1. Professor, Dept. of Construction Management, Tianjin Univ., Tianjin 300072, P.R. China.
2. Research Student, Dept. of Construction Management, Tianjin Univ., Tianjin 300072, P.R. China.
3. Research Student, Dept. of Construction Management, Tianjin Univ., Tianjin 300072, P.R. China (corresponding author).