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Chimney subjected to wind pressure

Tall structures like tower, chimney, pillars, etc. are subjected due to wind pressers. They are subjected by mainly two forces first one is its self-weight and another is force due to wind. And due to these forces direct and bending stresses are developed in tall structures. Direct stresses are developed due to self-weight and bending stresses are developed due to wind pressures.
In above fig. 8 a circular chimney of external diameter ‘D’ and internal ‘d’ is subjected due to wind pressure of ‘p’. The wind pressure is applied on total height ‘H’ with external diameter ‘D’. Therefore projected area of wind pressure is height ‘H’ multiplied by width ‘D’.
Now, we know that resultant stress

First discuss about direct stress σ0 which is developed by self-weight of chimney.
We know that 

Where,
A = Base area;
W = Self-weight; 
W = Volume  X density of masonry of chimney;
Here volume is depends on shape of chimney,
Volume for uniform circular cross section 
= Base area X height

Where;
D = external diameter of chimney;
d = internal diameter of chimney;
H = height of chimney;

Volume for uniform rectangle cross section 
= Base area X height

Where;
B = external breadth of chimney;
D = external width of chimney;
b = internal breadth of chimney;
d = internal width of chimney;
H = height of chimney;

Volume for non-uniform cross section 
= Average cross sectional area X height

Now, discuss about bending stress σb which is developed by wind pressure.
We know that

Here,
P = Wind force;
P = Wind pressure X projected area;
Projected area:
Projected area is the area where wind strike to chimney. Therefore this area equals to external face where wind strike, multiplied by height of chimney. Wind pressure for rectangular shape chimney is greater than as compare to circular shape because of its circular shape. Therefore during calculation of wind force for rectangular shape simply
P = Wind pressure X projected area
But for circular shape only it multiplied by wind coefficient.
P = C X Wind pressure X projected area
Where,
C = wind coefficient;
e = eccentricity of wind pressure = h/2;
Wind pressure act at center of height of chimney.
Z = section modulus 

I = moment of inertia;
ymax = max centroidal distance = external dimension/2

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1 comments

  1. UnknownJuly 8, 2021 at 4:22 AM

    thanks a lot this information was soo useful i had problem with my assignment but now m soooo sorted thank yu

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