Comparison on Damping Ratios of an Earthquake-Proof Structure, a Seismic Strengthening Structure, and a Base Isolated Retrofit Structure

Abstract

Building No. 1, No. 2 and No. 3 at the Funabashi campus of Nihon University were built around the same time, and these buildings were built as 4-story earthquake-proof structures with the same structures and foundations1),2),3). After the structure, earthquake-proof reinforcement (Building No. 2) and seismic isolation retrofit (Building No. 3) were carried out to further improve their safety, and these are now an earthquake-proof structure (Building No. 1), a seismic strengthening structure (Building No. 2) and a base isolated retrofit structure (Building No. 3). To evaluate how the damping ratio of a building is affected by reinforcement and repair work on existing buildings, we measured and then compared the damping ratios of these three buildings. First, the velocities of these three buildings were determined based on microtremor observation and vibration experiment by human powered physical manipulation (i.e., people generated the vibration physically applying a force to the buildings) were measured by the velocity detectors on the ground, in the basement, on the second floor and fourth floor of each building. Then, the damping ratios were calculated by using the random decrement technique (RD Method). Damping ratios in each building have been compared, and differences of damping ratios by reinforcement work have been considered.