1. Assistant Professor, School of Civil Engineering, Tianjin Chengjian Univ., Tianjin 300384, China; formerly, Graduate Student, Dept. of Civil, Construction and Environmental Engineering, Iowa State Univ., Ames, IA 50010.
2. Wilkinson Chair Professor, Dept. of Civil, Construction and Environmental Engineering, Iowa State Univ., Ames, IA 50010 (corresponding author).