In this paper, the results of the experiments that were performed to clear the fatigue properties of concrete and to improve the fatigue strength were considered. Also, the microstructure of concrete subjected to cyclic loading was investigated. The following conclusions were obtained: 1) The fatigue strength of submerged concrete is less than that of dried concrete. 2) The fatigue strength is slightly improved by the strengthening of the transition zone. 3) The damage of dried concrete occurs in the transition zone from the early cycle and gradually increases to the failure. 4) Under the submerged condition, the damage of the transition zone is small until before the failure, and the damage rapidly increases just before the failure and then the concrete fails.

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In this study, the conventional relation between K-value and elastic modulus of the Boussinesq's foundation examined from the FEM analysis and the results of the static loading test for concrete pavements conducted at the Public Works Research Institute from 1997 to 1998. From results of the examination, it was found that to obtain the bending stress of concrete slab, a factor of 1.50 must be applied to the coefficient of Vesic's conversion equation.

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Based on the experience obtained from the Hyogo-Ken Nambu 1995 earthquake, a reduction in residual displacements is necessary to achieve seismic resistant bridges. The objective of this study is to investigate the effectiveness of partially prestressed concrete (hereafter PPC) to reduce residual displacements of bridge piers. A series of experiments was carried out using small-scaled pier specimens. The experimental program basically showed an effectiveness of using PPC to reduce residual displacements after earthquake excitations. Additionally, a new hysteretic restoring force model for PPC piers was proposed and its applicability was verified. Furthermore, inelas tic residual drift ratio spectrums were introduced for piers having different quantities of prestressing tendons.

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This paper attempts to clarify the failure mechanism of FRP rods used as concrete reinforcement, and proposes a creep simulation model based on failure statistics of each component of FRP rods, such as faibers and matrix rein. FRP rods, made of aramid, glass, or carbon fibers were used. In order to examine the adequacy of the simulation model, the calculation results were compared to experimental data. As a result, it was determined that the proposed simulation method could be used to evaluate static strength, creep failure time, and creep strain of FRP rods quantitatively.

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The analytical model for creep mechanism of concrete as a porous permeable material was established. In the analytical mode, the diffusion phenomenon and seepage phenomenon for pore water were introduced in detail and then the model was expanded so as to be able to be taken the visco-elastic behavior of pore water and cement paste into account. The effect of water migration on the creep phenomenon was estimated due to the analytical and experimental study. Moreover, the degree of water migration behavior effect and visco-elastic behavior effect of cement paste on the creep phenomenon was estimated due to the analytical and experimental study and then the creep mechanism was probed.

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Recently the use of carbon fiber sheet (CFS) to strengthen and rehabilitate existing reinforced concrete has increased. Reinforced concrete member strengthened with CFS is different from reinforced concrete member without strengthening in failure characteristics, because bond mechanism of CFS is different from that of reinforcing bar. In this study, bond characteristics of is CFS clarified, and it is indicated that tension stiffness of CFS is a principal factor which influences effectiveness of strengthening. Moreover, “multi-layering anchorage system”, in which CFS is multi-layered on the only end of adhesion area, is proposed to develop maximum load.

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High strength concrete and high strength reinforcing steel have been put into practical of prestressed concrete use at present. However high strength prestressing steel has been developed, but the prestressing steel has not been still in use. This paper presents the results of flexural test of the prestressed concrete beams using high strength prestressing steel and concrete with several strength includes 100MPa grade high strength concrete. Furthermore a trial calculation using fiber model method was made and the prestress strength applied high strength concrete beams with high strength prestressing steel was considered.

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Fly ash-Cement mixture mixed at low water content close to optimum moisture content is only wet powder immediately after mixing. After going through vibration compaction for a few minutes the wet powder becomes fluidized and can be sufficiently compacted. By applying this fluidized phenomenon for manufacturing, water to powder ratio and cement content can be reduced. So quality and cost efficiency of high fly ash concrete can be improved.
In this study the authors investigated the method of mixture design and quality control of high fly ash concrete. From the investigation, it was found that the optimum mixture can be determined by the flow tests of fly ash and quality of high fly ash concrete can be controlled by the fluidization time.

