1. Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province, School of Mechanics and Engineering, Southwest Jiaotong Univ., Chengdu, 610031 CN
2. Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province, School of Mechanics and Engineering, Southwest Jiaotong Univ., Chengdu, 610031 CN (Corresponding author), e-mail: lix_cai@263.net
3. MTS System Corporation, Eden Prairie, MN, 55344 US.