Ultimate Response of Superstructure Supported by Spread Foundation During Strong Earthquakes
Shuji Tamura*, Amane Kuriki**, and Kohji Tokimatsu***
*Disaster Prevention Institute (DPRI), Kyoto University, Gokasho Uji, Kyoto 611-0011, Japan
**Graduate School, Kyoto University, Gokasho Uji, Kyoto 611-0011, Japan
***Tokyo Institute Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
Dynamic centrifuge tests were performed on soilstructure models to investigate the mechanism of the ultimate superstructure response during strong earthquakes. Two structure models, one each for a highrise building and a low-rise building, differed in height but had almost identical mass and natural frequency. The following conclusions were drawn: 1) Superstructure acceleration amplitudes tended to reach the limit, although ground surface acceleration amplitudes increased with increasing input motion for both structure models. 2)Maximumacceleration of the high-rise building’s superstructure was markedly less than that of the low-rise building but the ultimate overturning moment acting on the footing base in both cases was almost identical during strong earthquakes. Overturning moment depends not only on superstructure inertia but also on the height of the superstructure’s center of gravity. Maximum superstructure acceleration for the high-rise building model therefore became small. 3) The overturning moment limitation when rotation angles were large was caused by local soil failure under the footing edge because the overturning moment was less than ultimate value (=PB/2), P is the weight of the structure and B is the footing’s width, and the contact pressure of the footing edge reached its ultimate.
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