1. Lecturer, Dept. of Civil Engineering, Univ. of Glasgow, Glasgow G12 8LT, UK.
2. Cormack Professor, Dept. of Civil Engineering, Univ. of Glasgow, Glasgow G12 8LT, UK.
3. Research Assistant, Dept. of Civil Engineering, Univ. of Glasgow, Glasgow G12 8LT, UK.
4. Research Engineer, Dept. of Civil and Environmental Engineering, Helsinki Univ. of Technology P.O. Box 2100, 02015 HUT, Espoo, Finland.
5. Lecturer, Ecole des Mines de Douai BP 838 59508 Douai Cedex, France.