Dear all,
Using Tank software, we analyzed an existing tank.
No data about the wind were available and wind velocity was set as 0.
Why in the output I found Mw=moment due to wind (hor-ver)press different from zero?
Which are the parameters that influence this Moment ?
How can I understand how the software calculate it?

Thanks in advance

I discovered something.
When I consider wind velocity 0 it works like it's not 0.
The Mw,moment due to wind (hor-ver)press is like 0.22*e^7.
If I consider wind velocity 0.0001 it works and Mw order is e^-14 so it's close to 0.
Is something that I missing? It seems to me that the software has a big bug and a great problem.
Please try to explain me what's wrong or what I'm missing.

Thanks in advance

I cannot guess what is that "0" for software, however I have the remark that under API 650 requirements you cannot consider wind of zero velocity. It is true that it is not forbidden, but technically you cannot say you considered zero velocity as 3-sec gust design wind speed.

Please see API 650, 5.2.1 Loads, point K
Wind (W): The design wind speed (V) shall be 190 km/hr (120 mph), the 3-sec gust design wind speed determined from ASCE 7, Figure 6-1, or the 3-sec gust design wind speed specified by the Purchaser (this specified wind speed shall be for a 3-sec gust based on a 2% annual probability of being exceeded [50-year mean recurrence interval]).

Best regards.

Just for information, the 12th edition of API 650 modified wind load as following"

k) Wind (W): The design wind speed (V) shall be either:
— the 3-sec gust design wind speed determined from ASCE 7-05 multiplied by √I, Figure 6-1;
or
— the 3-sec gust design wind speed determined from ASCE 7-10 for risk category specified by the Purchaser (Figure 26.5-1A, Figure 26.5-1B, or Figure 26.5-1C) multiplied by 0.78;
or
— the 3-sec gust design wind speed specified by the Purchaser, which shall be for a 3-sec gust based on a 2 % annual probability of being exceeded [50-year mean recurrence interval].

NOTE ASCE 7-10 wind velocities now have LRFD load factors and risk category (importance factors) built in, whereas API 650 uses the working stress. The 0.78 factor applied to the ASCE 7-10 wind speed provides a conversion to working stress levels.

Thank you marioq,

I guess you are right!

Thank you !!!