1. Professor, Dept. of Civil Engineering, Beihang Univ., Xueyuan Rd. No. 37, Haidian District, Beijing 100191, China.
2. Student, Dept. of Civil Engineering, Beihang Univ., Xueyuan Rd. No. 37, Haidian District, Beijing 100191, China.
3. Professor, Dept. of Civil Engineering, Beihang Univ., Xueyuan Rd. No. 37, Haidian District, Beijing 100191, China (corresponding author).