During the Northridge earthquake and the Kobe earthquake unexpected brittle fractures occurred in a number of steel structures. The brittle fracture during earthquakes initiates from a shallower initial crack than that of well-known brittle fractures. This study addresses the shallow crack tip stress field at brittle fracture transition. The crack tip stress field at the instant of brittle fracture is investigated based on the experiments and FE analyses which employed specimens with precrack on notch. As a result, it was confirmed that crack value of maximum principal stress, stress triaxiality and Weibull stress at shallow crack tip is affected by the notch shape and crack depth.
Connections between a bracket flange and a main girder are fabricated by full penetration welds. Generally, the joints at the lower flange of the bracket are subjected to cyclic compressive stresses. It means that there is a possibility to change the welding method between the lower flange of the bracket and the main girder into partial joint penetration in terms of fatigue strength under compression. In this study, the fatigue strength of the base joints of the brackets was examined. The test results revealed that the joints have enough fatigue strength under the compressive stress even though partial joint penetration is applied there.
Channel steel columns utilized for industrialized steel houses have a buckling mode including bending and twisting. Their strength of flexural torsional buckling is lower than their strength of flexural buckling. However, their strength of flexural torsional buckling can be improved by stiffening members relatively easily, because they buckle in elastic range and their plate thickness is thin. This paper describes improvement on their strength of flexural torsional buckling and detail of their buckling mode by means of energy method.
This paper is concerned with yield surface useful for the simplified dynamic model for 3-dimensional multi-story steel moment frames with eccentricity. The authors propose a couple of new expression of yield surface on simplified dynamic model for each story that consists of beams and columns. The yield surfaces of each story were examined through simple plastic analysis for the frame, which has multiple structural planes. To calibrate the validity of the yield surface, two kinds of frames, which consist of beam yielding mechanism and column yielding mechanism, were used. Adopting new expression of yield surface, a higher accuracy of results can be acquired.
This research proposed an additional strengthening of the brace made of angles, and vibration control performance was verified in cyclic loading test. A joint of angle-buckling restrained brace（angle-BRB） has a cross-sectional component with combining the two angles inserted a gusset. Then, the geometric symmetry section of angle-BRB prevented an eccentricity bender effect. After obtaining these static experimental results, the energy absorption capacity as a vibration control member was performed in the hybrid response test.
In “Recommendation for the design and fabrication of tubular truss structures in steel (Japan)” , asymmetrical KK joint is outside the scope. However, asymmetrical KK joint may be needed for architectural design. So, in this study, the influence of asymmetry of a joint to the strength is examined by using FE analysis. First, simulation analysis of past experimental result is conducted for validity of analysis method. Then, using this analysis method, the influence of asymmetry of a joint is examined, through comparison with symmetrical joints. Moreover, an evaluation method for asymmetrical KK joint is proposed.
Recently, many kinds of weathering steel were widely used in steel bridges. Ni-advanced weathering steel are new types of weathering steel. It was considered that the quality of these steels has been remarkably improved. However, when it had come to how much, it had not been clarified. Therefore, in the past, we had investigated Nickel-advanced weathering steel on the basis of the mill sheet in order to clarify their quality, and these steel mechanical properties had been shown . In this paper, we investigated the chemical compositions of these steels. Investigated component were Carbon, Silicon, Manganese, Phosphors, Sulfur, Copper, Chrome, Nickel including PCM(Cracking Parameter of Material), Ceq(Carbon equivalent) and V-value (Weathering Alloy Index), and these results were shown. We also showed the improvement factor in the quality, comparing with the conventional weathering steel data.