Reconstruction study on the plan and section of the \u27Can Chanh Dien\u27 main palace of the Nguyen dynasty

制度:新 ; 報告番号:甲2805号 ; 学位の種類:博士(建築学) ; 授与年月日:2009/3/15 ; 早大学位記番号:新502

Comportement des bétons autoplaçants par temps chaud

L'autoplaçance, ou aptitude du béton frais à s'écouler sous l'effet de la gravité et sans apport extérieur d'énergie (vibration), est obtenue en utilisant un plus grand nombre de constituants, comparativement aux bétons traditionnels vibrés, notamment des additions minérales et au moins une addition chimique de type superplastifiant. La complexité des interactions entre les constituants conduisant à l'autoplaçance a été antérieurement démontrée et maîtrisée à la température du laboratoire. L'objectif de ce travail est de caractériser l'autoplaçance dans des conditions de température telles qu'elles prévalent en situation de temps chaud et de regarder quelles sont les conséquences de ces conditions thermiques sur les propriétés à l'état durci du béton. Le programme expérimental permet de reproduire en laboratoire les conditions d'un bétonnage par temps chaud, à la fois lors de la confection du mélange et lors de la maturation des éprouvettes de contrôle habituellement réalisées sur chantier. Les paramètres de l'étude sont donc la température initiale du béton, les moyens de maintenir l'autoplaçance obtenue à la température de 20°C (ajout d'eau ou surdosage en superplastifiant), la conservation des éprouvettes et la formulation des bétons. Les résultats obtenus montrent que les moyens de maintenir l'autoplaçance à température initiale élevée n'induisent pas de variations significatives de la compacité du béton. Il en résulte des propriétés à l'état durci identiques ou meilleures que celles mesurées à 20°C. La conservation des éprouvettes à une température élevée durant les premières 24 heures simulant des conditions non normalisées n'altère pas les propriétés. Une analyse plus fine prenant en compte la maturité, la compacité et les caractéristiques de l'hydratation (quantités d'hydrates et cinétique) permet de mettre en évidence l'intérêt d'utiliser une matrice à forte teneur en filler calcaire. Finalement, les résultats viennent confirmer ceux relevés dans la littérature, à savoir que les effets d'une température élevée ne sont pas aussi préjudiciables sur les propriétés du BAP que sur celles des bétons traditionnels vibrés. Pour autant, les recommandations existantes lors d'un bétonnage par temps chaud doivent toujours être considérées ; leur respect permet en effet d'éviter une déformation différée excessive sous chargement, observée dans cette étude pour le BAP incorporant un liant ternaire (clinker, filler calcaire et laitier) lorsqu'il est confectionné et mûri à températures élevées.The self-compacting ability, or ability of the fresh concrete to flow under the effect of gravity without external energy (vibration) is obtained by using more components in comparison with conventional vibrated concrete, including mineral additions and at least one chemical addition of superplasticizer types. The complex interactions between these components leading to the self-compactibility has been previously demonstrated and controlled at the temperature conditions in the laboratory. The objective of this work is to characterize the self-compactibility in temperature conditions prevalent in hot weather situation and to know what are the consequences of these thermal conditions on the properties of the cured concrete. The experimental program reproduced in the laboratory the conditions of hot weather concreting, during the preparation of the mixture and the maturation of control specimens which are usually done on site. The study parameters are the initial temperature of the concrete, the means to maintain the self-compacting ability obtained at a temperature of 20°C (addition of water or overdose of superplasticizer), the conservation of specimens and the concrete design. The obtained results show that the means to maintain the self-compatibility at high initial temperature does not induce significant changes in the concrete compactness. As a result, the properties in the hardened state are equal or better than those measured at 20°C. Conservation of specimens at a high temperature during the first 24 hours which simulates non-standard conditions does not alter the properties. A more detailed analysis taking into account the maturity, the compactness and the characteristics of hydration (amount of hydrates and kinetics) allows highlighting the advantages of using a matrix with a high content of limestone filler. Finally, the results confirm some literature data and show that the effects of high temperature on the properties of BAP are not as detrimental as those obtained on conventional vibrated concrete. However, the existing recommendations for hot weather concreting should always be considered, and the respect of these recommendations makes it possible to avoid excessive delayed strain under loading observed in the case of the BAP incorporating a ternary binder (clinker, limestone filler and slag) when mixed and matured at high temperature

