Showing papers in "Journal of Advanced Concrete Technology in 2006"
TL;DR: In this paper, the authors present design criteria to achieve saturated PSH behavior in fiber rupture type ECCs, which are measures of energy exchange during steady state flat crack propagation and stress level to initiate micro-cracks.
Abstract: Engineered Cementitious Composites (ECCs) have recently demonstrated their high performance with pseudo strain hardening (PSH) behavior in civil engineering structures and buildings. These materials incorporate low cost fibers such as Polyvinyl Alcohol fibers, which often rupture in composites. Such fiber rupture type ECCs tend to have inferior and unsaturated PSH behavior compared with those incorporating properly designed pull out type fiber. The present study focuses on presenting practical design criteria to achieve saturated PSH behavior in fiber rupture type ECCs. These criteria are proposed based on two performance indices, which are measures of energy exchange during steady state flat crack propagation and stress level to initiate micro-cracks. The latter performance index necessitates a new cracking strength prediction theory, which is proposed in the current study. Finally the cracking strength theory is justified using tensile test data, and the criteria are proposed based on the data in terms of these two indices.
251 citations
TL;DR: In this paper, the required performance and its criteria for high performance fiber reinforced cement composites (HPFRCC) are clarified for bridge decks, building dampers, retaining wall, irrigation channels and so forth.
Abstract: High Performance Fiber Reinforced Cement Composites (HPFRCC) show multiple cracking and strain-hardening behaviors in tension. Current applications in Japan include bridge decks, building dampers, retaining wall, irrigation channels and so forth. While the novel properties of HPFRCC are well known, the required performance and its criteria have not been clarified. For example, in addition to tensile load bearing capacity, protection against penetration of substance through fine cracks is also important. Clarification of the required performance and its criteria for HPFRCC is important to evaluate the design concepts of each application. This paper introduces recent applications using HPFRCC in Japan, focusing on required performance.
178 citations
TL;DR: In this article, the flexural behaviour of reinforced concrete beams produced from oil palm shell aggregates is investigated and compared with other lightweight concretes and the experimental results compare reasonably well with the current Codes of Practice.
Abstract: This paper presents an investigation on the flexural behaviour of reinforced concrete beams produced from oil palm shell (OPS) aggregates. Utilising OPS in concrete production not only solves the problem of disposing this solid waste but also helps conserve natural resources. A total of 6 under-reinforced beams with varying reinforcement ratios (0.52% to 3.90%) were fabricated and tested. Data presented include the deflection characteristics, cracking behaviour, ductility indices and end-rotations. The investigation revealed that the flexural behaviour of reinforced OPS concrete beams was comparable to that of other lightweight concretes and the experimental results compare reasonably well with the current Codes of Practice. It was observed that beams with low reinforcement ratios satisfied all the serviceability requirements as per BS 8110.
155 citations
TL;DR: In this paper, a non-linear bond stress-slip model for analyzing full-range strain distributions in FRP and shear bond stress distributions in the interface bond layer during pullout tests, along with a new anchorage length model and bond strength model were developed accordingly.
Abstract: The pullout test is a conventional test method for calibrating interfacial shear bond characteristics of Fiber Reinforced Polymer (FRP)-concrete interfaces. However, due to the small bending stiffness of FRP sheets/strips and the highly non-linear interface fracturing mechanism, a well-recognized analytical approach to the accurate interpretation of the pullout test results remains to be achieved despite extensive studies particularly when the aim is to calibrate a local bond stress-slip model, which is necessary for developing bond strength and anchorage length models avoiding the use of empirical formulations. This paper introduces a newly developed non-linear bond stress-slip model for analyzing full-range strain distributions in FRP and shear bond stress distributions in the interface bond layer during pullout tests, along with a new anchorage length model and bond strength model that were developed accordingly. Compared with other existing bond models, the bond model described here has two advantages besides its simplicity: (1) it incorporates the most important interface parameter, the so-called interfacial fracture energy, in all analytical processes and links it successfully with all other important bond parameters; (2) it is a general and unified approach that allows for the first time consideration of the effects of the adhesive bond layer in non-linear analysis of FRP-concrete interfaces. Further, a unified bond stress versus slip expression is formulated to show the differences in local bond stress-slip relationships at the loaded and free ends in pullout tests, so that the effects of the bond length used in a pullout test on the calibration of the interfacial bond stress-slip model can be clarified. The reliability of all proposed models is verified through a comprehensive comparison of the experimental and analytical results.
