Wind Loads:
Wind velocities and the pressures caused by them vary from place to place and season to season. Those vary from gentle gales to strong cyclonic storms and can cause extensive damage to roofs, buildings or other structures, and thus have to be taken into account in the design of these structures. Wind velocities, etc. are assessed in meteorological observatories all over the country.
Basic wind Pressure
Wind pressures are expressed in terms of a basic pressure, p, which is an equivalent static pressure in direction of wind. The IS: 875 give maps of India showing basic maximum wind pressure.
The basic wind speed, Vb, is the wind speed measured in a 50 year return period, based on a gust velocity averaged over a short interval of time (3 seconds). As per IS : 875 (Part-III wind loads ) - 1987 six winds have been identified which correspond to the basic wind speed of 55, 50, 47, 44, 39 and 33 m/sec respectively.