A SIMPLIFIED PREDICTION METHOD FOR SEISMIC RESPONSES OF BUILDING FRAME STRUCTURES ALLOWED TO UPLIFT

Abstract eng:
Previous studies cleared that rocking behaviors can reduce seismic damages of some buildings. Based on this knowledge, some rocking structural systems which are allowed to uplift during earthquakes intentionally have been proposed as one of seismic energy dissipation systems. In this study, we propose a simplified prediction method for earthquake responses of such rocking structural systems. To predict earthquake responses of the rocking systems, we need to evaluate effects of higher modes. We consider there are two sources to generate higher modes in the rocking systems. When a building starts uplift, higher modes simultaneously occur due to vertical inertial effects in the superstructure. Therefore, a dynamic overturning moment of the rocking systems surpasses that estimated statically. We evaluate this effect by using solutions of a free vibration of the target structure. Initial velocity for the free vibration can be specified if a velocity response spectrum is provided and the fundamental natural period, which is elongated after uplifting is appropriately estimated. Also, higher modes occur due to high-frequency components of an input earthquake ground motion. If the high-frequency components of the input motion are relatively large, performance for earthquake response reduction of the rocking structural system may deteriorate. These higher modes excited by the high-frequency components can be evaluated by using the response spectrum, too. We predict maximum earthquake responses of the rocking structural systems by combining the solution of free vibrations and higher mode responses of the corresponding fixed base model.

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