1. College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000, P.R. China
2. Key Laboratory of Mechanics on Disaster and Environment in Western China, The Ministry of Education of China, Lanzhou University, Lanzhou, Gansu 730000, P.R. China
3. Key Laboratory of Stomatology of The State Ethnic Affairs Commission, Northwest Minzu University, Lanzhou, Gansu 730030, P.R. China