The mechanical anchorages of main bars in beam-column joints of reinforced concrete structures are tried to use in some construction systems. In these systems, the nuts with small flange which can be arranged at minimum required spacing are used as mechanical anchorages, but the design concept of the mechanical anchorage in reinforced concrete structures is not established yet. Ninety eight pull-out tests have already been carried out to clarify the development mechanism of the mechanical anchorage and to evaluate the ultimate anchorage capacities. The equation to predict the ultimate capacity of the mechanical anchorage is proposed in this paper. The predicted capacities agree with the experimental ones which were obtained in this experimental study or in previous experimental studies by other facilities.
In order to investigate a method for joining concrete and the permanent form made of fiber reinforced cement, the shearing stress transfer properties between concrete and GRC (glass fiber reinforced cement) panel which has deformed surface, was examined by single shear test and numerical analysis. The adequate shear strength which was a load divided by length of specimen, was proposed as a parameter to measure the shearing strength on the joining interface between concrete and GRC panel. As a result, the width of the rib on joining interface had an influence upon the shearing stress transfer properties. It was made clear that putting a rib which has better width to joining interface of GRC panel was an effective method to improve the joining performance between GRC panel and concrete. In this study the appropriate width of the rib on GRC panel was from 0.7 cm to 1.0 cm (when deformed surface of GRC panel was a depression) and above 0.5 cm (when deformed surface of GRC panel was a.convexity).
In this paper, new method of damage evaluation of reinforced concrete beam of which ultimate limit state is reached by shear failure after yielding under reversed cyclic loading such as earth-quake motion is proposed. The proposed method is based on dissipated energy of perfectly elasto-plastic body. In the proposed method, revision factor is adopted in order to consider the influence of cyclic loading at the same displacement on damage. The damage of reinforced concrete beams of which ultimate limit state is reached by shear failure after yielding is quantitatively evaluated and the proposed method is shown to be reasonable.
To reuse concrete returned from job sites, the method to remain the fresh properties of the returned concrete for a long time was studied by stopping cement hydration temporarily and adding an activator to the concrete next day to reuse in the same manner as an ordinary concrete. At the same time of adding an stabilizer, a superplasticizer was added to obtain the consistency with slump of 22cm or so. As a result, the slump of approximately 18cm was obtained next day. The reactivated concrete exhibits equal bleeding, compressive strength, freeze resistance, and change in length to ordinary concrete. The setting time of returned concrete reactivated retards as stabilized concrete retards. However, the setting time of the reactivated concrete mixed with returned concrete and new concrete becomes equal to that of ordinary concrete.
Reinforced concrete earthquake-resistant frames are generally designed on the basis of “strong-column weak-beam”concept. Besides, shear failure of beam-column joints should be avoided in order that the frames exhibit adequate ductile performance. Joint shear failure occurs when the shear stress level is enough large, but the shear failure mechanism is different between the conditions with and without adjacent beam yielding. The experimental study shows that the joint shear failure results from the compressive fracture of joint concrete in which the compressive strength deterioration occurs due to shear cracking. And joint reinforcement makes a large influence on the joint shear strength when adjacent beams yield, because the joint reinforcement becomes the principal confinement for the joint concrete.
To obtain a super workable concrete which can be cast without vibration, both deformability and resistance to segregation must be taken into consideration. Some agents made from polysaccha-rides are reported to have resistible activities of material segregation, but there is no report on an application of polyamino acids as a resistible agent to segregation. Then, we applied to use a γ-polyglutamic acid (γ-PGA) for the agent. As the result, the super workable concrete containing the γ-PGA produced from Bacillus subtilis (natto) indicated a suitable resistance to segregation. To estimate the mechanism of the resistible activity, the plastic viscosity and the yield value of cement pastes were measured. The γ-PGA increased the yield value rather than the plastic viscosity. It was suggested that the γ-PGA contributed to making the interaction between cement particles without increasing the viscosity of water.
The quality of shotcrete is lower than that of cast-in-place concrete because of its materials used and its construction process. Objectives of this study are to improve several properties of shotcrete and to enable us to manufacture high-quality shotcrete. The results obtained within the scope of this study may be summarized as follows :High-quality shotcrete can be economically manufactured by using a water reducing agent, not increasing unit water content, because a dosage of a set accelerating agent can be decreased. Compressive strength and the resistance to carbonation of shotcrete can be improved by using a set accelerating agent whose principal ingredient is calcium sulfoaluminate. The resistance to freezing and thawing of shotcrete can also be improved by incorporating plastic hollow microspheres that act as an air entraining agent, however the shotcrete does not necessarily possess sufficient durability due to the existence of large pores like honeycomb induced by shotcreting.
A study on the strength development under freezing condition and the freezing behavior of water in concrete with and without accerelatores for freeze protection was carried out. The concrete contained accerelatores for freeze protection cured at 20°C have shown strength gain in both short and long term superiority over AE ordinary concrete. At the same maturity, the strength of the specimens which contained accerelatores for freeze protection higher than standard dosage cured under freezing conditions was even higher than that of AE ordinary concrete specimens cured at 20°C. Strength development under freezing condition was influenced by the amount of unfrozen water in concrete. Freezing behavior and self-drying were measured by means of a method to estimate moisture contents as a function of resistivity and temperature. Unfrozen water in concrete was increased by using accerelatores for freeze protection. The strength of concrete using accerelatores for freeze protection to prevent the frost damage at early ages would be lower than that of AE ordinary concrete.
In evaluating the concrete finishings, people depend not only on visual sense but also on the tactile one. This paper focuses on the relation of visual-tactile response with visual one and with tactile one. As a conclusion, the perception of finishing variously changes with the distance between people and the material. People feel the material richer, which looks different with the change of distance. Within a close distance, the finishing that looks soft wins a good evaluation, but the evaluation drastically changes with the touch of the material. Visual-tactile comfort for concrete finishing needs surface with tactile smoothness and visual richness. It is reason the tactile response plays a crucial role on the perception of visual-tactile sense.The tactile response of concrete simply shows a linear relationship with the smooth degree of the surface. Therefore, the finishing is divided into two kinds. The finishing with smooth surface makes people comfort, and this is important on the difference of temperature.
This paper deals with an experimental study on the strength of the precast wall panels, which are connected with the upper and lower beams using prestressing, not connected with the columns of the both sides. The experimental parameters are as follows ; magnitude of prestressing, sizes of openings in the center of the wall panel for fastening prestressed concrete (PC) steel bars, joining PC steel bars or not, filling the openings up with PC grout or not, etc. The maximum strength of the wall panel is investigated from some phases as follows; the shear resisting mechanism by cumulating truss mechanism and compressive strut of concrete, moment capacity of the parts sandwiched in the openings, and the slip strength of the horizontal joint published by the authors.
The history of Japanese port and harbor construction by the use of concrete materials has more than five decades, and such a lot of concrete structures have been constructed and are in service. In order to keep these concrete structures in good service condition, a rational maintenance system is necessary. As a part of maintenance procedures, nondestructive testing of existing structures play very important roles. Considering such social and technical background, an experimental study on the application of AE (Acoustic Emission) technique as a nondestructive testing to deteriorated port and harbor concrete structures are carried out. From this experimental work, the following conclusions are derived. 1) Acoustic emission behaviors of concrete under uniaxial compression are strongly related to the pore structure of the concrete. 2) Acoustic emission behaviors of reinforced concrete beams under bending are related to the crack condition of concrete, even under low level bending moment.