1. Dept. of Civil Engineering, Qingdao Univ. of Technology, Qingdao 266000, China.
2. Professor, Dept. of Civil Engineering, Qingdao Univ. of Technology, Qingdao 266000, China (corresponding author).
3. Professor, Dept. of Civil, Architectural and Environmental Engineering, Missouri Univ. of Science and Technology, Rolla, MO 65401.
4. Professor, Dept. of Civil Engineering, Qingdao Univ. of Technology, Qingdao 266000, China.