Cement has been traditionally used as a main binding material of high ductile fiber reinforced ce... more Cement has been traditionally used as a main binding material of high ductile fiber reinforced cementitious composites. The purpose of this paper is to investigate the feasibility of using alkali-activated slag and polyvinyl alcohol (PVA) fibers for manufacturing high ductile fiber reinforced cementless composites. Two mixture proportions with proper flowability and mortar viscosity for easy fiber mixing and uniform fiber dispersion were selected based on alkali activators. Then, the slump flow, compression, uniaxial tension and bending tests were performed on the mixes to evaluate the basic properties of the composites. The cementless composites showed an average slump flow of 465 mm and tensile strain capacity of approximately 2% of due to formation of multiple micro-cracks. Test results demonstrated a feasibility of manufacturing high ductile fiber reinforced composites without using cement.
The current study presents an algorithm of the long-term behavior analysis of cable stayed bridge... more The current study presents an algorithm of the long-term behavior analysis of cable stayed bridge with PSC girders using high-performance concrete (HPC), which concrete was cast for high-strength and enhancing elastic modulus. The prediction of time-dependent behavior of HPC members is modeled by improving the AASHTO-LRFD (2004) method for normal concrete in the prediction of creep, shrinkage, and relaxation of tendon. The long term analysis was performed to determine the effects of creep and shrinkage of concrete, additionally, with the effect of construction stages varying with time. The developed model for prediction of HPC material has been applied in the long-term analysis of cable-stayed bridges to compare with the several types of concrete. By using HPC to compare with normal concrete, it gives some advantages in the design of PSC cable-stayed bridges that axial and transverse deflections of girders can reduce and the result may minimize the size of HPC girders, overall weigh...
This paper presents an algorithm of the time-dependent analysis of cable stayed bridge with PSC s... more This paper presents an algorithm of the time-dependent analysis of cable stayed bridge with PSC segmental box girder types for design practice. Applied loading conditions at the early stage of construction were self-weight, time-dependent effects and additional construction load. The long term analysis was performed to determine the effects of creep and shrinkage of concrete, respectively. From the result, we can get all information on the behaviors of cable stayed elements not only during entire construction stages but also after construction for long term behaviors. The developed program can be easy to apply for the design of such a cable stayed bridge structure as well as for the evaluation of short and long term behaviors of the structure.
Three-dimensional finite element model for analysis of reinforced concrete members was developed ... more Three-dimensional finite element model for analysis of reinforced concrete members was developed in order to investigate the prediction of bending and shear failure of reinforced concrete beams. A failure surface of concrete in strain space was newly proposed in order to predict accurately the ductile response of concrete under multi-axial confining stresses. Cracking of concrete in triaxial state was incorporated with considering the tensile strain-softening behavior of cracked concrete as well as the cracked shear behavior on cracked surface of concrete caused by aggregate interlocking and, dowel action. By correlation study on failure types of bending and shear of beams, current finite element model was well simulated not only the type of ductile bending failure of under-reinforced beams but also the type of brittle shear failure of no-stirruped reinforced concrete beam.
h i g h l i g h t s CFBC bottom ash was used as an expansion agent in OPC and slag cement. Cracki... more h i g h l i g h t s CFBC bottom ash was used as an expansion agent in OPC and slag cement. Cracking potential was evaluated by direct tensile and shrinkage tests. Ash delayed cracking times due to its shrinkage compensation. This cracking times varied with the drying condition rather than ash content.
Based on the orthotropic hypoelasticity formulation, a triaxial constitutive model of concrete is... more Based on the orthotropic hypoelasticity formulation, a triaxial constitutive model of concrete is proposed. To account for increasing ductility in high confinement of concrete, the ductility enhancement is considered using so called the strain enhancement factor. It is also developed a three-dimensional finite element model for reinforced concrete structural members based on the proposed constitutive law of concrete with the smeared crack approach. The concrete confinement effects due to the beam-column joint are investigated through numerical examples for simple beam and structural beam member. Concrete at compression fibers in the vicinity of beam-column joint behaves dominant not only by the uniaxial compressive state but also by the biaxial and triaxial compressive states. For the reason of the severe confinement of concrete in the beam-column joint, the flexural critical cross-section is observed at a small distance away from the beam-column joint. These observations should be utilized for the economic design when the concrete structural members are subjected to high confinement due to the influence of beam-column joint.
