Yoshihiro Onishi

Consecutive vibration characteristics monitoring of high-rise steel building

This paper reported the continuous seismic observation for a super-high-rise steel building in Osaka basin, Japan. We observed 16 earthquake records including the Tohoku earthquake on March 11, 2011. The signal to noise ratio is sufficiently good for all records. We estimated natural period and impulse response from those seismograms, and showed slight frequency shift due to nonlinear effect. We used microtremor records to estimate the natural period and damping of the building. By stacking sufficiently long records, we can extract those building property from microtremor records. Finally, the analysis models of the steel building used in the structure design are demonstrated based on the observed results. stories for the penthouse, and four stories under the ground level (Fig. 1(b)). The structure is steel moment-resisting frame above ground and steelreinforced concrete frame with shear walls under the ground level. The building is supported by the direct foundations with diaphragm walls. The depth of the direct foundation is 18 m from the ground and the diaphragm walls reaches to 35 m from the soil surface. The predominant natural periods of the design model are 2.28 seconds and 2.30 seconds in NS and EW direction, respectively (see Table 2). The designed damping factor is 2%.

STUDY ON THE EFFECT OF DEFORMATION-CONTROL SYSTEMS AGAINST PULSE-LIKE GROUND MOTIONS

The objective of this paper is to analyze the effect of deformation control systems against pulse-like ground motions. In this paper, we carried out time history response analysis for the models of the equivalent SDOF system and the MDOF system equipped with hysteretic dampers, viscous dampers and stoppers. As a result, the following conclusions are obtained. 1) Against the maximal pulselike ground motion, it sometimes happens that the additional hysteretic dampers increase the maximum story drift angle. 2) In all the cases, the additional viscous dampers decrease the maximum story drift angle. 3) Equipped with stoppers, there is a possibility to control unreasonable deformation against maximal pulse-like ground motions.

DYNAMIC PROPERTIES OF SKY- SCRAPERS LOCATED ON OSAKA PLAINS BASED ON OBSERVATION RECORDS DURING SOUTH-EAST OFF KII-PENINSULA EARTHQUAKE SEPTEMBER 2004

The system identification of the dynamic properties such as natural periods and damping ratios of four skyscrapers located on Osaka plains was conducted based on the observation records during South-east off Kii-peninsula earthquake September 2004 (M7.4). We found the dynamic properties in the large amplitude portions of response waveforms to be longer in natural period for all buildings and larger in damping ratio for a few steel-buildings than those in the onset and/or the terminal portions of response waveforms. The greatest coefficients of variation of natural periods in duration of response seismic motions were 2 to 4 percents for steel-buildings and 8 percents for a reinforced-concrete building.