1. Assistant Professor, Dept. of Civil Engineering, National Taipei Univ. of Technology, Taiwan; formerly, Research Associate, Engineering Dept., Univ. of Cambridge, Trumpington St., Cambridge CB2 1PZ, U.K.
2. Senior Lecturer, Engineering Dept., Univ. of Cambridge, Trumpington St., Cambridge CB2 1PZ, U.K. (corresponding author).
3. Professor, Engineering Dept., Univ. of Cambridge, Trumpington St., Cambridge CB2 1PZ, U.K.
4. Soletanche-Bachy, 92000 Nanterre BP 511, France.