Author(s)

T. Azuhata, T. Ishihara & M. Midorikawa

Abstract

To reduce seismic damage of steel building structures, a rocking structural system which employs the yielding mechanism of base plates has been suggested by the authors. When weak base plates yield due to column tension during a strong earthquake ground motion, the columns uplift and enable the building structure to rock. The performance of the suggested system for earthquake response reduction has previously been successfully demonstrated by the use of shaking table tests on a three story half scale braced frame. However, these tests also established that considerable vertical impulsive force occurs at the column bases when the uplifting columns touch down to their original position. The objective of this study is to investigate the influence of this impulsive force on earthquake response of real scale rocking structures. Earthquake response analyses are carried out on a steel model frame with yielding base plates. The frame has ten stories and one bay. The height and the width are 37.8 m and 7.5 m, respectively. The viscous damping is assumed to be proportional to the initial stiffness. The critical damping ratio of 2.0% is introduced to the first mode. The analysis results showed that vertical response acceleration on the frame is largely and instantly amplified by the impact effect when the uplifting column touches down. However, the impulsive vertical force does not damage the column, because it damps very quickly under the assumption of stiffness-proportional viscous damping. Keywords: rocking structural system, uplift, impulsive force, seismic damage reduction, yielding base plate, steel building structure.

Keywords

rocking structural system, uplift, impulsive force, seismic damage reduction, yielding base plate, steel building structure.