Fourteen subassemblage frame tests have already been carried out to investigate the load carrying capacity and ductility of beam-column joints with mechanical anchorages. The proposed equations on mechanical anchorage capacities are also verified in these tests. The load carrying capacity and ductility of beam-column joints with mechanical anchorages under three failure types (flexural yielding of a beam, shear failure of a joint, and side splitting failure of concrete cover around anchorage) are discussed by comparing with those with 90-deg. hooked bar anchorages based on frame test results. The physical performance of mechanical anchorages is approximately equal to that of 90-deg. hooked bar anchorages.
From a point of view that the rates of development of ultrasonic pulse velocity, dynamic modulus of elasticity, and rebound hardness are more rapid than the one of strength at early ages, experiments were carried out to obtain the optimum ages for nondestructive testing respectively. It is concluded that the optimum age for ultrasonic method for evaluating potential quality of concrete is 1-day and the one for rebound hardness method is 3-day practically and the earlier the better. It is also concluded that the combined method is effective at early age. Based on the results, a method combined 1-day pulse velocity with 3-day rebound number is ecommended for earlier inspection of concrete quality in structures.
Authors have devised a method of improving seismic performance of concrete filled square steel tubular columns. In this method circular steel tubes are embedded in infilled concrete to confine the inner concrete. In order to verify the efficiency of this method, experimental investigations were conducted. Alternately reversed cyclic shear-bending tests under constant axial load had been carried out for the columns reinforced by embedded circular steel tubes and non-reinforced columns. In this paper the test results are described and discussed.
Effective factors on shear resistance of R/C interior beam-column joints were analyzed by using experimental data including 243 specimens tested in Japan and abroad. A reliable equation to evaluate the joint shear strength was proposed using the regression analysis of the shear strength and three factors : concrete strength, column axial stress and bond index which was consisted of joint reinforcement and beam bar bond stress in the joint. The failure modes in joint shear and in beam/column flexure can be easily distinguished by this equation. On the other hand, the joint shear strength calculated from concrete effective compression strength of diagonal joint strut idealized by the authors and from joint reinforcements, showed good approximation to the experimental values. These results support that shear stress transfer of interior beam-column joints consists of the strut and truss mechanisms.
The purpose of this study is to propose the shear resisting mechanism and the evaluation formulas of shear strength for top slab of caisson foundation, which is RC deep slab simply supported at the all edges. Namely, the resisting model and the formulas for shear strength of top slab was studied from the internal stress and reaction force distribution of top slab varying configuration and shear span ratio and so on by means of FEM, under vertical force with or without eccentricity. Compared with the experimental results, the proposed formulas were demonstrated that they possessed high accuracy and simplicity. Finally, the application of this study to the limit state design of top slab was also referred.
This paper evaluates the surface finishing of concrete buildings due to the effect of ageing. The surface finishing is evaluated on the micro level of material and macro level of the building. It was found that on the level of material, concrete becoming dirty makes the beauty decrease. However the beauty can also increase due to uniform dirtiness. On the level of building, the gorgeous-modest factor represents the activity, has high correlation with the degree of dirtiness, and changes from “gorgeous” to “modest” with ageing. The rich-poor factor represents the total evaluations of facade, depends on the distribution of dirt and on shape of facade rather than on dirty degree.
The purpose of this paper is to investigate the pumpability of SWC (Super Workable Concrete). SWC which has the property of self-compacting is being widely used for various structure but often causes the decline of slumpflow by pumping. SWC which mixed ordinary portland cement and flyash was mainly used in this experiment. It was found that the decline of slumpflow was related to the properties of concrete and the conditions of pumping. The properties of concrete were the mix proportions such as the ratio of cement and flyash, kinds of admixture and the size of slumpflow before pumping. The conditions of pumping were the velocity of concrete in pipeline, the total length and the shape of pipe. Above all, the decline of slumpflow tends to be related to the degree of pressure loss. In addition to slumpflow, the changes of the fluidity of wet-screening mortar, pressured bleeding ratio, strength, durability factor and pore volume were confirmed by pumping experiment.
