5.11.4 Sliding Friction (Wind Force) & 5.11.2 Self-Anchored Tanks (Overturning Moment)

[MohdYaseen2010]

(A) For (5.11.4) Sliding Friction check, I put Fwind = (PWS * As-Vertical) + (PWR * Ar-Horizontal) where:
PWS (Design Wind Pressure on Shell) [see 5.2.1k.1)] = 0.89 kPa (V/190)^2.
As-Vertical (Vertical Projected Areas of Shell) = Shell Height * (D + 2 * tins-shell).
PWR (Design Wind Uplift Pressure on Roof) [see 5.2.1k (1 & 2))] = MIN(1.48 kPa (V/190)^2 , (1.6 * PF.4.1) ̶ Pi).
Ar-Horizontal (Horizontal Projected Areas of Roof) = π * (D/2)^2.
Am I correct or wrong?

(B) For (5.11.2) Self-Anchored Tanks, I found in existing calculation that the Mw (Overturning Moment about Shell-to-Bottom Joint from Horizontal + Vertical Wind Pressure) = MWR + MWS where
MWR (Moment Due to Wind Force on Roof) = (PWR * Ar-Horizontal * D/2).
MWS (Overturning Moment about Shell-to-Bottom Joint from Horizontal Wind Pressure) = (PWS * As-Vertical * (Shell Height / 2)).
In my mind this wrong as Overturning Moment (Mw ) is about Shell-to-Bottom Joint from Horizontal + Vertical Wind Pressure, so it should be concerned to SHELL ONLY (Roof should not be included) & therefore should be equal to MWS + (PWS * As-Horizontal * D/2) where (As-Horizontal) is Horizontal Projected Areas of Shell = π * (D/2)^2.
Am I correct or wrong?

Mohd Yaseen

 

[JStephen]

On the first item, I would not include the uplift on the roof in the calculated force.
On the second item, it should be PWR as the existing calculation shows.

 

[Geoff13]

For (b), look at Figure 5.27 as a freebody diagram, in particular the point the Code is calculating the moment around. The wind uplift on the roof adds to the overturning moment from the shell wind pressure.

 

[MohdYaseen2010]

Dear JStephen/Geoff13;

For (5.11.4) Sliding Friction check, As I understood from you, the Maximum Allowable Sliding Friction shall be:
Fwind = (PWS * As-Vertical)
is it the same value as stated in F.8.2 (a) Uplift from Design Wind Velocity on Tank?

Mohd Yaseen

 

[Geoff13]

In (a) I think you've figured out the forces trying to slide the tank, but you still need to figure out how much resistance the tank has against sliding.