1. Lecturer, Dept. of Mathematics, Foshan Univ., Foshan, Guangdong 528000; and, Ph.D. Candidate, School of Civil Engineering and Architecture, Central South Univ., Changsha 410075, People’s Republic of China.
2. Professor, School of Civil Engineering and Architecture, Central South Univ., Changsha 410075, People’s Republic of China (corresponding author).