150 citations
TL;DR: A brief overview of the tensile test methods for concrete and cementitious composites can be found in this paper, where the results of a round robin test conducted as part of a project of the Japan Concrete Institute Technical Committee (JCI-TC) for Ductile Fiber-Reinforced Cementitious Composites (DFRCC) are introduced.
Abstract: This paper presents a brief overview of the tensile test methods for concrete and cementitious composites. Comparisons of uniaxial tension test results for a round robin test conducted as part of a project of the Japan Concrete Institute Technical Committee (JCI-TC) for Ductile Fiber-Reinforced Cementitious Composites (DFRCC) are introduced. Four types of tensile test methods for four types of DFRCC were used in this round robin test. The results differ according to the testing method and compacting direction of DFRCC. The relationships between the tensile test results and tensile characteristics calculated from bending test results are discussed. The possibility of establishing a standard test method for the evaluation of the tensile characteristics of DFRCC has been discussed by the Japan Concrete Institute Standard Committee. This discussion was based on the report of the JCI-TC and the results of the round robin test. Items that were discussed in further detail were (a) difficulties of uniaxial tension test as a standard test method, (b) treatment of DFRCC that does not have a strain hardening branch in tension, (c) adaptability of strain-based evaluation for cracked materials, and (d) relationship between uniaxial tensile characteristics and bending characteristics. The Standard Committee proposed the standard test method using the 4-point bending test to obtain bending moment–curvature curves. An evaluation method for the tensile strength and ultimate strain of DFRCC was added as an appendix of non-mandatory information. This method is considered to be one of the evaluation methods for the tensile characteristics of DFRCC.
121 citations
TL;DR: In this paper, X-ray diffraction (XRD)/Rietveld method was applied to analyze the hydration progress of cement paste prepared with blast furnace slag powder (BFS) and limestone powder (LSP).
Abstract: The X-ray diffraction (XRD)/Rietveld method was applied to analyze the hydration progress of cement paste prepared with blast furnace slag powder (BFS) and limestone powder (LSP). The Rietveld method can be used to quantify the amount of amorphous phase as well as crystalline phases. However, in cement paste containing BFS, two kinds of amorphous phases, unhydrated BFS and C-S-H, are included and the Rietveld method cannot distinguish them. In order to discriminate these two phases, a selective dissolution method was used to quantify the amount of unhydrated BFS. By combining these two methods, it became possible to quantify the amount of BFS and C-S-H in hydrated cement. The analysis results show that BFS accelerates the hydration of C3S, C3A, and especially C4AF. The strength increasing effect of LSP is more pronounced in the ordinary Portland cement (OPC) - BFS system than in the OPC system. This is attributed to the higher amount of calcium aluminate hydrates generated in the BFS contained system compared to the system without BFS. The additional calcium aluminate hydrates fill pores as calcium carboxaluminate by the reaction with LSP, increasing the compressive strength. These results show the effectiveness of the XRD/Rietveld method as an analysis tool for cement hydration relating to various properties of cement materials.
118 citations
TL;DR: In this paper, a self-diagnosis composite is employed as the heating device used to heat up cracked parts in the concrete and a pipe made of heat-plasticity organic film containing a repair agent is embedded in concrete.
Abstract: A fundamental study was carried out to develop a kind of smart concrete that has a self-healing system that incorporates a heating device. Self-diagnosis composite is employed as the heating device used to heat up cracked parts in the concrete. This heating device and a pipe made of heat-plasticity organic film containing a repair agent are embedded in the concrete. The film is melted through suitable heating. Selective heat around a crack can melt the film to allow the repair agent to fill up the crack and harden the repair agent in the crack. Three-dimensional thermal analysis and an experimental study were carried out to confirm the proposed method.
116 citations
TL;DR: In this article, a representation of their molecular conformation (eg worm-, brush- or star-like polymers) was developed and the amount of polymer adsorbed on cement rapidly decreases with increasing side chain length nEO.