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To assess properly the crashworthiness and the safety of the RC structures subjected to impact/impulsive loads, it is important to find precisely the dynamic mechanical properties of the concrete materials. Over the last two decades many studies have been undertaken on the behavior of the concrete under uniaxial rapid loading. However, the actual concrete material within the RC structures may be generally under triaxial stress states due to the complex loadings and the confining effect of the transverse reinforcement. Thus, the apparatus for testing concrete under the triaxial rapid compressive stress states was newly developed in this study. This study is to investigate the behavior of concrete material subjected to high strain-rate and triaxial stress. The compressive strength of specimen, the confining pressure and the loading rate are chosen as test parameters. From test results, the effects of these parameters on the mechanical properties of concrete material are examined. Furthermore, based on the concept of the equivalent uniaxial strain, the orthotropic constitutive model with the strain-rate effects is proposed

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The strain softening behaviors of concrete material under uniaxial tensile rapid loading has been left unsolved experimentally. It may be the reason that it is difficult to measure the post-peak behaviors of plain concrete since the fracture of the test specimen will happen suddenly and instantaneously under rapid loading. Thus, the new testing method for measuring dynamic tensile softening behaviors of concrete is proposed in this study. Also, this study is to investigate the strain softening behaviors of concrete material in tension under rapid loading. The loading-rate is chosen as test parameter. From tests results, the effect of the loading-rate on the tensile softening behaviors of concrete materials is examined. Furthermore, based on the fictitious crack model, the constitutive model for the uniaxial tensile rapid loading is presented.

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The concrete material of RC structures may be under triaxial stress states due to complex loadings and the confining effect of transverse reinforcement. Thus, to assess properly the crashworthiness and the safety of the RC structures subjected to impact/impulsive loads, it is important to find precisely the dynamic mechanical properties of concrete materials under triaxial compressive stress states. This study is to investigate the dynamic strain softening behaviors of concrete material subjected to high-strain rate and triaxial stresses. The compressive strength of specimen, the confining pressure and the loading rate are chosen as test parameters. From test results, the effects of these parameters on the strain softening behaviors and strain localization are examined. In consideration of test results, a set of formulations of the axial compressive stress-axial compressive strain in the fracture zone is proposed.

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In this study, test results of 12 prestressed concrete beams without shear reinforcement and 12 prestressed reinforced concrete beams are used in order to evaluate the effects of prestress level and prestress distribution across the section on shear capacity. Shear force carried by concrete is calculated according to JSCE code, ACI code and the modified compression field theory, and so on. Those values are compared with the experimental results. From these results, a simple method, which considers the effect of prestress including stress distribution across the section as well as the inclination of diagonal crack on shear capacity, is proposed.

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The proof strength of concrete structures decreases due to corrosion of reinforcing steel. The relationship between crack width and amount of reinforcing steel corrosion is an important parameter in maintenance and management of the concrete structures. In this paper, basic calculation formulation was derived using cylinder model. A smeared crack model was used to evaluate the crack mode due to reinforcing steel corrosion. Crack generation and progression, crack location and number of cracks were analyzed. Then, the relationship between crack width and amount of reinforcing steel corrosion was calculated using a discrete crack model.
In this study, crack generation position and number of cracks can be determined by using the smeared crack model. The relationship between crack width and amount of reinforcing steel corrosion can be obtained using the discrete model and calculation formulation corrected.

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Recently, early deterioration of concrete structure has caused many serious troubles. Chloride induced corrosion of reinforcing steel, that is an electrochemical reaction, is a typical cause of such deterioration. Although polarization resistance method is considered effective for monitoring corrosion in reinforcing steel, it is still difficult to determine the exact amount of corrosion loss.
In this study, characteristics of the double rectangular pulse method and the AC impedance method are investigated, and quantitative estimates of corrosion loss of reinforcing steel are accomplished, even in the case where macro-cell corrosion occurs, in which corrosion progresses at different speeds in a same steel bar.

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The objective of this study is to evaluate non-uniform quality of materials achieved in RC structures. In order to quantify the influences of structural size, reinforcement arrangement, slump value, and construction methods on the segregation, RC column and beam were made. As a material parameter showing the segregation, porosity of core specimens picked up from structures were measured. By using multiple regression analysis, the authors proposed a simple method that can evaluate the influence of each factor on the segregation and can give the non-uniform quality of materials achieved in RC structures. For applying the obtained test results to the evaluation of long-term durability performance, accelerated carbonation test and comparison the test results with durability index proposed by JSCE were also examined. From these studies, it was shown that the proposed method can be used for the quantitative evaluation of material qualities in RC structures and durability performances.

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The influence of surface properties and specimen size on the flexural failure of concrete beams repaired by crack injection techniques is evaluated by using tension softening diagrams and fracture energy. Fracture energy is an effective index to evaluate the differences in fracture behavior between rough and smooth repair surfaces. The size effect on the flexural strength of repaired specimens is larger than that of plain concrete. In addition, weak boundary layers adjacent to the repair surface adversely affect the cracking behavior of repaired specimens.

