This paper proposes an analytical model for determining the fracture load of concrete structures whose deformation and fracture behaviors are governed by occurring and growing cracks. The proposed model computes the evolution of crack, by considering the localization of cracking in brittle materials such as concrete. Furthermore, by modeling the relationship between stress transmitted to cracked surfaces and crack opening width, it is possible to follow up also the crack evolution under composite stresses. Analytical study on the previous reinforced concrete experiments using the proposed model has demonstrated that the model is capable of determining the shear strength of reinforced concrete beams which undergo diagonal tensile fracture.

View full abstract

Conventional design procedures entail determining the structural dimensions, sectional con-figuration, and materials by linear static analysis. For heavily loaded spherical shell structures, such as domed roofs, however, it is also necessary to evaluate the structural stability. Buckling analysis has been carried out on the concrete domes to evaluate their structural stabilitry.

View full abstract

In the seismic strengthening of existing reinforced concrete bridge piers with use of carbon fiber shees (CFS), it is essential to evaluate the confinement effect of the concrete by the CFS. Since there must exist the lateral hoops in the columns, it is required to evaluate the interaction between the CFS and the hoop on the confinement effect. A series of uniaxial loading test was conducted for concrete cylinders confined by the hoops and the CFS. The interaction effect is analyzed based on the test results, and a stress-strain model of concrete confined by both CFS and the hoops is proposed.

View full abstract

The problem of thermal cracks in the mass concrete caused by the heat of the cement hydration has frequently been discussed. In the present paper, heat transfer, thermal stress and thermal cracking are simulated by the 2-D finite element method. By introducing the smeared crack model and the stochastic field for the mechanical properties of concrete, the more realistic behavior of thermal tensile cracks is reproduced in the proposed analysis.
Moreover, by means of FEM-Based Monte-Carlo Simulation, the relationships between the thermal crack index and probability of occurrence of cracks and crack opening width are identified.

View full abstract

For the development of next-generation general-purpose concrete with super-durability, extensive studies were conducted on basic properties of concrete using modified grading and mineral composition of belite-based cement. The results showed that such modification makes possible the production of concrete with a wide range of performance and which completely differs from conventional types. Highly pulverized belite-based cement has excellent properties in initial and long-term strength and is thought to have great potential for the production of high-performance concrete with long-term durability.

View full abstract

To evaluate the shear strength of RC bridge piers, comparison of analytical results using modified compression field theory and experimental results which applied the horizontal load to the real RC column and 1/3 scale large specimens, was performed. The analytical results coincides relatively well with the experimental results, and it is also shown that the concrete shear strength reduces after main reinforcing bars reaches the yield strength. The parametric studies show that the increase in hoop ties leads to high crack inclination and then 45° -truss analogy over-estimates the shear resistance carried by hoop ties.

View full abstract

In the PC precast segmental beams using external cable method, the longitudinal reinforcements are not fixed continuously. Therefore, the deformations are concentrating only at the joints. This is the major difference in behavior compared to normal concrete structures. To clarify the influence due to deformation of the joint on the PC precast segmental beams, an experimental study was carried out, and also supplemented by an analytical approach and comparison was made with the experimental result. As a result using the analytical approach, both the experimental and analytical data agreed well on the flexural behavior till ultimate failure. Moreover, computation equations were proposed using the numerical method on span/depth ratio, loading system, dimension of segment, location of deviator and strength of concrete.

View full abstract

A vertical shaft of the shield tunneling method requires a bearing pile-wall to resist earth pressure at excavation. Then, the part of the pile-wall should be cut at proceeding a shield tunnel. Therefore, the most desirable material property of the shaft is a sufficient resistance against bending moment, and is also easiness to be cut by shear force. For this purpose the authors have developed a hybrid member which consists of a fiber reinforced foamed urethane (FFU) member and a reinforced concrete member. The key of the hybrid member lies in the way how to connect both members. The authors initially proposed three connection methods, such as a mechanical connection, an anchor connection and a flare welding connection. The mechanical behaviors of these three connections were examined experimentally and the anchor connection was found out as the most desirable connection. Finally, the full scale model was tested and was proved to be sufficient for actual use.

View full abstract

Due to rebound from the wall when shooting, the quality of shotcrete varies between before and after shooting. So accurate quantitative evaluation method of quality evaluation is strongly needed above all for the more demand of high quality shotcrete in the near future. From the past many experimental researches or constructional showings on shotcreting, it is empirically said that rebound is caused by various material and constructional factors, but little is clarified about its mechanism as things are. In this paper, the first theoretical approach is attempted; namely, 2-Dimensional Distinct Element Method (2D-DEM) is applied to estimate the amount of rebound. Some parametric studies are employed and the relationship between every parameters and rebound ratio is considered. As a result, application of this new method is verified against the result of our past experiment or general mentions about shotcrete rebound.

