Dears,

i ask what's the formula to be used to calculate the wind moment on tank from API 650

thanks for advance

wind_pressure * area, but depending on what section of the Code you're talking about, there are different wind_pressures.

Richard,

thanks for your response.
we have a cylindrical tank h=15m and D=13m with conical roof 9.45°
After calculation with tank software i verified the wind moment: Mw using the three API formulas below.
I find a difference between our result with API calculation and tank output

API FORMULAS:
-p=0.86(V/190)2
-p=1.44(V/190)2
-p=0.00256Kz.Kzt.Kd.V2.I.G
wich forùula adopted by tank to calculate wind pressure?
what is the formula to calculate Mw?

First and most important, TANK only uses the "Imperial" equations and constants. Input and output are converted using the specified units filter.

Wind_Moment = ( 18 * velocity_factor * outside_diameter * height * height / 2 ) +
( wind_uplift * roof_area * outside_diameter / 2 )

Hello,Mr.Rchard

Wind_Moment = ( 18 * velocity_factor * outside_diameter * height / 2 ) +
( wind_uplift * roof_area * outside_diameter / 2 )
i think that 18 refer to english unit for mm fil is it 0.86 ? according to API
but (18 * velocity_factor * outside_diameter * height / 2 )dont give a unit of moment lbf.ft
or (0.86 * velocity_factor * outside_diameter * height / 2 )dont give a unit of moment N.m but give a N only that is force unit
because (0.86*velocity_factor): KPa=KN/m^2
and (outside_diameter * height / 2):m^2
it is necessery to multiply this equation by the height H(m)
and for wind uplift according to API it is 1.44(V/190)^2?
- in the output (solution module)it is writed that velocity factor equal to (V/190)^2 but it should to multiply this per a factor (Kz.Kzt.Kd.I.G)to obtain the result writed on solution module
finally the formula used to calculate wind moment on tank:
Mw=[(Kz.Kzt.Kd.I.G)*(0.86*1000*(V/190)^2*(OD*H^2)/2)]+[1.44*1000*(V/190)^2 * roof_area * OD / 2]
OD: outsid diameter
Kz:velocity pressure exposed coefficient
Kzt:factor
Kd: dirctonally factor
I: Inportance factor
G:gust factor
is it just?
thank you you very much for advance
best regards

From Section 5.11.1: wind pressure shall be taken from Section 5.2.1.k.

From Section 5.2.1.k: wind pressure shall be 18 * (V/120)^2 on vertical projected areas of cylindrical surfaces and 30 * (V/120)^2 uplift (note the limit set in 5.2.1.k.2).

I apologize for the equation mentioned above, I was typing too fast. The proper equation is:
Wind_Moment = ( 18 * velocity_factor * outside_diameter * height * height / 2 ) + ( wind_uplift * roof_area * outside_diameter / 2 )

As I said in my first post, the wind force or moment depends on what Section of the Code your referring to. The equation you site (Kz.Kzt.Kd.I.G....) is from Section 5.9 and is used for wind girder sizing.

Any verifications you attempt should be performed in Imperial units, I wouldn't trust the SI equations in the Code. Not only are there errors, but they use "soft conversions" - which is another way of saying they rounded to make the numbers look nice, but this means computer software yields different answers depending on which units you use. For example, the velocity factor (V/120)^2 versus (V/190)^2: this implies that 120 mph is equal to 190 km/h. In reality, 120 mph is 193.121 km/h. Maybe a small difference, maybe not - but don't expect TANK to yield the same results as your hand calcs if you use the SI equations. As stated above, TANK uses everything in Imperial units, then converts the input and output to the units you specify in the configuration.