1. a Department of Civil and Environmental Engineering , Hong Kong University of Science and Technology , Clear Water Bay, Kowloon, Hong Kong
2. b Department of Civil and Natural Resources Engineering , The University of Canterbury , Private Bag 4800, Christchurch, New Zealand E-mail:
3. c Department of Civil and Environmental Engineering , Hong Kong University of Science and Technology , Clear Water Bay, Kowloon, Hong Kong E-mail:
4. d Department of Civil and Environmental Engineering , Hong Kong University of Science and Technology , Clear Water Bay, Kowloon, Hong Kong E-mail: