Wind Load Calculations According to CP 3:Chapter V-2:1972
There are may code that are being used world wide to analyze strictures for wind action. CP 3: Chapter V is an old code used for calculate the wind loads on a structure. If we referred new codes and compared them with this code, it does not show much of difference. However, this code can not be used to analyse a structure for the dynamic actions. Wind induce accelerations and its limitations can not be found with this code. For general purpose, this code can be used.
Wind Pressure can be calculated from following equation.
P = CqA
Where C = Cpi -Cpe
q = Wind Pressure
A = Tributary Area
Wind Pressure is calculated considering the site wind speed.
q = kVz2
K is depends on the country. The value given in the code or other appropriate value can used.
We need to combine the wind pressure coefficients when loads are calculated. However, we can not always combine the wind pressure coefficient obtained for windward and lever sides. For example, when you are calculating wind pressure in a building, we have to consider the internal pressure.
If we plan to apply loading separately for windward and leaverd sides desperately, we calculate wind loading separately by combining each pressure coefficient with internal pressure coefficient.
Internal pressure coefficient may vary. Generally it has fix values. It could be positive or negative. Consider calculation of wind loading on windward side. Say external pressure coefficient is +0.7 and internal pressure coefficient -0.3 and +0.2 (for a building with negligible probability of occurring dominant openings in severe storm).
Then wind pressure coefficient will be as follows.
0.7 - (-0.3) = 1.0 or
0.7 - 0.2 = 0.7
Wind pressure can be calculated considering the both. Similarly for the other side pressure coefficient can be calculated.
Say levered pressure coefficient is -0.5
-0.5 - (-0.3 = -0.2
-0.5 - 0.2 = -0.7
Now we can apply loading after calculating pressure.
Pressure coefficient Windward 1.0
Pressure coefficient Leaved -0.2
Pressure coefficient Windward 0.7
Pressure coefficient Leaved -0.7
So we can calculate the wind pressure on each face of the structure.