ABSTRACT This paper presents the mix composition and production method that was applied to an ext... more ABSTRACT This paper presents the mix composition and production method that was applied to an extruded Ductile Fiber Reinforced Cement Composite (DFRCC) panel, as well as the flexural performance, represented by deformation hardening behavior with multiple cracking. The effect of fiber distribution characteristics on the flexural behavior of the panel is also addressed. In order to demonstrate the fiber distribution effect, a series of experiments and analyses, including a sectional image analysis and micromechanical analysis, was performed. From the experimental and analysis results, it was found that the flexural behavior of the panel was highly affected by a slight variation in the mix composition. In terms of the average fiber orientation, the fiber distribution was found to be similar to that derived under the assumption of a two-dimensional random distribution, irrespective of the mix composition. In contrast, the probability density function for the fiber orientation was measured to vary depending on the mix composition.
The carbon dioxide (CO2) emission during the ordinary Portland cement (OPC) manufacturing process... more The carbon dioxide (CO2) emission during the ordinary Portland cement (OPC) manufacturing process is up to about 7.0 % of global manmade CO2. The OPC is also known to have toxic substances. The purpose of current research is to develop an environmentally green and high-ductile fiber low-cement composite (HDFLC) in which the binder is mixed by replacing the amount of the cement of 60% as the ground granulated blast-furnace slag (GGBS) with or without using alkali activators. The material and mechanical characteristics of the HDFLC were evaluated experimentally by the slump flow, compression, and direct tension tests.
This paper presents the crack control of reinforcement concrete composite slabs which were produc... more This paper presents the crack control of reinforcement concrete composite slabs which were produced with the extruded ECC panel. Cracking control performance was evaluated based on the flexural tests on real scale one-way slabs manufactured with or without ECC panel.
This paper presents the mix composition, production method, and curing condition applied to the e... more This paper presents the mix composition, production method, and curing condition applied to the extruded ECC(Engineered Cementitious Composite) panel which are able to exhibit multiple cracking and potential pseudo strain-hardening behavior. In addition to the production technique of extruded ECC panel, the effect of fiber distribution characteristics, which are uniquely created by applying extrusion process, on the flexural behavior of the panel is also focussed. In order to demonstrate fiber distribution, a series of experiments and analyses, including image processing/analysis and micro-mechanical analysis, was performed. The optimum mix composition of extruded ECC panel was determined in terms of water matrix ratio, the amount of cement, ECC powder, and silica powder. It was found that flexural behavior of extruded ECC panel was highly affected by the slight difference in mix composition of ECC panel. This is mainly because the difference in mix composition results in the change of micro-mechanical properties as well as fiber distribution characteristics, represented by fiber dispersion and orientation. In terms of the average fiber orientation, the fiber distribution was found to be similar to the assumption of two dimensional random distribution, irrespective of mix composition. In contrast, the probability density function for fiber orientation was measured to be quite different depending on the mix composition.
Since the early 1990s, many studies were conducted to utilize waste tires as a replacement for na... more Since the early 1990s, many studies were conducted to utilize waste tires as a replacement for natural coarse and fine aggregates in concrete, known as rubberized concrete or rubber-concrete. In this paper, an experimental study was performed on the strength properties of concrete containing fine-rubber particles as a replacement of fine aggregate, using destructive and non-destructive tests. Ultrasonic pulse velocity (UPV) tests were used to evaluate the strength property of rubber-concrete as a non-destructive test. Compressive and splitting tensile strengths were determined for four different volume contents of fine-rubber particles and exponential equations were proposed for the relationship between compressive, splitting tensile strength and the UPV of rubber-concrete, respectively. With the limited conditions in this paper, it found that UPV tests could also be used to estimate the compressive and tensile strengths of rubber-concrete, that are used in other types of concrete.
The present study concerns a development of calcium aluminate cement (CAC) concrete to enhance th... more The present study concerns a development of calcium aluminate cement (CAC) concrete to enhance the durability against an externally chemically aggressive environment, in particular, chloride-induced corrosion. To evaluate the inhibition effect and concrete properties, CAC was partially mixed with ordinary Portland cement (OPC), ranging from 5% to 15%, as a binder. As a result, it was found that an increase in the CAC in binder resulted in a dramatic decrease in the setting time of fresh concrete. However, the compressive strength was lower, ranging about 20 MPa, while OPC indicated about 30-35 MPa at an equivalent age. When it comes to chloride transport, there was only marginal variation in the diffusivity of chloride ions. The corrosion resistance of CAC mixture was significantly enhanced: its chloride threshold level for corrosion initiation exceeded 3.0% by weight of binder, whilst OPC and CAC concrete indicated about 0.5%-1.0%.
It is proposed that an highly accurate algorithm can be used for the nonlinear beam-column fiber ... more It is proposed that an highly accurate algorithm can be used for the nonlinear beam-column fiber element with non prismatic steel sections based on the two field mixed finite element formulation. Displacement shape function is not necessary in the two-field mixed formulation, while section force interpolation function derived from section equilibrium is used. Due to the force interpolation function is exact, the equilibrium in element level and section level is exactly satisfied and more accurate nonlinear analysis is possible. Through the parametric studies, the mixed formulation shows more accurate results than displacement-based formulation in curvature and moment distributions and in the overall structural load-displacement relations.
Two methods of the nonlinear static pushover analysis have been presented for the performance-bas... more Two methods of the nonlinear static pushover analysis have been presented for the performance-based seismic design and evaluation of MDOF continuous bridges. Guidelines for buildings presented in FEMA-273 applying the Displacement Coefficient Method (DCM) and in ATC applying the Capacity Spectrum Method(CSM) have been modified for MDOF bridges. Two methods are compared with the time- history analysis. The lateral load distribution pattern for seismic loads has been examined in the static pushover analysis. The force-based fiber frame finite element has been implemented in the modeling of reinforced concrete piers.
In this research, reinforced concrete (RC) and strain-hardening cementitious composite (SHCC) col... more In this research, reinforced concrete (RC) and strain-hardening cementitious composite (SHCC) columns subjected to lateral loads combined with a constant load were investigated, both by experiments and predictions, with two distributed inelastic finite element models established by the stiffness and flexibility formulations. SHCC applied in the column plastic hinge region could not only enhance the lateral load and displacement capacities of columns but also offer effective advantages in the control of bending and shear cracks induced by multiple microcracks, the prevention of the spalling of cover concrete, and the resistance to buckling of steel bars. With the layered cross-sectional approach using constitutive laws of SHCC considering a proposed model of the post-cracked high-ductile tensile characteristics, as well as concrete and reinforcing steel bars, an inelastic beam-column finite element model was presented with a distributed flexibility formulation. In comparison with exp...
Cement has been traditionally used as a main binding material of high ductile fiber reinforced ce... more Cement has been traditionally used as a main binding material of high ductile fiber reinforced cementitious composites. The purpose of this paper is to investigate the feasibility of using alkali-activated slag and polyvinyl alcohol (PVA) fibers for manufacturing high ductile fiber reinforced cementless composites. Two mixture proportions with proper flowability and mortar viscosity for easy fiber mixing and uniform fiber dispersion were selected based on alkali activators. Then, the slump flow, compression, uniaxial tension and bending tests were performed on the mixes to evaluate the basic properties of the composites. The cementless composites showed an average slump flow of 465 mm and tensile strain capacity of approximately 2% of due to formation of multiple micro-cracks. Test results demonstrated a feasibility of manufacturing high ductile fiber reinforced composites without using cement.
The current study presents an algorithm of the long-term behavior analysis of cable stayed bridge... more The current study presents an algorithm of the long-term behavior analysis of cable stayed bridge with PSC girders using high-performance concrete (HPC), which concrete was cast for high-strength and enhancing elastic modulus. The prediction of time-dependent behavior of HPC members is modeled by improving the AASHTO-LRFD (2004) method for normal concrete in the prediction of creep, shrinkage, and relaxation of tendon. The long term analysis was performed to determine the effects of creep and shrinkage of concrete, additionally, with the effect of construction stages varying with time. The developed model for prediction of HPC material has been applied in the long-term analysis of cable-stayed bridges to compare with the several types of concrete. By using HPC to compare with normal concrete, it gives some advantages in the design of PSC cable-stayed bridges that axial and transverse deflections of girders can reduce and the result may minimize the size of HPC girders, overall weigh...
This paper presents an algorithm of the time-dependent analysis of cable stayed bridge with PSC s... more This paper presents an algorithm of the time-dependent analysis of cable stayed bridge with PSC segmental box girder types for design practice. Applied loading conditions at the early stage of construction were self-weight, time-dependent effects and additional construction load. The long term analysis was performed to determine the effects of creep and shrinkage of concrete, respectively. From the result, we can get all information on the behaviors of cable stayed elements not only during entire construction stages but also after construction for long term behaviors. The developed program can be easy to apply for the design of such a cable stayed bridge structure as well as for the evaluation of short and long term behaviors of the structure.
