The Amplitude Dependent Dynamic Characteristics of an Existing Building before and after Seismic Retrofit

Abstract

Amplitude dependency of the dynamic characteristics of an existing 9-story RC building with uni-axial eccentricity is addressed in the paper, based on the various kind of observations and vibration tests such as earthquake observation, micro tremor observation and forced vibration tests using various exiting forces like excitor machine, man induced load and the air gun type impactor, obtained these 35 years after its completion. The building was damaged during the 1978 Miyagi-ken Oki earthquake. During this earthquake, the maximum acceleration recorded at 9 floor exceeded 1G, 1040 cm/s, and the deflection angle of the building was of the order of 10 radian. The seismic retrofit work was performed from year 2000 to 2001, and it was the first large scaled reinforcement work. The vibration tests were performed before and after the retrofit work. After the retrofit work, the earthquake observation records were obtained for several earthquakes with different amplitude level. The dynamic characteristics of the building are comparatively discussed for three terms in the lifetime of the building, namely, Term-1, comprising the years after completion until before the Miyagi-ken Oki earthquake, this was the most severe earthquake for the building; Term-2, comprising the years after the Miyagi-ken Oki earthquake until before the retrofit work; and Term-3, after the retrofit work. The data obtained through the observations and tests make possible to discuss about the amplitude dependency of the dynamic characteristics of the building, the evaluation of the degree of damage before the retrofit work and the reinforcement effects after the retrofit. The damage detection technique is also addressed using the tests results before the retrofit work by comparing the vibration characteristics based on the structural model which explain well those after the completion. The remaining stiffness coefficients were calculated for each portion of the structural elements. Then, the seismic strengthening effect is discussed using the results after the retrofit. It was confirmed from the vibration tests that the torsional motion was reduced by the retrofit work. Through the damage evaluation of the building before the retrofit work, based on the system identification, it was found that the remaining stiffness coefficients of each portion of the structural

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Cite this paper

@inproceedings{MOTOSAKA2006TheAD, title={The Amplitude Dependent Dynamic Characteristics of an Existing Building before and after Seismic Retrofit}, author={Masato MOTOSAKA and Takeshi Sato and Yuu Yamamoto}, year={2006} }