1. Associate Professor, Key Laboratory of Civil Engineering Safety and Durability of China Education Ministry, Dept. of Civil Engineering, Tsinghua Univ., Beijing 100084, China (corresponding author).
2. Graduate Student, Dept. of Civil Engineering, Tsinghua Tsinghua Univ., Beijing 100084, China.
3. Associate Professor, Graduate School of Engineering, Hokkaido Tsinghua Univ., Sapporo, Hokkaido 060-8628, Japan.