Building No. 1, No. 2 and No. 3 at Nihon University were built in the almost same time, and those were made as the earthquake resistant constructions with four stories having the same structures and foundations. After construction, seismic strengthening, repair work for seismic isolation have been carried out, and those are now earthquake resistant construction, seismic strengthening structure and seismic isolation retrofit structure.
Velocities by microtremor observation and vibration experiment by human power were measured by using the velocity detectors, damping ratios were calculated by the random decrement technique, and differences of those damping ratios have been considered.
