In this study, discrete crack formulation for cracking in concrete was proposed and its fundamental characteristics was investigated. Crack was expressed as the isoparametric quadratic linear element and it was modeled by the contact element between concrete elements. A crack element was inserted at the point, where the maximum principal tensile stress occurred, and to the direction perpendicular to it. The proposed crack element was distinguished by the tension softening curve and the fracture energy, which were based on the non-linear relationship between transferring stress and crack opening. The analytical study on a plain concrete beam was carried out. The crack propagation analysis of a plain concrete beam was carried out by the use of the finite element method.

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In order to clarify the durability performance of cement composites, it is necessary to simulate mass transport properties, and in this case, it is important to take into consideration the heterogeneity of the hardened cement. In this research, the connectivity of transition zone, which is effective factor for mass transport properties, was expressed by the “burning algorithm”. As a result, the sand amount that brings about the rapid increase in the connectivity depends on water cement ratio. And using the coefficient of mass transport and percolation theory. we simulate the mass transport properties in 3-D. Comparing the analytical results with experimental results, this simulation may be effective to evaluate the real condition of mass transport properties.

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We experimented with RC members which had limited to shear crack position with notch to estimate shear strength of RC members with fiber sheets. In these experiments, we investigated effective bond area of fiber sheets which contributed to shear strength. It is possible to estimate the improvement of the RC member with the fiber sheets by applying effective bond area to the equation of bond strength between the fiber sheet of the research by which we reported. Moreover, we investigated the effect of shear strengthening of RC beams with fiber sheets and the effect of prestressed force introduced into a part of fiber sheets. As results of these experiments, the effect of shear strengthening by fiber sheets and prestressed force was clarified. Moreover, the experiment value can be estimated by the calculation.

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Corrosion protection of reinforced concrete members with zinc-coated steel fibers was evaluated among the corrosion-protection methods against chloride-induced deterioration. Role of zinc-coated galvanized steel fibers in severe environment was confirmed as a sacrificial anode for embedded steel in an electrochemical reaction due to diffusion of chloride ion.
Modified test of ferroxyl transparent gel and accelerated corrosion test were applied to investigate the corrosion-protection behavior of embedded steel bars in the galvanized steel fiber reinforced concrete. Hydrogen evolution problem due to galvanized steel fibers in a high alkaline environment was discussed and the method of control the evolution was proposed.

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In the aseismic design of liquid storage tanks an assumption that the tank wall is a rigid body has conventionally been made. However, since the size of liquid storage tanks becomes larger, the dynamic rigidity comparatively decreases and it is necessary to include deformations of the tank walls in the design of tanks. In this study, a numerical method was developed for Axi-Symmetric analysis of tank structures including hydrodynamic and foundation interaction effects. The finite element method was newly developed for the internal liquid based on the velocity potential theory. In order to absorb the radiation wave energy through the boundary, a viscous boundary has been employed. Validity and utility of the program are demonstrated by some test calculations including those for a tank made of concrete.

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Several damaged footings with cracks on their upper face were found after the Hanshin-Awaji Earthquake. To investigate the failure mechanism and the bearing capacity of the footings, 1/2 scale tests were performed using models simulating such damage. Accoring to the test results, ultimate strength was 106 tf, which is 2.0 times larger than the design load, and it had a relatively high ductility factor of 7. The failure mechanism of the tested specimen was similar to those of damaged footings, and this cracking might be caused by the concentrated tensile stress at the corner where the footing and column intersected.

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This paper describes a nondestructive method to evaluate the size and depth of interfacial defects between the concrete members and the enclosing steel plate by the infrared thermographic technique. In this procedure, in order to investigate the influence of a defect in a thermography, liquid nitrogen is used to cool the surface of the steel plate. Its thermal distribution are measured. From these measurements, it is possible to estimate the diameter of circular defects from the calculated inflection points in the thermal distribution curve. The process to evaluate the depth of the defects by using the relation between the volume of the defects and proposed thermal parameters is also presented.

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In this study, the strength development of mortar specimens incorporating limestone powder is investigated varying the source, the specific surface area, and the dosage of limestone powder. The experimental results demonstrate that concrete incorporating limestone powder remarkably improves the strength development at low curing temperature. The effect of improving the strength development by limestone powder greatly depends on the specific surface area and the dosage of limestone powder. Finally, it is concluded that the mechanisms of the strength development by limestone powder are mainly based on contributing the surface of limestone powder to the site for forming C-S-H and the filler effects to macro pores in capillary pores.

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The purpose of this study is to reveal the strength development of self-compacting concrete incorporating ground granulated blast-furnace slag (ggbs) constructed in cold weather conditions. First of all, using mortar specimens varying the fineness of ggbs and the replacement level of ggbs, the strength development for various curing methods and curing temperatures is researched. Then the application of heat curing necessary for improving an early strength development at low temperatures is investigated. Finally, considering the change of season at construction site from winter to spring, the properties of strength recovery of self-compacting concrete incorporating ggbs caused by the rise of temperature are discussed.

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Delamination between FRP sheets and concrete, which might be caused by inappropriate works or deterioration due to a time elapse, decreases bond strength between FRP sheets and concrete, and also decreases the strength of the structural element reinforced with FRP sheets. Therefore, these defects must be accurately detected and be properly repaired. This paper concerns the detection of defects between FRP sheets and concrete by measuring thermal distribution of the surface using an infrared thermography method. It is confirmed from the basic experiments using heated or cooled specimens that the detection of defects is influenced by the type and number of FRP sheets, as well as the thickness of defects. It is shown from experiments in the open air that defects can be detected from the difference between specimens and circumferential air in both clear and cloudy weather. Moreover, a non-steady heat transfer analysis by FEM is conducted and it is confirmed that the analysis can well simulate the experimental results.

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The pipe-cooling system is one of the major methods that are used to control thermal stress of massive concrete. In this study, three-dimensional finite element method to consider the heat balance between concrete at the surface of cooling pipe and water in cooling pipe is proposed. The results of this theoretical analysis are agreed on the measurements of temperature in each point of water temperature in the pipe and concrete temperature at the surface of cooling pipe and around the cooling pipe. Therefore, this theoretical method is made clear to be one of the methods to estimate the effect of heat elimination applicably by the cooling pipe system.

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A fundamental study on fracture mechanisms of concrete-piles under both cyclic and monotonic loadings is performed by using acoustic emission techniques. Full-scale prestressed high-strength concrete piles are subjected to bending and shear loadings. Growth of cracks is monitored by AE, and three-dimensional AE source location is conducted together with identification of crack. These results are compared with results of the pile integrity tests (PIT) and visual observation. It leads to the conclusion that damage inspection by AE is more effective than by PIT in the case where open cracks due to loading would close under unloading. The crack widths evaluated by AE were remarkably compatible to the results of the wave velocity test.

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One comprehensive numerical system is proposed for the attempt to solve the problem related to deterioration of reinforced concrete (RC) structures under chloride-induced corrosion. This numerical system is characterized by combining the physico-chemical models related to the migration of corrosion-related substances in concrete, such as chloride, oxygen and moisture, and the electrochemical models dealing with the formation of natural potential and corrosion current of RC members under chloride-induced corrosion. Experimental comparison indicated the availability of this numerical system on modeling corrosion of steel in concrete structures under chloride attack.

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