View full abstract

Nowadays, early age deterioration of concrete to be caused by chloride attack has become a severe problem. Desalination, which is an electrochemical treatment of chloride extraction from concrete, has been developed as an essential repair method. Steel bar embedded concrete acts as a cathodic electrode through Desalination process and its potential is lower than hydrogen occuring potential by electrolysis. Therefore, considering hydrogen embrittlement of prestressing steel tendons, Desalination does not yet apply prestressed concrete. In this study, hydrogen stored in prestressing steel tendons and fracture surface of its steel were investigated while Desalination to be applied prestressed concrete.

View full abstract

The purpose of this research is to present a practicable mix design method of high fluidity concrete containing a viscous agent. In this report, we arranged the mix proportion data (26 data) applied to the various executions and the real size model experiments. With the knowledge these data, and the data obtained from indoor experiments, a method was given for the mix design.
In addition, the examples of actually mix design of the high fluidity concrete containing a viscous agent, which were designed according to the method shown by this report, were described.

View full abstract

Three RC slabs were cut out from an existing composite girder bridge used for about 24 years. The two slabs among them were devoted to fatigue test using a wheel tracking machine with a pneumatic tire in a laboratory, and the remaining one slab was devoted to statically loading test. The fatigue test was carried out under a constant load of 11tf, 13tf, and 15tf respectively, and one slab collapsed in punching shear mode at 30×10⁴ in the total repetition of wheel tracking. On the other hand, the statically loading capacity of the slab was found about 79tf in punching shear mode. Based on the data obtained here and referring the past studies on similar problems, a relationship between damage degrees of the slab and the repetition of wheel tracking was discussed. The vertical shear slip on cracked sections of the slab was found an important factor as damage index in addition to deflection, crack density and crack width.

View full abstract

Many RC structures were damaged in the event of Hyogo-Nanbu Earthquake due to the malfunction of anchorage for the hoop reinforcement. It would be rather difficult to construct anchorage along with the design and construction specification of JSCE. Thus, lap joints and right-angle hooks have been found in many cases. As to the hooks, structural stability can not be clarified after peeling off of cover concrete. On the other side, RC columns tend to be influenced of bi-axial bending in the event of earthquake. When square sections have load reversal and bi-axial bending, concrete in their corners is collapsed and there is possibility of decreasing strength as hoop even through sharp-angle hook is employed. This study describes new type of anchorage by use of pins for conventional lap joints and right-angle hooks. According to the test results, it is clarified that even if the lap joints or right-angle hooks are applied to the anchorage of hoop, the concrete columns behavior is more ductile with this new reinforcing method.

View full abstract

Although the safety of a structure can be quantitatively evaluated based on reliability design, it depends on the evaluation method oneself. So we proposed the evaluation method for a safety of the structural system considering correlation between structural variables and evaluated a safety of RC bridge pier under big earthquakes considering the correlation to clarify its influence. The results showed that when the limit state affected by the correlation is controlling a safety of the structural system, a safety of RC bridge pier is raised by considering correlation in case of low safety. Furthermore, significant considerations about seismic design of RC structures were pointed out on the basis of the proposed new method.

View full abstract

Finite element analyses of RC beams, those failure modes are shear failure, are performed using rotating crack model and considering both fracture energies for tension and compression sides. As the results, although rotating crack model can not simulate diagonal tension crack perfectly, shear behavior of RC beam without shear reinforcement is captured regardless of failure modes, element size dependence in a numerical analysis is reduced owing to fracture energies and size effect of shear strength is simulated by the analysis. The analysis tends to underestimate an effect of shear reinforcement.

View full abstract

Effects of the stress-strength ratio, loaded age, and temperature in curing and loading on the tensile creep in early age concrete have been investigated in this study. The effect of the stress strength ratio was significant and its relationship with creep strain could be described by an exponential equation. The loaded age influenced only the results of loading at 1day, but little effect was observed in other loaded ages. Although the effect of curing temperature and loading period could be assessed by equivalent periods of hydration, temperature effect during loading was much significant. Since activation energy was calculated 83.7k/mol, modified equivalent periods of hydration based on the value as demonstrated was compared with experimental results. The creep model with Voigt rehological elements was presented and demonstrated to predict creep strain on varied loading pattern and temperature change.

