2方向の曲げを受ける RC 長方形断面長柱が,ねじりを伴って破壊したことが報告されている.著者らは,このねじり現象は RC 断面のせん断中心の移動に起因するものと考えた.本研究では,シェル要素解析により,図心軸に2方向水平荷重を受ける RC 中空断面柱にねじりが生じることを確認するとともに,RC3 次元ファイバーモデルに薄肉構造部材の曲げ理論を適用することによりせん断中心の移動量およびせん断中心の移動により発生する付加ねじりモーメントを算定する手法の提案を行った.提案手法を用いてパラメトリック解析を行った結果,2方向入力を受けるRC断面はひび割れ,鉄筋降伏等により非対称な断面抵抗機構を形成するためせん断中心が移動し付加ねじりモーメントが発生することがわかった.
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The purpose of this study was to investigate the mechanism of shear strength degradation of a reinforced concrete (RC) member under cyclic loading. First, the shear failure after flexural yield of tension reinforcing bars of a RC column designed as bridge pier under cyclic loading was simulated by the method of three-dimensional rigid-body-spring-model (3D RBSM) and the shear strength degradation was quantitatively evaluated by a numerical approach. Afterward, based on the shear resistant mechanism, the degraded shear strengths after each load cycle were decoupled into the contributions provided by beam action and arch action, with the use of the numerical local stress results. As the important finding, the mechanism of shear strength degradation due to cyclic loading of the RC column was concluded as with the increase of deformation level, the arch action first degraded gradually whereas the beam action maintained its original capacity; then after losing most capacity of the arch action, the beam action began to decrease rapidly, which caused the shear failure.
Using Titania type electrodes that are liable to develop fisheyes in the deposit metal, depending upon the test method adopted, two kinds of specimens were prepared : one as weld and the other subjected to a hydrogen-removing treatment (250°C, 8h). They were put to a fatigue test on the Ono's Repeated Bending Fatigue Testing Machine, with the following results :1) In the former specimen, fatigue cracks originate from micro-blowholes lying somewhat deep under the surface; while in the latter, they do so from micro-blowholes very close to the surface. These micro-blowholes correspond to the nuclei of fisheyes appearing in tension test pieces.2) In the former, nominal stress, namely, fatigue limit with no consideration made for the locations of these micro-blowholes, is about 2-3kg/mm2 lower than in the latter (Fig.3). When, however, the crack-developing stress is considered, the difference well be about 10kg/mm2 (Fig. 5) ; this is presumably due to the variance of hydrogen content between the two.
Sudden loss of cryogenic helium coolant accident (ISS-LOCA) in the cryogenic distillation columns for the hydrogen isotope separation system (ISS) is one of the worst situations because it leads the evaporation of liquid hydrogen in the column. From this background, an intended ISS-LOCA test was conducted with an actual ITER-scale cryogenic distillation column. Sudden increase of internal pressure was not observed and enough time is found to recover the hydrogen isotope into a storage system if vacuum insulation is maintained and reboiler heaters are turned off immediately. In off-normal conditions, the rapid recovery of hydrogen in the column by an empty hydrogen storage bed is a reasonable hydrogen recovery scenario. Validity of the hydrogen recovery scenario was proved by a demonstration test.
The finite displacement theory considering the effect of shear deformation is formulated. In this research, the computer program using the stiffness equation of reinforced concrete structures has been developed for the ultimate deformation analysis under cyclic loadings. Cyclic loading tests of reinforced concrete columns under axial force was carried out and the applicability of this theory was investigated. The experimental values obtained from specimens in which axial force, web reinforcement ratio and a/d were changed are compared with the calculated values. It is possible to predict the flexure or shear failure theoretically, when the instability of structures is considered.
In this paper, numerical simulations of reinforced mortar beams subjected to projectile impact are conducted by using the proposed 3-D Rigid-Body-Spring Model (RBSM) in order to investigate mechanisms of crack propagation and scabbing mode of concrete members under high-velocity impact. The RBSM is one of the discrete-type numerical methods, which represents a continuum material as an assemblage of rigid particle interconnected by springs. The RBSM have advantages in modeling localized and oriented phenomena, such as cracking, its propagation, frictional slip and so on, in concrete structures. The authors have already developed constitutive models for the 3D RBSM with random geometry generated Voronoi diagram in order to quantitatively evaluate the mechanical responses of concrete including softening and localization fractures, and have shown that the model can simulate cracking and various failure modes of reinforced concrete structures. In the target tests, projectile velocity is set 200m/s. The reinforced mortar beams with or without the shear reinforcing steel plates were used to investigate the effects of shear reinforcement on the crack propagation and the local failure modes. By comparing the numerical results with the test results, it is confirmed that the proposed model can reproduce well the crack propagation and the local failure behaviors. In addition, effects of the reinforcing plates on the stress wave and the crack propagation behaviors are discussed from the observation of the numerical simulation results. As a result, it was found that scabbing of reinforced mortar beams subjected to high velocity impact which is in the range of the tests is caused by mainly shear deformation of a beam.
