Hisato Hotta

Leakage of gas through concrete cracks

Abstract This paper aims at formulating the gas leakage rate through cracks in concrete walls. Leakage tests were carried out using eighteen specimens. Five specimens with a reinforcing bar and thirteen without were tested. The kind of fine aggregate and the size of the coarse aggregate were varied. Crushed gravel was used as the coarse aggregate. In order to examine the dispersion of the experimental results, four or five specimens with the same dimensions and of the same type of concrete were tested. The experimental results were formulated accurately by an isothermal compressible-flow equation for each identified crack. The two-dimensional Poiseuille-flow equation was also applied successfully for a small leakage rate. The dispersion of the test data from the same specimens, the influence of the aggregate and the effect of the reinforcing bar are discussed. It is concluded that the influence of the aggregate can be neglected and that the reinforcing bar reduces the leakage rate. Finally, the gas leakage rate through a concrete crack is presented.

Influence of drying and water supplying after drying on tensile strength of cement mortar

Abstract This paper is concerned with the change in tensile strength of cement mortar sibjected to rapid drying and water supply after drying. Flexural strength was investigated for several cement paste specimens cured in water for a certain period, with some specimens dried for 1 day and cured again in water after drying. As a result, it is known that the flexural strength of the specimen allowed to dry becomes about 1 3 of that of a sound specimen, but it is almost recovered after about 3 h water curing after drying. The reason why the strength changes is usually connected with a restrained stress due to drying shrinkage and a stress relaxation due to expansion caused by water absorption. However, when the restrained stress at the surface overtakes the tensile strength, and a considerable number of minute cracks occur, as was observed, the above explanation cannot be accepted, because the tensile stress is almost perfectly relaxed by the occurrence of the cracks. In this paper, the reason for the strength recovery as a result of water absorption is reconsidered by means of stress analysis and microscopic examination of the cracks.

Compressive Strength of Concrete in Flexural Critical Region of Reinforced Concrete Beam-Column Members

The compressive strength of concrete in flexural critical regions of reinforced concrete beam-column members is investigated experimentally and in terms of three-dimensional finite element predictions. Reinforced concrete beam-column members subjected to an axial load combined with single or double curvature bending were manufactured with special stirrups that minimize the confining effect of concrete by stirrups. Due to the existence of a beam-column joint near the flexural critical section at both ends of the members, the concrete on the compression fibers around the joint is subject to multiaxial compressive stress states; and the compressive stress in the region exceeds the uniaxial compressive strength of concrete. In the case of double curvature bending, the load-carrying capacities of the beam-column members which are measured experimentally and predicted by means of finite element analysis greatly exceed the moment and axial force interaction curve obtained from the uniaxial stress-strain curve of concrete.

Empirical investigation on buckling and post-buckling behaviour of cell liners

In nuclear-related facilities, many concete walls and slabs are lined with thin stainless steel plates in order to insure against the risk of accidental air leakage during a severe earthquake. These liners are forcibly deformed with the deformation of the concrete walls and slabs during an earthquake. The purpose of this paper is to obtain basic empirical data on the shearing behaviour of thin steel plates attached to concrete, especially to understand the relationship between the shear strain of the plate and its lateral displacement, as fundamental research on the safety of lining plates. A new apparatus for measuring the lateral displacement of a lining plate by continuously scanning its surface is tested. The apparatus proves to be quite effective for understanding the buckling wave of the lining plate and the essential behaviour of a thin steel plate attached to a concrete wall subject to a shear force is clarified.