Local topography factor for design wind speeds near and on the escarpment with gentle slope: Fid-Bau Portal

Local topography factor for design wind speeds near and on the escarpment with gentle slope

Wani, Abdul H. / Varma, Rajendra K. / Ahuja, Ashok K.

Structural designers refer to Standards on Wind Loads for basic wind speed at a particular location while designing buildings and other structures against wind. These values prescribed in the standards are for almost flat or non-undulated ground. However, if a structure is to be built on or near raised ground such as hills and escarpments, effect of local topography is considered in the form of one of the modification factors to arrive at the design wind speed. The value of such modification factor is again picked up by the designers from the relevant Standards on Wind Loads. However, the information available in such standards in general and in Indian Standard on Wind Loads in particular is found to be limited and inadequate for certain situations. An effort has, therefore, been made by the authors to carry out experimental studies to develop detailed information about local topography factor. A model of an escarpment with gentle slope, i.e., 15° is prepared and tested in a boundary-layer wind tunnel. Mean wind velocity profiles are measured at many locations near and on the escarpment. The value of modification factor for local topography is then estimated from the measured values of wind velocities at different locations. Values of local topography factor, thus, obtained experimentally are compared with those obtained following Indian Standard recommendations. Conclusions drawn from the study indicate that recommendations given in the Indian Standard on Wind Loads for local topography factor need to be updated for arriving at the correct values of design wind speeds for the design of buildings and other structures near and on the escarpments.