Under the seismic load action, the horizontal force will be significant, and the column in the moment resisting frame (MRF) shall resist the axial force and the shear force (i.e. This load condition is so called beam-column). In the Ultimate Limit State (ULS) design, the inelastic characteristics are used; strong-column weak-beam philosophy is used to prevent the collapse of the structure. The column overstrength factor (COF) is checked between the capacity of the connected beams and columns; the full plastic moment considering the axial force is used. Therefore, it is crucial to guaranty that the columns can resist the full plastic moment. The structural performance of the beam-column will be affected by the axial force level, and second-order effects might be dominant in a relatively slender column. In this paper, the second-order effect introduced by compressive axial force to the beam-column is studied by numerical simulation.
Roughness-induced stress shielding effect under cyclic Mode II loading caused by fracture surface roughness, i.e., the effect of decreasing loading stress intensity factor K, is investigated. A fatigue crack propagation test by applying cyclic Mode II loading on a small textured material is performed. The decrease in K is a few percent quantitatively, and the decrease is sufficiently small to ignore. Using the failure surface observation results, we discuss the mechanism of the fatigue crack propagation during cyclic Mode II loading on the textured material and validate the repeated crack propagation mechanism of damage accumulation, void formation, and coalescence.
Methane is one of the greenhouse gases emitted from paddy soil ecosystems and may induce global warming and climate change; therefore, mitigation options are urgently required to establish mitigation technology to reduce methane emission without affecting rice production. Methane is produced by a balance between oxidizing agents (such as iron) and reducing agents (easily decomposable soil organic matter), according to the so-called Takai theory. To evaluate options for mitigating methane production potential and to examine the applicability of the Takai theory in Southeast Asian paddy soils, 23 soil samples were collected from Thailand, Indonesia, Philippines, and Vietnam. These soil samples were anaerobically incubated to measure their methane production potential and examined to see whether their chemical properties, such as the ferrous, total iron, and organic matter contents, were correlated. We found a significant negative correlation between the methane production potential and the total iron content, and a positive correlation between the methane production potential and the hexose content, as an index for a soil's easily decomposable organic matter content. The methane-C/CO2-C production ratio was also positively correlated with the mineralizable nitrogen/ferrous contents ratio, which indicated that the Takai theory, established for Japanese paddy soils, is also useful in Southeast Asian paddy soils and that the soil's iron content is important to estimate the methane production potential.
The phase transformation behavior from austenite upon cooling in a 1.5Mn-1.5Si-0.2C steel was in situ monitored using dilatometry, X-ray and neutron diffractions. The starting temperature of ferrite transformation was in good agreement between dilatometry and neutron diffraction, whereas much higher in X-ray diffraction. Such a discrepancy in transformation temperature is attributed to the change in chemical composition near the surface of a specimen heated to elevated temperatures in a helium gas atmosphere for X-ray diffraction. In situ neutron diffraction enables us to investigate the changes in lattice constants of ferrite and austenite, which are affected by not only thermal contraction but also transformation strains, thermal misfit strains and carbon enrichment in austenite. Pearlite transformation started after carbon enrichment in austenite reached approximately 0.7 mass% and contributed to diffraction line broadening.
In the field of ironmaking, there are few in situ non-destructive techniques for systematically evaluating the reduction behaviors of blast furnace (BF) burden materials. The standard method for the evaluation of the reduction disintegration index (RDI) includes low temperature reduction with a constant gas composition at a constant temperature followed by a cold strength test after cooling. During the reduction of iron ore burden in the BF, reduction disintegration proceeds in the course of increasing temperature through crack generation and propagation caused by volume expansion due to the reduction from hematite to magnetite. Acoustic emission (AE) method is an in situ non-destructive technique to evaluate the crack generation and propagation phenomena in various fields. In this study, we first attempted to apply AE method for a detailed in situ observation of BF burden materials by a combinational experiment of reduction disintegration. In the case of single-particle reduction, it was possible to detect AEs without friction between the sample and the waveguide giving rise to noise. Although a large number of AEs were measured during cooling of both sinter and pellet, the AE energy of the sinter was larger than that of the pellet. Furthermore, a significant number of AEs were also detected during heating of lump ore containing larger amount of combined water indicating possibility to evaluate the decrepitation behavior of such ores. By the packed bed reduction tests, which could evaluate average properties of iron ore burden, it was found that the AE energy attributed to thermal stress observed during cooling was higher than that to reduction degradation. These results suggest that it will be possible to eliminate the influence of crack generation within the iron ore burdens in the cooling stage by applying the in-situ non-destructive evaluation method developed in this study. It is also expected to apply for the quantitative estimation of the reduction disintegration behavior of burdens in the working BF.