View full abstract

This paper presents both experimental and analytical studies on the effects of steel jacket reinforcement of concrete column specimen under impulsive vertical load. First, the impact push-up tests were performed for concrete column with steel jacket and rebar reinforcement. Second, the occurrence mechanism of circumferential crack of concrete column is investigated by using a single-degree of freedom model. Third, a two dimensional finite element method (FEM) is developed in order to examine the effects of steel jacket reinforcement of concrete column. The numerical results are confirmed in good agreement with the experimental ones. Finally, the effects of reinforcement length of steel jacket are examined by using the concrete strain distributions.

View full abstract

Air permeability of joint between new and old concrete under tensile stress is investigated with mechanical properties of joint experimentally. Treatment roughening the joint surface is made by shot blast method and green cut method. Static, sustained and repeated tensile stresses are applied to specimen, respectively. When viewed in terms of the increasing ratio of air permeability coefficient of specimen in loaded condition to that of specimen in unloaded condition, the increasing ratio for joint is larger compared to that for concrete without joint. Changes in air permeability coefficient and elastic modulus of joint subjected to repeated tensile stress are related to each other by defect rate.

View full abstract

In this study, the evaluation of the compressive strength and the strength distribution of concrete deteriorated is attempted by needle penetration test. A steel needle is penetrated on the side surface of core sample pulled out of concrete structure and the relationship between load acting to the needle and the amount of penetration is measured. As the expenmental result, the compressive strength and the strength distribution of concrete can be evaluated by the relationship between load and the amount of penetration. Further, the shape of needle suitable for this testing method and the automatization of the needle penetration testing device are investigated. Based on these experimental results, It is concluded that this testing method can be applied to evaluating the deterioration of concrete structures.

View full abstract

The experimental and analytical study on the detailed estimation of the fracture energy of concrete as a porous permeable material, which is partially saturated with water, was performed. In the analytical estimation, at first, the coupled model with water and concrete solid in which the fracture mechanics was introduced was developed and then the analytical estimation for the fracture energy, which is, defined the effective stress considering the effect of pore water pressure was performed. In the experimental estimation, the effect of pore water pressure on the fracture pattern of concrete was estimated and then the experimental estimation for the fracture energy of concrete in which the pore water pressure occur was performed.

View full abstract

An examination was made of a method of forecasting pavement surface temperatures by the neural network computing system. The neuro-model can be used to forecast the pavement surface temperature after 3 hours and warn when it will drop below freezing. By using this neuro-model, it is possible to adopt an effective anti-icing practice for maintaining winter roads.

View full abstract

Center notched concrete beams reinforced with carbon fiber (CFRP) and glass fiber (GFRP) reinforced plastic sheets were subjected to three-point bending. Fracture process and reinforcing effect were quantitatively evaluated by the analysis of AE signals detected during the tests. A moment tensor analysis showed that the fracture progresses in three stages, where cracks were generated in a small region at the notch tip, then along with main crack extension, initiation and extension of an inclined crack (45-degree) occurred from the tensile zone to the notch tip, and finally cracks were generated near the interface between the fiber sheet and concrete. It was shown that the load of crack initiation and the maximum load in the first stage of the fracture process increase greatly by the reinforcing effect of the bonded fiber sheets.

View full abstract

The analytical study on the development of the homogenization of permeability in concrete, which is composed of crack and uncracked region, was performed. The applicability of the proposed model was estimated due to the comparison with the leakage water experiments. Further, the homogenized permeability in concrete having the complex crack pattern was also estimated analytically. In the proposed model, concrete is composed of crack and uncracked region and then the discontinuity of hydraulic gradient on cracks are taken into account in micro-level.

View full abstract

This paper is intended to report the results of the two-dimensional elastic analysis for test specimens consisting of two layers: an asphalt mixture to which the beam theory is inapplicable due to its low stiffness, and a thin steel plate on which the mixture is placed. Then, numerical computation has provided the authors with valuable data and information, such as the sizes and shapes of test specimens, friction between the upper and the lower layers, and the stiffness ratio between the two layers. All of these are essential factors in determining the mechanical property of a mixture by using the results of displacement measurement for the purpose of evaluating the elasticity of a pavement mixture.

View full abstract

The process for developing a structural design method for airport asphalt pavements with lean concrete base from experimental tests was described. First, the structural and functional capabilities of the pavement structure were investigated. It was revealed that joint is the critical loading position, and that both a thicker asphalt surface course and a crusher-run subbase are beneficial. Then, the structural parameters were studied through back-calculation and calibration. By using the elastic-layered system theory, the design principle was developed considering the influence of the joint and the fatigue property of the lean concrete base. Finally, applications of the design principle were investigated.

View full abstract