1. Professor, Dept. of Civil Engineering, Key Laboratory of Structural Engineering and Vibration of China Education Ministry, Tsinghua Univ., Beijing 100084, China (corresponding author).
2. Ph.D. Candidate, Dept. of Civil Engineering, Key Laboratory of Structural Engineering and Vibration of China Education Ministry, Tsinghua Univ., Beijing 100084, China.
3. Engineer, China Electronics Engineering Design Institute, Beijing 100084, China.