1. Professor, Vibration Engineering Section, College of Engineering, Mathematics, and Physical Sciences, Univ. of Exeter, Harrison Building, North Park Rd., Exeter EX4 4QF, U.K. (corresponding author).
2. School of Civil and Environmental Engineering, Nanyang Technological Univ., 50 Nanyang Ave., Singapore 639798.
3. Xodus Group, Kenneth Dibben House, Enterprise Rd., Southampton Science Park, Chilworth, Southampton SO16 7NS, U.K.
4. JTC Corporation, The JTC Summit, 8 Jurong Town Hall Rd., Singapore 609434.