Effect of Soil-Structure Interaction of Low- and Middle-Rise Buildings Based on Strong Motion Data

Abstract eng:
The Building Research Institute (BRI) of Japan is a national institute engaged in research and development in the fields of architecture, building engineering, and urban planning. The BRI operates the strong motion network that covers buildings in major cities across Japan, as part of its research activities. Eighty-five strong motion stations are currently in operation. The dynamic soil-structure interaction (SSI) is one of key issues, which remain to be fully discussed, on the seismic safety of building structures. The complicated SSI phenomena are likely to be affected by the factors such as building structures, foundation types and soil conditions. Therefore, an observation of the actual SSI phenomena is useful in investigating their effects on the seismic safety. From a view of contribution to the SSI study, sensors have been installed in one third of the buildings in the BRI strong motion network both in doors and on the ground. In order to investigate actual SSI effects, twelve buildings having sensors both in doors and on the ground were selected from among those in the BRI strong motion network. The buildings vary in the number of stories, foundation type and ground condition. Furthermore, five earthquakes including the 2011 Tohoku Earthquake were chosen for obtaining strong motion data to be analyzed. First, peak accelerations were examined in order to discuss the amplification level of the earthquake motions across the area from the ground to the building top. The peak accelerations at the building foundation were generally reduced compared with those on the ground, and then were amplified by the building structures. The peak accelerations at the building top were 2 to 5 times higher than that at the building foundation. Second, the dynamic characteristics of the swaying-building and building systems were minutely investigated. The natural period of the swaying-building system was longer than that of the building system in every case. A difference in natural period between the swaying-building and building systems was significant in the low-rise buildings. A difference in damping ratio between the swaying-building and building systems was also large in the low-rise buildings. An increase in natural period caused by the Tohoku Earthquake was observed in many of the middle-rise buildings. Finally, the seismic input loss was discussed using the Fourier spectrum ratios between acceleration data on the ground and at the building foundation. Although the spectrum ratios of all the cases decreased in the short period range, their shapes were different depending on the building. The paper tried to clarify variation in SSI effect considering their relevance to various parameters, such as the building properties, foundation type and ground condition. We need a further investigation in order to discuss the contribution of those parameters to the seismic response of buildings.

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