Author(s)

M. Midorikawa, T. Azuhata & T. Ishihara

Abstract

Previous studies have suggested that rocking vibration accompanied with uplift motion might reduce the seismic damage of buildings subjected to severe earthquake motions. In this paper, the three-dimensional seismic response of base-plate-yielding rocking systems with columns allowed to uplift is evaluated and compared with that of fixed-base systems by finite element numerical analyses. The study is carried out using ten-story, one-by-three bay steel frames of a base-plate-yielding rocking system. Base plates that yield due to tension of columns are installed at the base of each column. The earthquake ground motions are the JMA record of the 1995 Kobe Earthquake and a synthesized motion. The maximum input velocity is scaled to examine the structural response at 0.50 m/s. The main findings from this study are as follows 1) The base shear coefficients of the uplift model are reduced to 68% to 82% of the fixed-base model subjected to one-dimensional input motions in the horizontal direction and to 59% to 76% of the fixed-base model subjected to two-/three-dimensional input motions. 2) The horizontal roof displacements of the uplift model almost increase relative to the fixed-base model. The ratio of the uplift to fixed-base models is from 0.89 to 1.25 in the case of one-dimensional input motions, and from 0.78 to 1.30 in the case of two-/three-dimensional input motions. 3) While the girders of the fixed-base model yield in bending at the second to eighth floors, those of the uplift model yield in bending only at the second and third floors. Keywords: seismic response reduction, rocking vibration, steel frame, column uplift, yielding base plate.

Keywords

seismic response reduction, rocking vibration, steel frame, column uplift, yielding base plate.