1. Assistant Research Fellow, Institute of Industry Technology Guangzhou and Chinese Academy of Sciences, Guangzhou 511458, P.R. China.
2. Professor, Dept. of Mechanics and Civil Engineering, Jinan Univ., Guangzhou 510632, P.R. China; and Key Lab of Ministry of Education of Disasters Forecast and Control in Engineering, Guangzhou 510632, P.R. China (corresponding author).