Abstract
This paper presents the changes along passages of natural frequencies for a high-rise steel building based on microtremor measuring data. The building is 120m height, rectangular plan and it was completed in October 1998. Many data are simultaneously collected in two horizontal directions and torsional direction on each measuring floor since January 1999. It is clarified that natural frequencies at every direction or in each mode are decreasing gradually along the passages of time. Further more, natural frequencies measured on same date are different in each measuring time. Standard deviation and coefficient of variation are applied to consider the variation characteristics of natural frequencies on each measuring date.
