1. Associate 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. Student, Dept. of Civil Engineering, Tsinghua Univ., Beijing 100084, China.
3. Master Student, Dept. of Civil Engineering, Tsinghua Univ., Beijing 100084, China.
4. Assistant Professor, Dept. of Civil Engineering, Tsinghua Univ., Beijing 100084, China.