WIND LOADS IN A BUILDING.

Wind is the air in motion relative to the surface of the earth. Since vertical components of atmospheric motion are relatively small, specially near the surface of the earth, the term ‘wind’ denotes almost exclusively the horizontal wind. Wind pressure, therefore, acis horizontally on the exposed vertical surfaces of walls, columns etc, and inclined roof of the structure. Wind pressure or wind loading is expressed in terms of a basic pressure p which is an equivalcnt static pressure in the direction of flow of wind. The basic wind pressure p should be decided on the basis of local meteorological data and local conditions, such as characteristics and location of structure and characteristics and duration of wind flow. In absence of any other data, the following relationship may be obtained by the expression.

For structures of various plan shapes other than rectangular plan shape, the external pressures acting on the projected area in the plane perpendicular to the wind, should be the product of the basic pressure (p) given above and thc shape factors given in Table 1.4.

TABLE 1.4. PLAN SHAPE FACTORS

thereof, having due regard to the level of mean retarding surface and variation in wind pressure with height. In making calculations, due regard should be given to shape factor and internal air pressure.
 

The stability calculations of the building as a whole shall be done considering the combined effect, as well as separate effects of imposed loads and wind loads on vertical surfaces, roofs and any other part of the building above the general roof level.
 

Calculations shall be made for the effect of wind on the design of individual components of the building. Where, however, adequate stiffering is provided by walls, or floors and walls, calculations for the effecas of wind, except in regard to wind panels, roofs amd foundations, need not be made on:
 

(a) A building or part of a building of which the heigh h does not exceed twice the effective widths,

(b) a section adjoining two parts of an adequately stiffened building, if height of the section exceeds twice its width but the length of the section does not exeed four times its width, and

(c) a wing of such a building if it does not project more than twice its own width. 

In the case of sloped roofs, the wind pressure varies with the degree of slope. The slope of the roof towards the wind direction is known as the windward slope, while the slope to the other side of the wind direction is 

known as the leeward slope. For flat and pitched roofs, the wind pressures normal to the surface, due to wind blowing at right angles to the ridge, in terms of basic wind pressure(p) are given in Table 1.5.

 TABLE 1.5. WIND PRESSURE ON ROOFS (WIND NORMAL TO RIDGE)