1. Assistant Professor, Tsinghua Univ., Beijing, China, 100084 (corresponding author).
2. Associate Professor, Dept. of Civil, Architectural, and Environmental Engineering, Univ. of Texas at Austin, Austin, TX 78712-0276.
3. Associate Director, Construction Industry Institute, Austin, TX 78759-5316.
4. Research Engineer, Construction Industry Institute, Austin, TX 78759-5316.