1. Department of Civil Engineering, Nagaoka University of Technology, Nagaoka, Niigata 940-21, Japan
2. Division of Research and Development, Shinko Pantec Co. Ltd., 1-1-4 Murotani, Nishi-ku, Kobe 651-22, Japan
3. Department of Urban Engineering, the University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113, Japan