1. Professor, Dept. of Civil Engineering, Key Laboratory of Structural Engineering and Vibration of China Education Ministry, Tsinghua Univ., Beijing 100084, China.
2. Ph.D. Candidate, Dept. of Civil Engineering, Key Laboratory of Structural Engineering and Vibration of China Education Ministry, Tsinghua Univ., Beijing 100084, China (corresponding author).
3. Associate Professor, Dept. of Civil and Environmental Engineering, Louisiana State Univ., Baton Rouge, LA, 70803; presently, Adjunct Professor, School of Civil Engineering and Architecture, Changsha Univ. of Science and Technology, Changsha, China.
4. Formerly, Graduate Student, Dept. of Civil Engineering, Key Laboratory of Structural Engineering and Vibration of China Education Ministry, Tsinghua Univ., Beijing 100084, China.