Wind Load Calculation as per IEC 60826

Some of the data given by Customer is

dynamic wind pressure (q0 ) = 53.13 Kg / m^2

Reliability level = 2   (Return period of design load=150 yrs)

Ground roughness = B

q0  = 53.13 Kg/m^2

      = 521.20 N/m^2

As per IEC 826,

q0  = 0.5 X 1.225 X Vr^2

Therefore Vr = 29.17 m/s.

This "Vr" is inclusive of ground roughness.

Again, High wind velocity Vr = Vm X ground roughness coefficient.

For terrain class B, ground roughness coefficient = 1.0

Therefore, Vm = 29.18 m/s. we call it high wind velocity.

Now this is wind speed for that particular location.

But the wind pressure will vary depending upon height. It depends upon Drag coefficient & Gust response factor.

Drag Coefficient will remain constant at all height but Gust response factor will vary depending upon height.

Hence gust is main factor which will change the pressure at that height.

Assume we have divided pole shaft in three parts to apply wind loads as per our standard test procedure.
Let pole height = 30m
Assuming Drag Coefficient = 1.2 ( Same as insulator )

01) WIND PRESSURE AT 10m ABOVE GROUND.

    At Pole ht = 10m
    Gust response factor = 1.92
    As per IEC 826,
    Final wind pressure    = pressure x Drag x Gust
                                    = 521.2 x 1.2 x 1.92
                                    = 1201 N/m^2
                                    = 122.5 kg/m^2

02) WIND PRESSURE AT 20m ABOVE GROUND.

    At Pole ht = 20m
    Gust response factor = 2.2
    As per IEC 826,
    Final wind pressure    = pressure x Drag x Gust
                                    = 521.2 x 1.2 x 2.2
                                    = 1376 N/m^2
                                    = 140 kg/m^2

03) WIND PRESSURE AT 30m ABOVE GROUND.

    At Pole ht = 30m
    Gust response factor = 2.3
    As per IEC 826,
    Final wind pressure    = pressure x Drag x Gust
                                    = 521.2 x 1.2 x 2.3
                                    = 1439 N/m^2
                                    = 147 kg/m^2

Hence this is maximum wind pressure is at height of 30m.

To do the design at higher side we can refer max pressure for the entire height & for economical design we can use different pressure at different height as described above.

 

Gust Response factor for Pole & Insulator
Height	Terrain cat
	A	B	C	D
10	1.70	1.92	2.55	3.30
20	1.85	2.20	2.82	3.65
30	1.96	2.30	2.98	3.85
40	2.07	2.40	3.12	4.15
50	2.13	2.48	3.24	4.30
60	2.20	2.55	3.34	4.50
70	2.26	2.63	3.46
80	2.31	2.69	3.58

 

I hope the above information will help you.