1. Professor, School of Economics and Management, Beijing Jiaotong Univ., Siyuan East Building, Haidian District, Beijing 100044, China.
2. Lecturer, College of Architecture and Civil Engineering, Beijing Univ. of Technology, Jiangong East Building, Chaoyang District, Beijing 100124, China (corresponding author).
3. Senior Engineer, Construction Quality and Safety Supervision, Ministry of Housing and Urban-Rural Development of the P. R. China, No. 9 Sanlihe Rd., Haidian District, Beijing 100835, China.