Stability of Cracked Plates with Nonlinearly Variable Thickness Resting on Elastic Foundations

In this paper, the stability of rectangular cracked plates with nonlinearly variable thickness resting on the elastic foundations is studied. The thickness of the plate varies exponentially along the x-axis. Meanwhile, the elastic foundation is modeled by a two-parameter Pasternak elastic foundation type. The crack is assumed at the center of the plate with variable length and angle of inclination. The establishment of the stability equations of the cracked plate is based on the Higher Order Shear Deformation Theory (HSDT) combined with the phase field theory. Next, using the finite element method to solve the equations to find the minimum force that causes plate instability. To test the reliability of the computational theory, the results are compared with several reputable published papers. Then, the article will investigate the influence of elastic foundation, crack location, crack length and crack inclination on the stability of plate. The results show that the elastic foundation has a great influence on the plate stability, while the crack inclination angle has less influence. Finally, there are some images of the destabilization patterns of cracked plates placed on an elastic foundation

Experimental study of short concrete columns reinforced with GFRP bars under monotonic loading

The glass fiber reinforced polymer (GFRP) bars are considered as an alternative reinforcement to steel in concrete structures subjected to chloride environment because of their non- corrosive and non-magnetic properties. To examine the applicability of GFRP bars to performance of concrete columns, this work was conducted. The effect of the compressive reinforcement ratio and stirrup spacing on the load carrying capacity of concrete columns reinforced with GFRP bars is experimentally investigated. Nine short concrete columns with dimensions of 150 × 150 × 600 mm were cast and tested until failure under displacement-controlled concentric loading. The experimental results demonstrated that by increasing the reinforcement ratio from 0.37% to 3.24%, the load-bearing capacity of GFRP RC columns was found to increase by an average of 28%. Moreover, the tested results confirmed that the GFRP stirrup spacing had a significant influence on the load-carrying capacity of the columns

Experimental study of short concrete columns reinforced with GFRP bars under monotonic loading

The glass fiber reinforced polymer (GFRP) bars are considered as an alternative reinforcement to steel in concrete structures subjected to chloride environment because of their non- corrosive and non-magnetic properties. To examine the applicability of GFRP bars to performance of concrete columns, this work was conducted. The effect of the compressive reinforcement ratio and stirrup spacing on the load carrying capacity of concrete columns reinforced with GFRP bars is experimentally investigated. Nine short concrete columns with dimensions of 150 × 150 × 600 mm were cast and tested until failure under displacement-controlled concentric loading. The experimental results demonstrated that by increasing the reinforcement ratio from 0.37% to 3.24%, the load-bearing capacity of GFRP RC columns was found to increase by an average of 28%. Moreover, the tested results confirmed that the GFRP stirrup spacing had a significant influence on the load-carrying capacity of the columns

Stability of Cracked Plates with Nonlinearly Variable Thickness Resting on Elastic Foundations

In this paper, the stability of rectangular cracked plates with nonlinearly variable thickness resting on the elastic foundations is studied. The thickness of the plate varies exponentially along the x-axis. Meanwhile, the elastic foundation is modeled by a two-parameter Pasternak elastic foundation type. The crack is assumed at the center of the plate with variable length and angle of inclination. The establishment of the stability equations of the cracked plate is based on the Higher Order Shear Deformation Theory (HSDT) combined with the phase field theory. Next, using the finite element method to solve the equations to find the minimum force that causes plate instability. To test the reliability of the computational theory, the results are compared with several reputable published papers. Then, the article will investigate the influence of elastic foundation, crack location, crack length and crack inclination on the stability of plate. The results show that the elastic foundation has a great influence on the plate stability, while the crack inclination angle has less influence. Finally, there are some images of the destabilization patterns of cracked plates placed on an elastic foundation

Investigation of Ultrasonic Pulse Velocity Reduction in Reinforced Concrete Members Exposed to High Temperature

