The lack of the durability in concrete structures is reported widely as serious problems. To keep the safety of structures and to confirm the long service life, the development of effective non-destructive evaluation method for defects is in urgent demand. In this paper, an evaluation method for cracks and internal planar defects in concrete members is studied by using the ultrasonic spectroscopy. Spectral responses obtained by using sweep mode input of a function generator are applied to evaluate these cracks and defects. In experiments, artificial surface cracks normal to the axis and planar defects embedded parallel to the surface in concrete members are investigated quantitatively. Two-dimensional resonance analysis of the members with these defects is performed by using the Boundary Element Method (BEM). These results show that the present method is promising as quantitative evaluation method of the cracks and defects in concrete members.
This paper discussed the mechanical properties of hybrid structures, which composed of a reinforced concrete beam and steel columns. Analytical methods and loading tests were carried out. A Concentrated load was applied to four-types of specimens. Under the state of serviceability limit, it was made clear that moment distribution of hybrid portal frame could be calculated in consideration of decease of flexural rigidity. After the steel yielding of the reinforced concrete beam, moment redistribution were ocurred and portal frame was finally collapsed in flexure. It was found adequate to apply the design method of flexural rigidities and moment redistribution proposed in JSCE code.
The shear transfer mechanism of shear walls can be explained by truss analogy. This means that conventional reinforcing method is not so effective. The authors, therefore, proposed a new method of shear reinforcemen and conducted a test to investigate the validity of the proposed method. The test resulted in the following finding : Brittle failure of shear walls is, generally, caused by shear failure of columns reacting to compression struts. But thi failure can be prevented by using the new reinforcing method. Arch action can be controlled by arranging concentrate, bars in a specific position. High strength round bars act as effective reinforcements. The ultimate strength can be estimated by using flexure theory and truss analogy.
The object of this study is to clarify experimentally and analytically the pullout behavior of axial bars from a footing. The experiments for RC columns subjected to alternate cyclic loadings and the pullout tests for anchorage zone were carried out, and the influences of several factors on slippage of bars have been quantitatively investigated. Furthermore, bondslip model obtained from the results by the finite element method as well as the pullout tests in massive concrete was used in order to evaluate the slippage of bars from the footing. Also, the process of bond mechanism was taken into consideration in order to express the deterioration of bond stress along bars. Calculated values on the basis of proposed method for the evaluation of the slippage of bars have a good agreement with the experimental results.
The effects of axial load on a SRC beamcolumn subjected to a constant axial load and a bending moment have been studied by many researchers. However, the collapse mechanism of columns has not yet been investigated theoretically. In this paper, using a finite difference equation and an elasto-plastic numerical analysis, we investigate the basic behavior and the collapse mechanism of the columns having various axial load ratio. Based on the analytical results, we show that there exists a stability limit axial force in SRC beamcolumns forced a constant axial load and a repeated bending. As a result, it is verified that if the axial load is less than the stability limit axial force, then the column will keep its bending strength, and therefore, it will have a stable behavior.
The size effects and the shape effects (square or circular cross-section) on the flexural strength of concrete are investigated through experiments and numerical analysis with fracture mechanics concepts. Based on the numerical results, we proposed equations for estimating the flexural strength of concrete beams with square or circular cross-section. The beam depth, the tensile strength and the characteristic length of concrete are the variables in the proposed equations. The estimated values of the flexural strength through the equation are in good accordance with the experimental results especially for the square beams. The equation gives moderate values for the flexural strengths of various kinds of concrete including normal concrete, high strength concrete, lightweight concrete, mortar and polyester resin concrete.
This paper describes the test results on the electrical insulation properties of the epoxy-coated reinforc-ing bar. By a series of testing, the effects of mechanical stress cycles, electrical cycles, chemical corrosion and high temperature, were also evaluated. Even after the several degradation cycles simulating the severe environments in fusion reactor, the epoxy-coated reinforcing bar and its mechanical joint have excellent insulation properties in comparing to the conventional insulation structure, and they demonstrated the adequate applicability for the RC-structures of large electrical devices such as electrical power plant, fusion reactor, intelligent building and linear-motor transport system.
In response to rapid constructions for marine structures, the authors have conducted structural researches on composite prestressed concrete structures, which consist of precast concrete blocks and filled-in concrete and steel pipe piles. This method is secured by the bondage and bearing capabilities for the columns and beams joints, where columns of precast blocks and filled-in concrete are prestressed. Thus, this type of structure by its nature could not anchor the main reinforcing bars of beams into the columns. Therefore, the authors conducted the structural tests for the purpose of studying the behaviors of these special joints. The results of tests show that these joints could function as a joint of a rigid frame from ample transmittance of bending moments of beams into columns and no excessive displacements.
In order to clarify the shear resistant behavior of beam-column joints with high strength concrete, reversed cyclic loading tests were carried out for four exterior beam-column subassemblages. Amount and yield stress of joint hoops, and loading history were chosen as experimental variables. The following remarks were obtained from the test results : (1) Increase of concrete strength reduces the deterioration of the joint stiffness due to reversed cyclic loading. (2) Existence of the joint hoops is also effective to control the excessive slip of the beam bar from the joint. (3) Joint shear strength of JS type may be proportional to the concrete strength. (4) The slighter joint damage was, the greater stress shift of the column bar toward the tension side occurred.
In order to make clear the bond splitting behavior of reinforced concrete members with high strength concrete, eighteen simply supported beam tests were carried out. But comparing the tests results with the existing design equation, the following remarks were obtained : (1) Bond strength is inversely proportional to the bond length for the case of having no transverse reinforcements. (2) The use of transverse reinforcements, especially of supplement ties is more effective for the high strength concrete. (3) The greater concrete strength is, the smaller the bond strength difference between top bar and bottom bar is. Furthermore, the new experimental equation considering these remarks was proposed on the basis of Fujii-Morita's equation. The applicability of this proposal was verified by the latest Japanese invpstigator's toct reciiits.
Alkali-Silica reaction has been identified as one of main causes for premature deterioration of concrete structures, and many papers have been published dealing with various aspects of the mechanism and effects. However, a comprehension method to predict the extent of reaction and the ensuring damage has not yet been established. In this paper, an attempt has been made to present a new model based on kinetics to predict the extent of reaction between reactive aggregate and the surrounding cement matrix. The model also incorporates the affect of diverse factors such as size and reactivity of aggregate, alkalinity of cement matrix, etc. It was found that the results obtained from the simple chemical test (ASTM C 289) can be explained on the basis of the model proposed here.
Reversed cyclic bending tests were performed on reinforced concrete beams reinforced with large-sized deformed bars. These bars designated as D 64, having nominal diameter of 64 mm and screw-type rolled deformation, have been developed to apply large-scaled structures such as nuclear power plants and other containment structures. It was shown from the comparison between specimens reinforced with D64 and half-scale specimens reinforced with D32 that there is no scale effect in crack pattern and flexural deformation behavior in pre- and post-yielding stages. This means that the maximum surface crack width at a given steel stress increased proportionally with the increase of bar diameter because bar spacing and concrete cover were determined in proportion to bar diameter in these beams. It was demonstrated that the additional arrangement of welded deformed bar mat near the bottom concrete surface at 10 mm concrete cover decreased drastically the maximum surface crack width.