Abstract: α-Allyl-ω-methoxypolyethylene glycol - maleic anhydride copolymers were synthesized with side chain lengths nEO from 0-130 and characterized by aqueous GPC A representation of their molecular conformation (eg worm-, brush- or star-like polymers) was developed The amount of polymer adsorbed on cement rapidly decreases with increasing side chain length nEO Zeta potential measurements using the electroacoustic method in cement paste with w/c = 05 indicate that worm-like copolymers with nEO ≤ 7 adsorb flat (“train” type) and form a densely packed, thin polymer film In this case, the adsorbed amount of copolymer is high For star polymers with nEO ≥ 34, preferred orientation of the polymer main chain is perpendicular to the cement surface (“tail” type) The result is a thick polymer layer, with a second electrochemical double layer on top For star polymers, the adsorbed amount is low because of the higher surface occupancy of horizontally layered side groups
106 citations
TL;DR: In this article, the effects of strain rates on tensile behaviors of reactive powder concrete (RPC) specimens subjected to rapid loading were investigated and a rate-dependent bridging law expressing the relation between tensile stress and crack opening was proposed.
Abstract: Reactive Powder Concrete (RPC) reinforced with short steel fibers is characterized by ultra-high strength and high fracture toughness Because of its excellent properties, RPC may be suitable as an advanced material for reinforced concrete structures subjected to impact loading Thus, the objective of this study was to find out the effects of strain rates on tensile behaviors of RPC specimens subjected to rapid loading The influence of the loading rates on failure modes, tensile stress-elongation curves and tensile stress-crack opening curves was investigated Furthermore, based on the test results, a rate-dependent bridging law expressing the relation between tensile stress and crack opening was proposed
104 citations
TL;DR: In this paper, an experimental results from tests on seven 650 mm deep large-scale reactive powder concrete (RPC) I-section girders failing in shear are reported.
Abstract: Experimental results from tests on seven 650 mm deep large-scale reactive powder concrete (RPC) I-section girders failing in shear are reported herein. The girders were cast using 150 170 MPa steel fiber RPC and were designed to assess the capacity to carry shear stresses in thin webbed prestressed beams without shear reinforcement. The tests showed that the quantity and types of fibers in the concrete mix did not significantly affect the initial shear cracking load but increasing the volume of fibers increased the failure load. A design model is developed to calculate the strength of the RPC beams tested in this study. The model is based on crack sliding and uses plasticity theory combined with observations from the variable engagement model for mode I failure of fiber reinforced concrete. The results of the model are compared with test data and show a good correlation.
100 citations
TL;DR: In this paper, experimental measurements of these processes in cement pastes and mortars with and without SRA additions are presented in light of the Kelvin equation, and the results indicate that SRAs can provide benefits in several new applications beyond their conventional usage to reduce drying shrinkage.
Abstract: Because most shrinkage-reducing admixtures (SRAs) significantly reduce the surface tension of a cement paste pore solution, they will naturally influence all physical properties and processes that are dependent in some way on surface tension. Such properties include internal relative humidity, capillary stresses, and freezing point depression, all via the Kelvin equation and its variants (Kelvin-Laplace, Gibbs-Thomson). Processes that will thus be strongly influenced by the presence of SRAs include drying, autogenous stress and strain development, and freezing. In this paper, experimental measurements of these processes in cement pastes and mortars with and without SRA additions will be presented in light of the Kelvin equation. The experimental measurements that are applied to early-age specimens include X-ray absorption measurements to quantify drying profiles, bulk mass loss measurements, measurements of internal relative humidity, assessments of autogenous deformation under sealed curing conditions, and low temperature calorimetry scans to quantify freezable water content. The results indicate that SRAs can provide benefits in several new applications beyond their conventional usage to reduce drying shrinkage.
TL;DR: In this article, the impact response of a reactive powder concrete (RPC) beam was evaluated with a drop hammer impact test and a static flexural loading test to find out the residual load carrying capacity after impact loading.
Abstract: The aim of this study was to experimentally examine the impact response of a RPC (Reactive Powder Concrete) beam and develop an analytical model to represent its impact response. Thus, a drop hammer impact test was performed to investigate the influence of drop height of the hammer on the impact response of the RPC beam. Subsequently, a static flexural loading test was conducted to find out the residual load carrying capacity of the RPC beam after impact loading. In the impact analysis, the two degrees of freedom mass-spring-damper system model was used. The analytical results were in good agreement with the experimental results when high damping for the local response at the contact point was assumed.
TL;DR: In this article, a time-dependent structural analysis method under multi actions in consideration of drying shrinkage due to moisture transfer and rebar corrosion due to chloride ions penetration as well as external load actions was developed.
