Dear Sirs,
I use the Intergraph TANK software to design API 650 storage tank.

Input Data
- Tank Shell Height = 29 m.

Results from the software
- Maximum Height of Unstiffened Shell ................ 22.087 m.
- Wind Girder - Transformed Section Method
Number of Intermediate Girders Reqd ................ 0

My Question
- The Maximum Height of Unstiffened Shell(22.087 m) less than Tank Shell Height(29 m),

but the Number of Intermediate Girders Reqd = 0 ?

Thanks in advance for your support.