Nowadays, the fire resistance of reinforced concrete members is generally defined by material characteristics at elevated temperatures and temperature functions. However, the influence of steel reinforcement in concrete members exposed to high temperatures on the ultrasonic pulse velocity (UPV) measurements has still been limited. In this paper, the quality of concrete and steel reinforcement/concrete interface was assessed under high temperatures using UPV measurements. The specimens were classified into four categories: the control tested cubes without rebar; tested cubes with plain and ribbed steel rebars. Tested cubes with dimensions of 100x100x100 mm were cast and cured for 28 days at room temperature (20oC). After drying all specimens at 105oC for 48 hours, these cubes were subjected to four different temperature levels ranging from 150oC to 400oC for 4 hours before being cooled to room temperature. According to the measured values of UPV, the higher the temperature attained in specimens, the greater the following changes occurred in concrete: (i) the degradation within the concrete; (ii) the debonding of steel reinforcements in concrete

Investigation of Ultrasonic Pulse Velocity Reduction in Reinforced Concrete Members Exposed to High Temperature

Nowadays, the fire resistance of reinforced concrete members is generally defined by material characteristics at elevated temperatures and temperature functions. However, the influence of steel reinforcement in concrete members exposed to high temperatures on the ultrasonic pulse velocity (UPV) measurements has still been limited. In this paper, the quality of concrete and steel reinforcement/concrete interface was assessed under high temperatures using UPV measurements. The specimens were classified into four categories: the control tested cubes without rebar; tested cubes with plain and ribbed steel rebars. Tested cubes with dimensions of 100x100x100 mm were cast and cured for 28 days at room temperature (20oC). After drying all specimens at 105oC for 48 hours, these cubes were subjected to four different temperature levels ranging from 150oC to 400oC for 4 hours before being cooled to room temperature. According to the measured values of UPV, the higher the temperature attained in specimens, the greater the following changes occurred in concrete: (i) the degradation within the concrete; (ii) the debonding of steel reinforcements in concrete

Concrete beams using seawater and sea sand reinforced with steel and GFRP rebars exposed to marine environment: An experimental study

Using fresh water and river sand in concrete mix composition makes a lot of negative impacts on resources and the environment while the source of sea sand and sea water is abundant and less harmful to the environment. However, sea sand and seawater in concrete can cause severe corrosion of the reinforcement, reducing the durability and bearing capacity of the structure. This paper illustrates the results of a comparative study on the flexural behavior of six corroded seawater sea-sand concrete (SWSSC) beams. The corrosion process of two concrete beams reinforced with traditional steel bars and four concrete beams reinforced with a combination of glass fiber reinforced polymer (GFRP) and steel bars was coupled by the effect of seawater exposure and sustained load. It was found that after exposure to a marine environment during the period of 60 months the GFRP bar retains surface integrity, meanwhile, the steel bars were significantly corroded with a cross-sectional area loss of approximately 13.93%. The decrease in bending stiffness, yield load, and ultimate load of the RC beams was found due to the deterioration of SWSSC and corrosion of steel bars.

Concrete beams using seawater and sea sand reinforced with steel and GFRP rebars exposed to marine environment: An experimental study

Using fresh water and river sand in concrete mix composition makes a lot of negative impacts on resources and the environment while the source of sea sand and sea water is abundant and less harmful to the environment. However, sea sand and seawater in concrete can cause severe corrosion of the reinforcement, reducing the durability and bearing capacity of the structure. This paper illustrates the results of a comparative study on the flexural behavior of six corroded seawater sea-sand concrete (SWSSC) beams. The corrosion process of two concrete beams reinforced with traditional steel bars and four concrete beams reinforced with a combination of glass fiber reinforced polymer (GFRP) and steel bars was coupled by the effect of seawater exposure and sustained load. It was found that after exposure to a marine environment during the period of 60 months the GFRP bar retains surface integrity, meanwhile, the steel bars were significantly corroded with a cross-sectional area loss of approximately 13.93%. The decrease in bending stiffness, yield load, and ultimate load of the RC beams was found due to the deterioration of SWSSC and corrosion of steel bars.