The identification of damping ratios in buildings is a well-known problem and appears to be of important and crucial interest in the safety and serviceability design. When compared to an estimation of the stiffness, i.e. natural frequency, and mass, the damping ratio is the most difficult quantity to determine. Many previous studies have examined the characteristics of damping ratios from ambient vibration, but the measurement time is roughly within 2 hours. In this paper, characteristics of damping ratios and natural frequencies of 4 story RC building were investigated using long-term ambient vibration. Free vibrations were obtained using random decrement technique, and damping ratios were evaluated by the envelop function, continuous wavelet transform, and logarithmic decrement. It was found that although the natural frequencies show little variations with time, the damping ratios show some variations with time and the largest variations found in the damping ratios obtained from the continuous wavelet transform. The damping ratios from the envelop function showed the smallest mean and standard deviation. And the probability distribution of damping ratios seems to follow the logarithmic normal distribution.

1. 서론
 2. RD법 및 감쇠율 산출 방법
  2.1 기본 원리
  2.2 RD법에 영향을 주는 인자
  2.3　감쇠율 산출 방법
 3. 계측 건물
 4. 해석 결과 및 고찰
  4.1 고유진동수
  4.2 감쇠율
 5. 결론
 References

• 김용철(동경공예대학교 건축학과 부교수, 공학박사, Tokyo Polytechnic University) | Kim, Yong Chul 교신저자
• 윤성원(서울과학기술대학교 건축학부 교수, 공학박사, Seoul National University of Science and Technology) | Yoon, Sung-Won