraft

A covariance realism process for NASA's Global Precipitation Measurement (GPM) spacecraft is detailed. The GPM spacecraft is in a low earth orbit, and performs collision avoidance maneuvers few times a year. Currently GPM is below the International Space Station (ISS). So, in addition to cataloged debris objects, GPM must contend with smallsat/cubesat objects that are deployed from the ISS. Both operational scenarios require complete knowledge of the expected GPM prediction errors as a function of time. In this study, we present a method for generating realistic predicted covariance that uses linear propagation of the covariance with the addition of process noise. Further analyses are presented for the process noise ''tuning'' that generates an inflation factor based on the observed error statistics of the predictive satellite trajectories when compared to the definitive ones. Different tuning strategies are considered and compared via a Goodness-of-Fit testing for the Gaussian properties of the scaled covariance. SpaceNav's realistic covariance generation approach takes into account the contribution of predicted maneuver errors in the increased propagation uncertainty. Corresponding maneuver uncertainty is injected into the state uncertainty, and is used within the collision avoidance process to determine the collision risk for close approach events that follow a maneuver. This is a critical step in the maneuver planning process that provides the satellite operator with an accurate quantification of the collision probability for planned maneuvers. Using this information, an informed decision can be made to proceed with a maneuver if the collision risk is acceptable. This approach is validated by Monte-Carlo simulations and results are presented

A study of socio-cultural elements in common proverbs in Khorasan Razavi with emphasis on Kashmar city

One of the manifestations of culture and civilization and even literature of any country is the proverbs, rulings and short and rich words that arise from the greats of science and literature or from the common people and in our vast and ancient language there are thousands of proverbs and words Which has taste, thought and kindness and good interpretation in saying the meaning. The people of a society, when they find their experiences and reserves and those of the past as accepted and certain facts, express them in short sentences, in the form of poetry or prose, so that when they use them, the audience Immerse yourself in deep thought and leave a lasting impression on him. In fact, proverbs are the essence of a nation's collective wisdom that has been polished over time and passed down to us heart to heart. In our country, due to its ancient history, there are many proverbs. Although in different Iranian ethnic groups these proverbs have differences in language and dialect, but many of them are common in terms of meaning or concept. This article tries to examine the socio-cultural elements of the proverbs common in Kashmar city, its roots, dialect and their uses

A study of socio-cultural elements in common proverbs in Khorasan Razavi with emphasis on Kashmar city

One of the manifestations of culture and civilization and even literature of any country is the proverbs, rulings and short and rich words that arise from the greats of science and literature or from the common people and in our vast and ancient language there are thousands of proverbs and words Which has taste, thought and kindness and good interpretation in saying the meaning. The people of a society, when they find their experiences and reserves and those of the past as accepted and certain facts, express them in short sentences, in the form of poetry or prose, so that when they use them, the audience Immerse yourself in deep thought and leave a lasting impression on him. In fact, proverbs are the essence of a nation's collective wisdom that has been polished over time and passed down to us heart to heart. In our country, due to its ancient history, there are many proverbs. Although in different Iranian ethnic groups these proverbs have differences in language and dialect, but many of them are common in terms of meaning or concept. This article tries to examine the socio-cultural elements of the proverbs common in Kashmar city, its roots, dialect and their uses

Frequency chirping of energetic particle driven modes in tokamaks; Self-consistent modelling and simulation

