1. Professor, School of Civil Engineering, Shandong Univ., Jinan, Shandong Province 250061, China.
2. Research Assistant, School of Civil Engineering, Shandong Univ., Jinan, Shandong Province 250061, China.
3. Professor in Residence, School of Civil Engineering, Shandong Univ., Jinan, Shandong Province 250061, China; Associate Professor, Dept. of Civil and Environmental Engineering, California Polytechnic State Univ., San Luis Obispo, CA 93407 (corresponding author).