1. Research Assistant, Dept. of Civil Engineering, The Univ. of Texas at Austin, Austin, TX 78712-0275 (corresponding author).
2. Associate, Estruconsult, San José, Costa Rica.
3. Engineer, Englekirk & Sabol Consulting Structural Engineers, Inc., Los Angeles, CA 90018.
4. Professor, Dept. of Civil Engineering, The Univ. of Texas at Austin, Austin, TX 78712-0275.