Three-dimensional finite element model for analysis of reinforced concrete members was developed ... more Three-dimensional finite element model for analysis of reinforced concrete members was developed in order to investigate the prediction of bending and shear failure of reinforced concrete beams. A failure surface of concrete in strain space was newly proposed in order to predict accurately the ductile response of concrete under multi-axial confining stresses. Cracking of concrete in triaxial state was incorporated with considering the tensile strain-softening behavior of cracked concrete as well as the cracked shear behavior on cracked surface of concrete caused by aggregate interlocking and, dowel action. By correlation study on failure types of bending and shear of beams, current finite element model was well simulated not only the type of ductile bending failure of under-reinforced beams but also the type of brittle shear failure of no-stirruped reinforced concrete beam.
h i g h l i g h t s CFBC bottom ash was used as an expansion agent in OPC and slag cement. Cracki... more h i g h l i g h t s CFBC bottom ash was used as an expansion agent in OPC and slag cement. Cracking potential was evaluated by direct tensile and shrinkage tests. Ash delayed cracking times due to its shrinkage compensation. This cracking times varied with the drying condition rather than ash content.
Based on the orthotropic hypoelasticity formulation, a triaxial constitutive model of concrete is... more Based on the orthotropic hypoelasticity formulation, a triaxial constitutive model of concrete is proposed. To account for increasing ductility in high confinement of concrete, the ductility enhancement is considered using so called the strain enhancement factor. It is also developed a three-dimensional finite element model for reinforced concrete structural members based on the proposed constitutive law of concrete with the smeared crack approach. The concrete confinement effects due to the beam-column joint are investigated through numerical examples for simple beam and structural beam member. Concrete at compression fibers in the vicinity of beam-column joint behaves dominant not only by the uniaxial compressive state but also by the biaxial and triaxial compressive states. For the reason of the severe confinement of concrete in the beam-column joint, the flexural critical cross-section is observed at a small distance away from the beam-column joint. These observations should be utilized for the economic design when the concrete structural members are subjected to high confinement due to the influence of beam-column joint.
ABSTRACT This paper presents the mix composition and production method that was applied to an ext... more ABSTRACT This paper presents the mix composition and production method that was applied to an extruded Ductile Fiber Reinforced Cement Composite (DFRCC) panel, as well as the flexural performance, represented by deformation hardening behavior with multiple cracking. The effect of fiber distribution characteristics on the flexural behavior of the panel is also addressed. In order to demonstrate the fiber distribution effect, a series of experiments and analyses, including a sectional image analysis and micromechanical analysis, was performed. From the experimental and analysis results, it was found that the flexural behavior of the panel was highly affected by a slight variation in the mix composition. In terms of the average fiber orientation, the fiber distribution was found to be similar to that derived under the assumption of a two-dimensional random distribution, irrespective of the mix composition. In contrast, the probability density function for the fiber orientation was measured to vary depending on the mix composition.
The carbon dioxide (CO2) emission during the ordinary Portland cement (OPC) manufacturing process... more The carbon dioxide (CO2) emission during the ordinary Portland cement (OPC) manufacturing process is up to about 7.0 % of global manmade CO2. The OPC is also known to have toxic substances. The purpose of current research is to develop an environmentally green and high-ductile fiber low-cement composite (HDFLC) in which the binder is mixed by replacing the amount of the cement of 60% as the ground granulated blast-furnace slag (GGBS) with or without using alkali activators. The material and mechanical characteristics of the HDFLC were evaluated experimentally by the slump flow, compression, and direct tension tests.
This paper presents the crack control of reinforcement concrete composite slabs which were produc... more This paper presents the crack control of reinforcement concrete composite slabs which were produced with the extruded ECC panel. Cracking control performance was evaluated based on the flexural tests on real scale one-way slabs manufactured with or without ECC panel.
