1. Assistant Professor, Dept. of Civil and Environmental Engineering, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061-0105.
2. Nasser I. Al Rashid Chair in Civil Engineering, Univ. of Texas at Austin, Austin, TX 78712.
3. Graduate Research Assistant, Dept. of Civil and Environmental Engineering, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061-0105.