Abstract: A time-dependent structural analysis method under multi actions in consideration of drying shrinkage due to moisture transfer and rebar corrosion due to chloride ions penetration as well as external load actions was developed. The Rigid-Body-Spring Networks (RBSN) model and the truss networks model were used for structural analysis and mass transfer analysis, respectively. In addition, mass transfer through bulk concrete and mass transfer through cracks by setting truss networks on the boundaries of Voronoi particles, was also considered. The developed method was confirmed to simulate well the deterioration process due to mass transfer for initial cracking behavior and ultimate behavior of concrete structures.
TL;DR: In this paper, a computational system for predicting the long-term degradation of cement hydrates due to calcium leaching is presented, where the leaching of calcium ions from hardened cement hyddrates is simulated as the multi-phase equilibrium of calcium in solid and liquid phases and their transport is formulated on the basis of thermodynamics.
Abstract: A computational system for predicting the long-term degradation of cement hydrates due to calcium leaching is presented. The leaching of calcium ions from hardened cement hydrates is simulated as the multi-phase equilibrium of calcium in solid and liquid phases and their transport is formulated on the basis of thermodynamics. The time-dependent properties of cement hydrates associated with hydration, pore-structure development, and moisture transport are evaluated by integrating calcium leaching and statistical models of chemo-physics. The proposed model delivers reasonable predictions of calcium leaching in high-performance concrete with a low water-to-cement ratio as self-curing takes place.
TL;DR: A low-stickiness type polycarboxylic acid-based superplasticizer has been developed based on the conventional PC-based SLAM as mentioned in this paper, which is faster than that with the conventional SLAM SLAM.
Abstract: This paper describes the history and new trends in the development of chemical admixtures in Japan. PC (polycarboxylic acid)-based agents are the main products in the superplasticizer market. A low-stickiness type PC-based superplasticizer has been developed based on the conventional PC-based superplasticizer. The flowing speed of concrete with low stickiness type PC-based superplasticizer is faster than that with the conventional PC-based superplasticizer. By addition of a new viscosity agent consisting of a mix of anionic and cationic surface active agents, the three dimensional reticulation structures is formed in fresh cement paste and the viscosity of the cement paste can be increased and segregation can be prevented. The hydration of cement in sludge water is controlled by addition of a set-retarder, and the specific surface area of cement does not increase while a large amount of unreacted alite remains in the sludge water. Recycling of concrete at ready mixed concrete plants is possible without adversely influencing the properties of concrete when sludge water with the set-retarder containing gluconate salt is used. The slurry type and powder type calcium aluminate based accelerator (CA) and calciumsulfoaluminate based accelerator (CSA) for shotcrete have been developed. In the case of CA, the final setting time of the mortar is accelerated by increasing the dosage. By adding of CSA, both the initial and final setting times of mortar are shortened with increased dosages.
TL;DR: In this paper, a path-dependent fatigue constitutive model for concrete tension, compression and rough crack shear is proposed and directly integrated with respect to time and deformational paths actualized in structural concrete.
Abstract: Path-dependent fatigue constitutive models for concrete tension, compression and rough crack shear are proposed and directly integrated with respect to time and deformational paths actualized in structural concrete. This approach is experimentally verified to be consistent with the fatigue life of materials and structural members under high repetition of forces. The mechanistic background of the extended truss model for fatigue design is also investigated. The coupling of fatigue loads with initial defects is simulated and its applicability is discussed as a versatile tool of performance assessment.
TL;DR: In this article, the effects of chemical structures of graft copolymer on cement-dispersing performance were investigated to elucidate the fluidizing mechanism of polycarboxylate-based superplasticizer containing graftcopolymer with polyethylene oxide graft chains.
Abstract: The effects of chemical structures of graft copolymer on cement-dispersing performance were investigated to elucidate the fluidizing mechanism of polycarboxylate-based superplasticizer containing graft copolymer with polyethylene oxide graft chains. A graft copolymer with longer graft chains showed better dispersing stability with a small amount of adsorption. The adsorption study indicated that the graft chains elongated as the adsorption density increased. The thickness of the graft chain in the copolymer that adsorbs on a cement particle also depends on the average distance between two graft copolymers and the graft chain spacing within the copolymers, depending on the geometric features of the copolymer. The modified steric stabilization model incorporating the extension of graft chains due to adsorption and the geometric restriction of the copolymer gives a useful explanation of the relationship between adsorption and the flow of paste containing different graft copolymers.
