1. Ph.D. candidate, Dept. of Civil Engineering, The Johns Hopkins Univ., Baltimore, MD 21218-2682; formerly, Graduate Student, Dept. of Civil Engineering and Surveying, Univ. of Puerto Rico at Mayagüez, Mayagüez, PR 00681-9000.
2. Professor, Structures Dept., Facultad de Ciencias Exactas, Físicas y Naturales, National Univ. of Cordoba, P.O. Box 916, 5000 Cordoba, Argentina, and Researcher, CONICET, P.O. Box 916, 5000 Cordoba, Argentina (corresponding author).