1. Research Assistant, Dept. of Civil Engineering, Univ. of Chile, Santiago, Chile.
2. Associate Professor, Dept. of Civil Engineering, Univ. of Chile, Santiago, Chile.
3. Professor, Dept. of Civil Engineering, Univ. of Chile, Santiago, Chile.
4. Professor, Zachry Dept. of Civil Engineering, Texas A&M Univ., College Station, TX 77843-3136 (corresponding author).