1. Assistant Professor, Dept. of Civil Engineering, Technological Univ. of Panama, Panama City 20297, Panama.
2. Associate Professor, Dept. of Civil Engineering, Univ. of Puerto Rico at Mayaguez, P.O. Box 9000, Mayaguez, PR 00680 (corresponding author).
3. Associate Professor, Dept. of Civil, Construction, and Environmental Engineering, Iowa State Univ., Ames, IA 50010.