This paper discribes the influence of properties of recycled fine aggregate on carbonation and frost resistance of recycled fine aggregate concrete. According to the results of experiments, the rate of carbonation is fast with the percentage of water absorption of the recycled fine aggregate increase. When the water absorption of recycled fine aggregate is under about 7%, the frost resistance can be improved by using the coarse aggregate of good quality, and by entraining the appropriate air volume.
The materials exhibit continuous or discontinuous deformation modes when quasi-brittle solids like concrete and rock are deformed into plastic region. In particular, we have been concerned mainly with localized failure characteristic (Co-continuity) of hardening-softening elasto-plastic materials. In this paper, first, we distinguish diffuse failure from localized failure according to the degree of continuity or rather discontinuity of the underlying kinematic fields. In addition, singularities with regard to both failure modes are examined by minimization of second order work density and eigenvalue analysis. By introducing Drucker-Prager material with Wu-Tanabe's model, numerical simulations are carried out. Then, we obtained the characteristics of the brittle-ductile transition and diagnosis of failure modes in proportional and non-proportional loading. Finally, analyses of post-localized failure are attained so as to examine the mechanical characteristic around discontinuous surface under the Co-continuity.
This paper deals with an experimental study on the maximum strength of the frame in which precast concrete wall panel is inserted, which is connected with the upper and lower beams using prestressing, and is not connected with the columns of the both sides. We have investigated the specimens classified by three typical failure modes, which are slip failure at horizontal joint of wall panel, flexural failure at the parts sandwiched by openings located in the center of wall panel and shear failure of wall panel. Basically we have certified that the maximum strength of the frame in which precast concrete wall panel is inserted is almost the same as the sum of the minimum values of the strength correponding to the above three failure modes and the strength of the frame in itself
In order to reduce the labor needed in the construction of high with large section, a new construction method, which could reduce the section area of pier and the number of reinforcing bar, was developed. In the construction method, D 51 high strength reinforcing bar with yielding strength of 685 N/mm2 is used for longitudinal reinforcement, and high strength concrete with design strength of larger than 50 N/mm2 is adopted. In case of using high strength reinforcing bar forlongitudinal reinforcement, cut of reinforcing bar may occur before the crushing of concrete, if reinforcement ratio and material properties are not suitably adopted. In this study, the effects of material properties, such as yield ratio of reinforcing bar, the length of yield shelf and ultimate strain, and reinforcement ratio on the behavior of high pier were investigated through experiment and analysis. It was found that cut of reinforcing bar could be judged through section analysis. Throughthis study, the required properties of high strength reinforcing bar when being used for longitudinalreinforcement of high pier were clarified
Corrosion of reinforcement in concrete structures is one of the serious deterioration. Because the crack or the reduction of cross section of reinforcement by corrosion causes the deterioration of theperformance of structures or the functional disorder of structures. In this study, we discuss the method for evaluating the state of corrosion in the actual structures based on the condition of current structures and environmental condition. Then we assume that the carbonation depth is not only the index of pH value at bar location but also the index of oxygen supply at bar location. The model for evaluating the state of corrosion is constructed as the neural network trained by the data from site investigation. The effect of the factors on the progress of corrosion is discussed by the network, The network indicated quantitatively that the condition for occurrence of corrosion and the condition for the corrosion to be severely. In addition, it is clarify that the progress of corrosion is possible to be predicted by the combination of the neural network, prediction method for the carbonation and chloride movement referred from past studies.
In recent years, high-performance concrete and high strength concrete have been developed actively. Minenal admixtures such as blast furnance slag, fly ash and lime powder are indispensable for high-performance concrete and high strength concrete. However, the influence of mineral admixture on the process of chloride ion penetration into hardened concrete is not still fully understood. Therefore, it is necessary to clarify that the influence of admixtures on the process of chloride ion penetration into hardened concrete in case of reinforced concrete structures on the seashore. So, the authors experimented on the influence of mineral admixture on the process of chloride ion penetration into hardened concrete.