1. Kissling & Zbinden, 3608 Thun, Postfach 95, Bierigut-Strasse 11, Switzerland.
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of Alberta, Edmonton, Canada T6G 2G7.
3. Dept. of Civil and Environmental Engineering, Univ. of Alberta, Edmonton, Canada T6G 2G7.