Wind Load Calculations According to CP 3:Chapter V-2:1972
There are may code that are being used worldwide to analyze strictures for wind action. CP 3: Chapter V is an old code used to calculate the wind loads on a structure. If we referred to new codes and compared them with this code, it does not show much difference. However, this code can not be used to analyze a structure for 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 the 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 depends on the country. The value is given in the code or other appropriate value can be 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 to load separately for windward and leaverd sides desperately, we calculate wind loading separately by combining each pressure coefficient with the internal pressure coefficient.
The internal pressure coefficient may vary. Generally, it has fix values. It could be positive or negative. Consider the calculation of wind loading on the 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 a severe storm).
Then the 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 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.
Case 01
Pressure coefficient Windward 1.0
Pressure coefficient Leaved -0.2
Case 02
Pressure coefficient Windward 0.7
Pressure coefficient Leaved -0.7
So we can calculate the wind pressure on each face of the structure.