Walls and Pillars:

Wind Forces on Walls and Pillars

Several a time's masonry walls & chimney shafts are subjected to strong wind pressures. The weight of the walls or the chimney generates compressive stress in the base whereas the wind pressure introduces bending moment generating tensile & compressive stresses in the base.

Figure illustrated a masonry wall of height H and rectangular section B × D. the horizontal wind pressure of intensity 'p' is acting on the face of width B.

 Figure

Let the unit weight of material of the structure = γ

Self weight of the structure W = γ (BDH)

Area of cross-section at the base = B × D

Compressive stress because of self weight of the structure on its base,

f ₀  = γ (BDH ) / BD = γ H

Entire wind force on the vertical face = P = p × BH

Distance of centre of gravity of the wind force from the base = H/2

Bending moment, M  = PH/2 = p ×( BH ²/2)

Section modulus, Z = BD² /6

Bending stress, fb  =  Z = ± p ×( (BH ² )/2) × (6/BD²) = ± 3 p × (H²/D²)

Because to Bending Moment (BM), there shall be maximum tensile stress along edge 'ad' & maximum compressive stress along edge 'bc' of the base.

Resultant stress, f = f₀ - 3 p(H ²/ D²) along edge ad

                              f = f₀ + 3 p (H²/D²) along edge bc.