1. School of Human Settlements and Civil Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China
2. State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China e-mail:
3. Department of Engineering Mechanics, Zhejiang University, Hangzhou, Zhejiang 310027, China
4. Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588