Kensaku Kaneko

POSSIBLE FAILURE MECHANISM OF LOWER STORIES INDUCED BY SUBTRACTION OF UPPER STORIES IN EXISTING CONCRETE FRAME STRUCTURES

This paper discusses the seismic performance of concrete frame structures in which the upper stories are subtracted. Mid-to-high-rise buildings are assumed, which are designed in the current building standards law in Japan. A shear spring model with multi degree of freedom is employed. An eigenvalue analysis shows that approximately triangle shaped vibration mode is changed into quarter sinusoidal shape after the several mass are removed. An estimation method of the ductility factor at the bottom story within the framework of response spectrum method is proposed. Finally, the estimation method and nonlinear time history analyses show that the subtractions of the upper stories possibly deteriorate the seismic performance contrary to expectations.