Long range frequency chirping waves have been observed in various plasma experiments. Theoretical toy models and simulations show that the nonlinear saturation of an initially unstable plasma wave driven by energetic particles may lead to the emergence of chirping waves. In toroidal configurations, these waves can lead to ejection of the particles from the hot core of the plasma and degrade the machine performance. Therefore, it is essential to develop theory and simulation models to better understand and control chirping waves in future fusion plasmas, such as ITER. Fast particles of tokamaks can destabilize plasma waves. Previous numerical simulations have revealed that an isolated Alfven eigenmode can evolve into chirping signals if the mode is subject to intrinsic damping into the cold plasma. In 1997, Berk-Breizman and co-workers studied the nonlinear stage of an excited electrostatic plasma wave where chirping signals were observed and interpreted as Bernstein-Greene-Kruskal waves with sweeping frequencies. These chirping waves are associated with coherent structures, the so-called "holes" and "clumps", in phase space of energetic particles. Such structures found to move adiabatically which implies the particles can be carried with the waves; so called convective transport. During long ranges of frequency chirping, the spatial profile of the wave can change considerably and hence new models are required to study long range frequency chirping of Alfvenic perturbations. In 2010, a 1D electrostatic nonperturbative model was developed by Breizman for an adiabatic study of chirping waves as a 1D paradigm of their electromagnetic counterparts. In order to build more realistic models, nonperturbative theory needs to be extended to electromagnetic waves and also fast particle orbital dynamics should be captured. In this work, a model is developed to investigate the effect of fast particle dynamics in tokamaks using a 1D description. This new trapped/passing model demonstrates how energetic particle orbits can impact the non-linear behaviour of the waves. The evolution of the wave radial profile as well as the rate of frequency chirping as a function of the fast particles orbits are studied. As the next step, the theory of adiabatic frequency chirping is developed for Alfvenic-type perturbations in realistic configurations. The impact of long range frequency deviations on the radial profile of a global Alfven eigenmode is studied and the chirping rate analysed. In this model, the radial component of the wave is described using the method of finite elements and the total Lagrangian of the system is varied with respect to the weight of each finite element. Also, exact constants of motion during the long range frequency chirping are introduced. In this work, the theory of chirping waves is extended further by investigating the impact of particle trapping in phase-space for a growing wave potential in the orbital model introduced above. In this respect, a phase space waterbag model is developed by using Lagrangian contours to discretize the phase-space island in adiabatic invariants. In addition, a study of the influence of higher particle resonances on the behaviour of chirping waves is also performed. Finally, self-consistent simulations are performed using the hybrid model of the MEGA code to illustrate convective transport of energetic particles in tokamaks. A novel phase-space analysis tool is built which enables a reduction of particle dynamics to a 1D picture. This is based on a new conservation law for particle dynamics which remains valid even when frequency changes. Therefore, it is possible to observe the evolution of holes and clumps on appropriate sub-slices of fast particles phase-space. For a toroidicity-induced Alfven eigenmode, the mechanism of frequency chirping phenomenon has been clarified. The observations of the wave behaviour are consistent with the adiabatic theory

Construction and Evaluation of The Wind Tunnel Technique for Estimating Ammonia Volatilization from Land

Agriculture is mainly responsible for ammonia (NH3) volatilization. Among all agricultural activities, livestock and especially animal manures are the most important sources of NH3 emissions. Manure application which not only exacerbate greenhouse gas emissions, but also leads to eutrophication of water bodies. Many studies have shown that surface application of manure can lead to large ammonia losses and run off, on the other hand that tillage can substantially reduce these losses. It is necessary to determine ammonia flux from manure-amended soils to improve management manure handling practices for minimizing agriculture’s impact on the environment. From this point of view, one of the direct measured method was used to determine this volatilization. The objections of this work were: i) The design, construction, physical calibration, and operation of the little wind tunnels. ii) Recover ammonia loss from bovine slurry by little wind tunnel method. iii) Determine the effect of slurry application depth on ammonia emission. The little wind tunnel system consisted of plastic canopy covering the treatment area (2 m long by 0.5 m wide). By was using a fan, it was imitated the natural wind speed in the test area (1-1.5 m/s). Nitrogen losses were measured with this method in surface application, 50 mm and 100 mm subsurface. In the surface application, the highest ammonia emission was observed. It was approximately 68% higher in compared to another methods. There is significantly (P=0.05) different in the ammonia emission, between the surface apply method and injection manure in soil methods. But There isn’t any significantly different between ammonia emission amount in injection subsurface methods (100 mm and 50 mm deep)