Abstract— Mode III fatigue crack propagation tests were conducted on circumferentially cracked bars of a medium carbon steel under a constant value of the J ‐integral range. The Δ J value was evaluated from the loading part of the hysteresis loop of the applied torque and the angle of twist. The fracture surface was macroscopically flat for all cases examined in the present study. The crack propagation rate decreased with crack extension, because of the shear contact of the crack faces. The crack propagation rate, without contact shielding, obtained by extrapolating the relation between the crack propagation rate and the crack length to the pre‐crack length, was a power function of Δ J irrespective of the initial notch depth.
Rebar corrosion and corrosion-induced crack are one of the major deteriorations of concrete structures. The corrosion-induced crack accelerates the corrosion and deterioration processes and can involve concrete cover delamination. It is necessary to assess rebar corrosion and internal damage to avoid cover delamination and to judge the damage level during maintenance procedures. The authors have been developing a non-destructive test method to detect both of rebar corrosion and internal crack area by using electromagnetic wave radar. The feature of developed assessment method is that the Self-Organizing Map (SOM) is applied to evaluate the change of reflection waveform data obtained by electromagnetic wave radar due to rebar corrosion and internal crack. The specimens with a cover thickness of 30 and 60 mm with corrosion-induced internal crack were made for the electrolytic corrosion experiment and the developed assessment method was applied. As a result, in the case of the specimen before corrosion, it was distinctly classified as rebar and concrete. The result for the specimens after corrosion showed that the rebar corrosion area was different from the sound case. Moreover, the area well coincided with the internal crack area. The developed method succeeded to detect quantitatively not only rebar corrosion position but also the internal crack area of more than 0.1mm crack width for the condition of cover thickness less than 60 mm and corrosion ratio larger than about 4%.
A newly developed coupled numerical model is presented to investigate the compressive localization and softening behavior of concrete under steel tube confinement. The coupled model combines the use of rigid body spring model (RBSM) and nonlinear shell finite element method (FEM) to simulate concrete and steel in steel tube–confined concrete members. Numerical evaluation of compression localization in steel tube–confined concrete columns showed that the compressive behavior of this type of column is also localized and that the length of compressive fracture zone was found to be more localized in square cross section than equivalent circular cross section. With increasing slenderness and level of confinement, it was found that localization length increases with increasing confinement, and for higher confinement level, localization zone can only be observed in longer specimens. This means that localization and softening of concrete can always occur irrespective of confinement level but depends on the size (height) of the member.
主筋およびせん断補強筋に連続繊維補強材を用いたコンクリートはりの実験および解析を行うことで, 連続繊維で補強したコンクリートはりのせん断耐荷力の評価を試みた. 主筋に連続繊維補強材を用いた場合には, 斜め引張破壊強度に及ぼす主筋弾性係数の影響を解析的に明らかにし, その強度評価方法を示した. 一方, せん断補強筋に連続繊維補強材を用いた場合には, 曲げ成形部の強度に注目し, その強度算定式を理論的に導くとともに, 最終的にせん断補強筋の破断で破壊に至るはりのせん断耐荷力評価方法を検討した.
