1. Professor of Vibration Engineering, Dept. of Civil and Structural Engineering, Univ. of Sheffield, Sheffield S1 3JD, U.K. (corresponding author).
2. Research Associate, Dept. of Civil and Structural Engineering, Univ. of Sheffield, Sheffield S1 3JD, U.K.
3. Lecturer, Dept. of Civil and Structural Engineering, Univ. of Sheffield, Sheffield S1 3JD, U.K.