TL;DR: In this paper, an experimental investigation was carried out to generate the complete stress-strain curves of steel fibre reinforced high strength concrete under axial compression, and the effect of the mixed aspect ratio of fibres on the stressstrain behavior of steel fiber reinforced high-strength concrete was also studied by blending short and long fibres.
Abstract: An experimental investigation was carried out to generate the complete stress-strain curves of steel fibre reinforced high strength concrete under axial compression. The experimental program consisted of testing 100 x 200 mm concrete cylinders. The experimental variables of the study were concrete strength levels (58.03 MPa and 76.80 MPa), volume fractions (0.5% to 2.0%) and aspect ratios (20 and 40) of flat crimped steel fibres. The effect of the mixed aspect ratio of fibres on the stress-strain behavior of steel fibre high strength concrete was also studied by blending short and long fibres. The effects of these variables on the stress-strain curves are presented and discussed. The results indicate that high strength concrete can be made to behave in a ductile manner by the addition of suitable fibres. It is concluded that short fibres are more effective in controlling early cracking, thereby enhancing the strength of the composite, whereas long fibres are more effective in providing post peak toughness. Concrete strength seemed to have an adverse effect on the deformability of fibre reinforced high strength concrete. Based on the test data obtained, a simple model is proposed to generate the complete stress-strain relationship for steel fibre reinforced high strength concrete. The proposed model has been found to give a good representation of the actual stress-strain response.
TL;DR: In this article, a direct path-integral scheme with fatigue constitutive models for concrete tension, compression and rough crack shear is used to predict the life cycle of RC slabs.
Abstract: A direct path-integral scheme with fatigue constitutive models for concrete tension, compression and rough crack shear is used to predict the life-cycle of RC slabs. The three-dimensional fatigue analysis successfully predicts the characteristic mode of failure under moving loads as well as in the case of fixed-point pulsation in shear. Importantly, drastically shortened fatigue life under traveling wheel-type loads is mechanically demonstrated by implementing a constitutive model of cracked concrete using a direct path-integral method of fatigue damage simulation. A sensitivity study is carried out to clarify the influence of shear transfer decay and compression fatigue on RC slab performance. The effect of boundary conditions on fatigue life is also investigated.
TL;DR: In this paper, a new phenomenon has been discovered, i.e., shrinkage of loaded specimens is larger than of non-loaded ones, which is in agreement with Powers' creep theory.
Abstract: Tensile creep tests on high-strength concrete have been performed. Besides up-to-date creep data which have been generated a new phenomenon has been discovered, i. e. shrinkage of loaded specimens is larger than of non-loaded ones. It seems that this phenomenon is in agreement with Powers' creep theory.
TL;DR: In this article, the fracture mechanism of reinforcing steels in concrete structures damaged by the alkali-silica reaction (ASR) was investigated in the Kansai area in Japan.
Abstract: Instances of reinforcing steel fracture in concrete structures damaged by the alkali-silica reaction (ASR) have been discovered recently in Japan. As long as reinforcing steels are not broken due to ASR-caused expansion, the safety of a structure is considered not to be seriously compromised. However, the safety of a structure becomes questionable when the confinement of concrete becomes degraded due to the fracture of reinforcing steel bars. Therefore, it is important to clarify the mechanism of the fracture of reinforcing steel bars and develop methods for detecting steel bar fractures and strengthening concrete structures damaged by ASR.This paper describes the fracture of reinforcing steels in the case of concrete structures damaged by ASR in the Kansai area in Japan. It then introduces the results of investigation on the fracture mechanism, nondestructive testing methods, and repair and strengthening methods for damaged concrete structures.
TL;DR: In this paper, electron probe microanalysis (EPMA) has been applied for the quantitative evaluation of Cl ingress into concrete, which is useful for the estimation of the apparent Cl diffusion coefficient, Da.
Abstract: Electron probe microanalysis (EPMA) has been applied for the quantitative evaluation of Cl ingress into concrete. In order to obtain quantitative data on Cl concentration, the measurement conditions were discussed statistically in detail and sample measurement conditions were introduced. The absolute concentrations of Cl obtained through EPMA were found to be equivalent with wet analysis and the effect of matrix differences to be negligible. By using the difference in chemical composition between cement paste and aggregate measured by EPMA with a spatial resolution of 100 µm, it was possible to discriminate the paste part in concrete. Since Cl penetrates into concrete through the paste part, the Cl concentration profile obtained by EPMA is useful for the estimation of the apparent Cl diffusion coefficient, Da. The quantified value of Cl concentrations obtained with EPMA were confirmed through comparison with traditional slicing and grinding methods. Based on the measurement results, the Da value was calculated for various concrete mixtures and the results were found to be equivalent with those yielded by conventional methods.
TL;DR: In this paper, an enhanced multi-chemo-physical model for the time-dependent deformation of concrete is proposed based on thermodynamic state of moisture in micro-pores, which is divided into moisture transport through CSH gel grains and water in motion within the interparticle spaces of hydrate micro-products.
Abstract: An enhanced multi-chemo-physical model for the time-dependent deformation of concrete is proposed based on thermodynamic state of moisture in micro-pores. The moisture migration mechanism is divided into 1) moisture transport through CSH gel grains and 2) water in motion within the inter-particle spaces of hydrate micro-products. The new kinematic model makes it possible to simulate both long- and short-term concrete creep. An enhanced mechanistic law of stress path dependency is introduced to cope with a wide variety of stress and ambient histories as well. Time-dependency at elevated temperature is also investigated with current high-accuracy thermo-hygro dynamics. The instantaneous plasticity in direct connection with evaporating moisture from CSH crystal inter-layers is incorporated into the predictive system. Although some mechanisms remain unverified, drying shrinkage and creep at high temperature are fairly simulated.
TL;DR: In this article, an analytical model based on a fiber model technique for representing the behavior of a reinforced Reactive Powder Concrete (RPC) beam subjected to rapid flexural loads was developed.
Abstract: The aim of this study was to develop an analytical model based on a fiber model technique for representing the behavior of a reinforced Reactive Powder Concrete (RPC) beam subjected to rapid flexural loads. In the analytical model, first, the moment-curvature relationship of the section of the RPC beam was calculated, considering the fact that the constituent materials, i.e., RPC and reinforcing steel, exhibit strain rate effects on mechanical properties. Then, the load-midspan deflection relationship was obtained through the moment-curvature relationship. The analytical model was applied to the experimental results for verification. The analytical results were in good agreement with the experimental results. Subsequently, analytical investigations were performed to find out the influence of variables, such as loading rates, compressive strengths, the amount of reinforcing steel and the volume fraction of steel fibers, on the behaviors of RPC beams.
TL;DR: In this paper, the authors examined the influence of surface tension of immersion liquid on static and fatigue strength of concrete, and found that the larger the surface tension, the smaller the static and fatigues of concrete.
Abstract: To clarify the compressive static and fatigue strength of concrete immersed in various liquids, experimental studies were conducted. The influence of the surface tension of immersion liquid on static and fatigue strength of concrete were examined based on the knowledge that (1) the fracture process of concrete at the macro scale is the result of generation and propagation of internal microcracks, (2) strain energy is partially released as surface energy when microcracks are formed, and (3) the magnitude of the surface energy between a solid and a liquid is affected by the surface tension of the liquid. The results indicate that the larger the surface tension of the immersion liquid, the smaller the static and fatigue strength of concrete, and that these are characterized by a linear relationship. It also became clear that the fatigue of concrete in air hardly matters whereas special attention should be given to the fatigue of concrete in the case of concrete structures that are frequently immersed in liquid with a larger surface tension than water, such as marine structures.
TL;DR: In this paper, the deformation capacity and energy dissipation of rectangular columns with corner deformed bars lap-spliced at floor level through RC jacketing or CFRP wrapping was investigated.
