1. Department of Civil Engineering, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
2. Department of Civil Engineering, Carleton University, 1125-3432 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada.
3. Department of Civil, Geological and Mining Engineering, École Polytechnique de Montréal, C.P. 6079, succ. Centre-Ville, Montreal, Quebec H3C 3A7, Canada.