1. Postdoctoral Research Fellow, Dept. of Construction Management, State Key Laboratory of Hydroscience and Engineering, Tsinghua Univ., Beijing 100084, PR China (corresponding author).or
2. Senior Lecturer, Cranfield School of Management, Cranfield, Bedford MK43 0AL, U.K.
3. Professor, Dept. of Construction Management, Tsinghua Univ., Beijing 100084, PR China.