This paper presents the mix composition, production method, and curing condition applied to the e... more This paper presents the mix composition, production method, and curing condition applied to the extruded ECC(Engineered Cementitious Composite) panel which are able to exhibit multiple cracking and potential pseudo strain-hardening behavior. In addition to the production technique of extruded ECC panel, the effect of fiber distribution characteristics, which are uniquely created by applying extrusion process, on the flexural behavior of the panel is also focussed. In order to demonstrate fiber distribution, a series of experiments and analyses, including image processing/analysis and micro-mechanical analysis, was performed. The optimum mix composition of extruded ECC panel was determined in terms of water matrix ratio, the amount of cement, ECC powder, and silica powder. It was found that flexural behavior of extruded ECC panel was highly affected by the slight difference in mix composition of ECC panel. This is mainly because the difference in mix composition results in the change of micro-mechanical properties as well as fiber distribution characteristics, represented by fiber dispersion and orientation. In terms of the average fiber orientation, the fiber distribution was found to be similar to the assumption of two dimensional random distribution, irrespective of mix composition. In contrast, the probability density function for fiber orientation was measured to be quite different depending on the mix composition.
Since the early 1990s, many studies were conducted to utilize waste tires as a replacement for na... more Since the early 1990s, many studies were conducted to utilize waste tires as a replacement for natural coarse and fine aggregates in concrete, known as rubberized concrete or rubber-concrete. In this paper, an experimental study was performed on the strength properties of concrete containing fine-rubber particles as a replacement of fine aggregate, using destructive and non-destructive tests. Ultrasonic pulse velocity (UPV) tests were used to evaluate the strength property of rubber-concrete as a non-destructive test. Compressive and splitting tensile strengths were determined for four different volume contents of fine-rubber particles and exponential equations were proposed for the relationship between compressive, splitting tensile strength and the UPV of rubber-concrete, respectively. With the limited conditions in this paper, it found that UPV tests could also be used to estimate the compressive and tensile strengths of rubber-concrete, that are used in other types of concrete.
The present study concerns a development of calcium aluminate cement (CAC) concrete to enhance th... more The present study concerns a development of calcium aluminate cement (CAC) concrete to enhance the durability against an externally chemically aggressive environment, in particular, chloride-induced corrosion. To evaluate the inhibition effect and concrete properties, CAC was partially mixed with ordinary Portland cement (OPC), ranging from 5% to 15%, as a binder. As a result, it was found that an increase in the CAC in binder resulted in a dramatic decrease in the setting time of fresh concrete. However, the compressive strength was lower, ranging about 20 MPa, while OPC indicated about 30-35 MPa at an equivalent age. When it comes to chloride transport, there was only marginal variation in the diffusivity of chloride ions. The corrosion resistance of CAC mixture was significantly enhanced: its chloride threshold level for corrosion initiation exceeded 3.0% by weight of binder, whilst OPC and CAC concrete indicated about 0.5%-1.0%.
It is proposed that an highly accurate algorithm can be used for the nonlinear beam-column fiber ... more It is proposed that an highly accurate algorithm can be used for the nonlinear beam-column fiber element with non prismatic steel sections based on the two field mixed finite element formulation. Displacement shape function is not necessary in the two-field mixed formulation, while section force interpolation function derived from section equilibrium is used. Due to the force interpolation function is exact, the equilibrium in element level and section level is exactly satisfied and more accurate nonlinear analysis is possible. Through the parametric studies, the mixed formulation shows more accurate results than displacement-based formulation in curvature and moment distributions and in the overall structural load-displacement relations.
Two methods of the nonlinear static pushover analysis have been presented for the performance-bas... more Two methods of the nonlinear static pushover analysis have been presented for the performance-based seismic design and evaluation of MDOF continuous bridges. Guidelines for buildings presented in FEMA-273 applying the Displacement Coefficient Method (DCM) and in ATC applying the Capacity Spectrum Method(CSM) have been modified for MDOF bridges. Two methods are compared with the time- history analysis. The lateral load distribution pattern for seismic loads has been examined in the static pushover analysis. The force-based fiber frame finite element has been implemented in the modeling of reinforced concrete piers.
In this research, reinforced concrete (RC) and strain-hardening cementitious composite (SHCC) col... more In this research, reinforced concrete (RC) and strain-hardening cementitious composite (SHCC) columns subjected to lateral loads combined with a constant load were investigated, both by experiments and predictions, with two distributed inelastic finite element models established by the stiffness and flexibility formulations. SHCC applied in the column plastic hinge region could not only enhance the lateral load and displacement capacities of columns but also offer effective advantages in the control of bending and shear cracks induced by multiple microcracks, the prevention of the spalling of cover concrete, and the resistance to buckling of steel bars. With the layered cross-sectional approach using constitutive laws of SHCC considering a proposed model of the post-cracked high-ductile tensile characteristics, as well as concrete and reinforcing steel bars, an inelastic beam-column finite element model was presented with a distributed flexibility formulation. In comparison with exp...
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