Actual conditions of terrain roughness evaluated from numerical data of structural dimensions in Tokyo

The terrain roughness in the 23 wards of Tbkyo cannot be easily evaluated because of a variety of structures with different dimensions. The authors have characterized the dty fi-om the viewpoint of terrain roughness, using the numerical data of dimensions of all structures in the 23 wards. The area of the 23 wards was divided into about 2,600 regions with a 500m mesh, and the terrain roughness of each region was analyzed. The results indicate that the regions are classified into the following three groups ; that is, (i) regions in which the ratio R_{f≥ 4} of the building area to the mesh area for the buildings with four stories or over is less than 20%, (Ü) regions in which 20% ≤ R_f≥4->40%, and (iii) regions in which &R _fge;4≥ 40%. In addition to the conventional homogeneous terrain roughness, resulting from low-rise buildings, the influence of buildings with four or more stories should be taken into consideration in the evaluation of the wind speed profile for design purpose.