As aging steel structures increase, it becomes more important to evaluate the residual strengths of the structures in a quantitative manner. In this paper, axial compressive strength of corroded channel and angle steel members obtained from truss structures that were used for about 40 years was extensively studied with experiments and numerical analyses. They showed that the members had quite complex behavior such as local buckling, global flexural buckling, yielding and their combined failure modes. It was also shown that the local failure became more critical for the members where the maximum sectional area loss was more than 40% to the original section, whereas where the loss was less than 40%, the strength seemed to be controlled by global buckling and yielding. Reasonably accurate strength formulae that can be used directly for design were proposed based primarily on conventional global flexural buckling strength formula with some modification factors. The accuracy and applicability of the formulae were also verified through FEM analyses.
This paper presents the damage mechanism of gymnasium building with RC frame and steel roof structure damaged by the 2011 Off the Pacific Coast of Tohoku Earthquake. The result of pushover analysis reveals that the damage at top of column progresses from the frame with seismic walls to the moment resisting frame. Furthermore, the damages at top of column around the frame with seismic walls are confirmed by seismic response analysis. Additionally, the cause of the difference between push over analysis and seismic response analysis is investigated in terms of the distribution of external forces and shear forces at the top of column.
A lot of fatigue cracks have been observed in welded joints between deck plates and vertical stiffeners of orthotropic steel decks under severe traffic load. Stop-hole method for preventing the extension of fatigue cracks is often used as a countermeasure against these fatigue cracks. However, its effect has not been so clear yet. In this study, for the purpose of making clear the effect of the stop-hole method, fatigue tests and finite element stress analyses are performed on small size specimens modeling the welded joints between deck plate and vertical stiffener. In addition, fatigue strength curve is proposed for performing the fatigue durability evaluation for the portion repaired by the stop-hole method.
When steel tall frames are subjected to near-fault ground motions, collapse mechanism of a steel tall frame tends to be localized into single or lower several stories. This paper examines the feasibility of resolving this issue by adding base-hinged core trusses. Case studies are performed on the response of 20 story moment resisting frames designed in accordance with the Japanese design practice of high-rise buildings. In these studies, the response of the frames with core trusses to near-fault ground motions are examined by incremental dynamic analyses, wherein degradation due to local buckling at beam ends are taken into consideration. The results of the parametric analysis demonstrate that addition of relatively small amount of base-hinged core trusses leads to formation of global mechanism and significant reduction of response to near-fault ground motions.
The authors have carried out an investigation aimed at establishing an earthquake resistant design method for a Z-type NC braced frame. Our previous papers demonstrated the seismic performance of a single-story braced frame, and this paper clarifies the performance of a two-story braced frame from results of both shaking table tests on two-story braced frame specimens and of earthquake response analyses on actual-scale numerical models. It is concluded that elastic strain energy accumulation due to incremental story deformation angle can reduce absolute acceleration response. Furthermore, deformation behavior can be controlled by a brace arrangement and residual deformation after an earthquake can be predicted accurately.
In this research, the applicability of laser-arc hybrid welding to repairs on fatigue cracks from welds between deck plates and trough ribs is investigated. Firstly, in order to decide laser-arc hybrid welding conditions, which are laser output, welding speed and current, welding examinations are conducted. Next, fatigue tests are performed to evaluate the fatigue strength of repaired welds by using laser-arc hybrid welding. Their tests results show that the repair method is effective in improving fatigue strength, and is feasible for repairs on fatigue cracks in the welds.
In this paper, the improvement methods of plastic deformation capacity of pre-built-up H-shaped beam by submerged arc welding were investigated. First, a survey of improvement methods for the beam end connection of existing steel structure buildings was conducted. Next, the improvement effect about slit, boxing welding, backfill welding and web stiffener were investigated by the loading test. From test results, it becomes clear that the plastic deformation capacity of the beam increases by slit, backfill welding and web stiffener.