1. Doctoral Candidate, Dept. of Civil Engineering, Tsinghua Univ., Beijing 100084, China.
2. Associate Professor, Dept. of Civil Engineering, Tsinghua Univ., Beijing 100084, China (corresponding author).
3. Associate Professor, Griffith School of Engineering, Griffith Univ. Gold Coast Campus, Queensland 4222, Australia.
4. Professor, Dept. of Civil Engineering, Tsinghua Univ., Beijing 100084, China.