Abstract: Seismic rehabilitation of rectangular columns with corner deformed bars lap-spliced at floor level through RC jacketing or CFRP wrapping, is experimentally studied In three unretrofitted columns, deformation capacity and energy dissipation drop fast with lap length below 45-bar diameter Three columns were cyclically tested after concrete jacketing of their full length and another nine after CFRP wrapping of the lap splice and plastic hinge region Five CFRP layers were found to be more effective than two, but the improvement was not major The positive effect of FRP wrapping on flexural resistance, ultimate deformation and energy dissipation declined with decreasing lap length There is a limit to the improvement that can be obtained through FRP wrapping: if lapping is as short as 15-bar diameter, its adverse effects on force capacity and energy dissipation cannot be sufficiently removed by FRP wrapping Overall, RC jacketing is more effective than FRP wrapping for the improvement of the deformation capacity of columns with 15-bar diameter lapping
TL;DR: In this paper, the deformation properties of superplasticized concrete are discussed from the viewpoint of fundamental mechanisms, i.e., proportional correlation of the adsorption amount of super-plasticizer per surface area of hydrate to the fluidity.
Abstract: To achieve durable concrete structures, the first important step is the sound placing of concrete. Compatibility among concrete materials, an important issue for controlling the workability of concrete for sound placing, has been the object of much attention over the past decade. Every engineer wants to have reliable methods to examine the fluidity performance of cement and superplasticizers. In this study, the way to examine fluidity performance is discussed from the viewpoint of fundamental mechanisms. One important point is the deforming properties of superplasticized concrete. When fresh concrete deforms homogeneously, the workability of concrete mixtures can be explained by one basic theory of superplasticizer, i.e. proportional correlation of the adsorption amount of superplasticizer per surface area of hydrate to the fluidity. Moreover, the examination of the fluidity performance of cement and superplasticizers should consider the condition of real concrete with respect to the water-to-cement ratio and mixing procedure of materials.
TL;DR: In this paper, the authors proposed constitutive models based on basic test results for shear failure behavior of high-performance fiber reinforced cement composites (HPFRCC), which match reasonably well the experimental results of HPFRCC structural elements.
Abstract: High-performance fiber reinforced cement composites (HPFRCC) are highly ductile and characterized by pseudo strain hardening in tension. High-level in structural performance through the application of HPFRCC is expected. However, many uncertainties remain regarding the influence of the tensile characteristic of HPFRCC on the shear resistance mechanism of structural elements utilizing HPFRCC. Though FEM analysis is an effective engineering tool to analyze the relationship between the material characteristics and the structural performance of elements, a robust constitutive model is indispensable for obtaining accurate results. This paper proposes constitutive models based on basic test results. The proprieties of the model are confirmed based on a comparison between the analytical simulation and the structural test results for shear failure behavior. The analytical results using the proposed model match reasonably well the experimental results of HPFRCC structural elements.
TL;DR: In this article, the application of a High Performance Fiber Reinforced Cementitious composite (HPFRCC) short column reinforced with steel bars was introduced for damage mitigation against large earthquakes, which has very high strength, stiffness and ductility compared with conventional RC columns with the same configuration and bar arrangement.
Abstract: It is essential to introduce performance-based design systems and develop new technologies for meeting the social requirements of building structures. This paper begins by discussing the need for damage mitigation for building structures under performance-based design. Based on this concept, the application of a High Performance Fiber Reinforced Cementitious composite (HPFRCC) device is introduced. This device is a HPFRCC short column reinforced with steel bars that has very high strength, stiffness and ductility compared with conventional RC columns with the same configuration and bar arrangement. An analytical study on the seismic response of a soft first story building with and without such HPFRCC devices was performed as a case study to investigate the feasibility of the proposed technique for damage mitigation against large earthquakes. The results indicate that HPFRCC devices can reduce the drift angle of the soft first story from 2% to 0.5% in the case of seismic input with maximum velocity normalized at 50 cm/s. Since a drift angle of 0.5% means an elastic response of the structure, HPFRCC devices are confirmed to have significant potential as a new structural technology for damage mitigation.
TL;DR: In this paper, a transient nonlinear analysis is proposed as a way of predicting the long-term deformation of cracked reinforced concrete and a mechanistic creep constitutive model for post-cracking tension-stiffness is presented.
Abstract: Transient nonlinear analysis is proposed as a way of predicting the long-term deformation of cracked reinforced concrete and a mechanistic creep constitutive model for post-cracking tension-stiffness is presented. The effect of drying shrinkage is integrated into the predictive scheme using the thermo-hydro physics of porous media, and a simple equivalent method of analysis is discussed for the practical performance assessment of structural concrete. Careful verification of the model is carried out with respect to the creep deflection of RC beams and slabs subjected to multi-axial flexure. Three-dimensional fiber and plate & shell elements are used for the space discretization of the analysis domain.