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Full-scale flexural reinforced concrete columns with cross sectional dimension of 2400mm were tested under quasistatic cyclic lateral loading in the laboratory. To determine the size effect on column inelastic behavior, a 1/4-scale replicate model was also loaded for comparison with the full-scale column behavior. Observed strains of transverse steel on compression flange side indicated that larger dimension of column section caused poorer restraint of buckling of longitudinal reinforcement. Experimental curvature profiles showed that plastic curvature in the replicate model developed up to a little higher section than the full-scale column, which might be caused by the difference of theoretical buckling length of londitudinal reinforcement. Furthermore, it was found that the base rotation induced by the strain penetration effect was different between the full-scale and replicate columns due to deterioration of the bond stress of footing concrete around post-yield longitudinal reinforcement.

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Exradosed bridges are recently increasing as a suitable bridge type between cable stayed bridges and box girder bridges, and the past tower height of exradosed bridges with three spans have been restricted under 10 to 15 meter. On the other hand, two span bridges supported by both ends have better precondition on stress fluctuation and displacement. It means that structural parts can be downsized with increasing tower heights. In this study, we analyzed characteristics of three main parts (tower, girder, cable) and tried to optimize a structural system. As a result, we found that the most suitable tower height is about 25-30 meter, which is twice of the past examples. This result was confirmed through a construction, and shows a new approach to bridge structures.

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A prediction model using a neural network and discriminant analysis to predict pavement freezing after three hours is proposed to increase the efficiency of anti-icing programs. The results of the present study revealed that the pavement freezing in three hours can be predicted with considerable precision by combining the pavement surface temperature prediction model and the detection model of pavement wetness.

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The indented type and hooked type steel fibers were selected for roller compacted concrete for pavements. The appropriate unit water content, sand percentage, reinforcement amount were found out, and water reduction degree by incorporating superplasticizer and its appropriate adding percentage by cement content were chosen for a given consistency which was evaluated by the vibrating compaction value measured by a Swedish-type Vebe apparatus. The segregation degree was reduced by using steel fiber, and the fiber angle in the concrete tended to approach the horizontal angle by compaction used surface vibrator. The flexural strength, ductility and frost resistance were improved, and bond strength between the concrete and abraised asphalt pavement surface was evaluated at the age of 7 days. The drying shrinkage was almost the same as the non-fiber roller compacted concrete regardless of increase in the unit water content for a given consistency.

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Using sand of proper quality for the bedding and joint is important, to maintain the performance of interlocking (IL) blocks on roadway. A field test using actual vehicles started in FY1997 at the PWRI, to evaluate the durability of bedding sand for roadway. Natural sand performed the best of tested materials. Using resin to fix sand caused severe breakage of blocks or loss of joint sand. It also was found that to prevent the loss of joint sand, materials whose properties are similar to those of bedding sand are desirable. Our tests lead us to propose that to evaluate the quality of bedding sand used with IL blocks on roadway, resistance against finning should be tested by impact compaction.

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This paper aims to investigate the influence of pre-cracks on the behavior of reinforced concrete beam in shear. For real RC members under severe environments, these pre-cracks are sometimes inevitable. For this purpose, an experimental program was implemented. Experimental results demonstrated significant difference between pre-cracked and non pre-cracked beams. It is found that pre-cracked beam can reach much higher capacity. Moreover, substantial difference in failure characteristics and load-displacement relationship was also discerned. Rationale in fundamental mechanics exists, that can explain the behavior of pre-cracked beam

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Recent experiments on pre-cracked beam conducted by the authors pose challenge to the numerical analysis in the field of reinforced concrete mechanics. The numerical requirements of pre-cracked beam problem are identified as (1) multi-step loading paths and path-dependency transfer, (2) multidirectional cracks with crack interaction and (3) highly anisotropic shear along pre-crack plane. Four-way fixed crack approach is judged to fulfil the above numerical requirements. The finite element analysis of pre-cracked beam is conducted. It is verified that the four-way fixed crack approach can reliably reproduce the experimental results of pre-cracked beam

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An experimental program has been conducted in order to examine the failure mechanism and localization effect of concrete subjected to uniaxial compression by measuring the distribution of local vertical strain inside a concrete specimen. The new quantitative approach of localized compressive fracture length has been presented. By considering the geometrical parameters and the properties of concrete used, it has been found that, when localization occurs, the localized compressive fracture length depends only on the size of the cross-section of the specimen. The new definition of fracture energy in compression in terms of externally applied energy per unit fracture volume has also been introduced.

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