1. Department of Civil Engineering and Engineering Mechanics, University of Arizona, P.O. Box 210072, Tucson, AZ 85721;
2. Department of Computer Science, North Carolina State University, P.O. Box 8206, Raleigh, NC 27606 e-mail:
3. Department of Civil Engineering and Engineering Mechanics, University of Arizona, P.O. Box 210072, Tucson, AZ 85721 e-mail: