trou33
Structural
- Jul 11, 2019
- 6
I'm designing foundations for large (tall) industrial tanks and I have two related topics that are not clear to me.
Using ASCE 7-16 for wind pressures, 29.4.2 gives criteria for when to consider tanks grouped, isolated, or when to interpolate the drag coefficient. However, there does not appear to be instruction for what to do when the H/D is greater than 4. In my case, some of the projected areas on the round tanks vary from 40'Hx9'Ø to 70'Hx12'Ø, so I'm exceeding the upper limit of H/D by varying amounts. Even though the criteria from section 29.4.2 is specific, I think judgement can be applied to Figure 29.4-1 easily enough, but does anyone have experience with a different approach?
The main topic that's not clear to me is how having a center to center spacing between 1.25D and 2D is supposed to factor into the linear interpolation for Cf. The drag coefficient, Cf is determined from Figures 29.4-1 -29.4-4, as directed by Equation 29.4-1, but none of these figures mention grouped affects. The title of Figure 29.4-6 would indicate there are grouped affects on Cf provided, but this is only for instances where the spacing is less than 1.25D, which does not apply to my condition. What recommendations would you have for this instance?
For reference:
29.4.2 Design Wind Loads: Circular Bins, Silos, and Tanks with h≤ 120 ft (h ≤36.5 m), D ≤120 ft (D ≤ 36.5 m), and 0.25 ≤ H ∕D ≤4. Grouped circular bins, silos, and tanks of similar size with center-to-center spacing greater than two diameters shall be treated as isolated structures. For spacings less than 1.25 diameters, the structures shall be treated as grouped and the wind pressure shall be determined from Section 29.4.2.4. For intermediate spacings, linear interpolation of the Cp (or Cf ) values shall be used.
Thank you for your input.
Make no little plans.
Using ASCE 7-16 for wind pressures, 29.4.2 gives criteria for when to consider tanks grouped, isolated, or when to interpolate the drag coefficient. However, there does not appear to be instruction for what to do when the H/D is greater than 4. In my case, some of the projected areas on the round tanks vary from 40'Hx9'Ø to 70'Hx12'Ø, so I'm exceeding the upper limit of H/D by varying amounts. Even though the criteria from section 29.4.2 is specific, I think judgement can be applied to Figure 29.4-1 easily enough, but does anyone have experience with a different approach?
The main topic that's not clear to me is how having a center to center spacing between 1.25D and 2D is supposed to factor into the linear interpolation for Cf. The drag coefficient, Cf is determined from Figures 29.4-1 -29.4-4, as directed by Equation 29.4-1, but none of these figures mention grouped affects. The title of Figure 29.4-6 would indicate there are grouped affects on Cf provided, but this is only for instances where the spacing is less than 1.25D, which does not apply to my condition. What recommendations would you have for this instance?
For reference:
29.4.2 Design Wind Loads: Circular Bins, Silos, and Tanks with h≤ 120 ft (h ≤36.5 m), D ≤120 ft (D ≤ 36.5 m), and 0.25 ≤ H ∕D ≤4. Grouped circular bins, silos, and tanks of similar size with center-to-center spacing greater than two diameters shall be treated as isolated structures. For spacings less than 1.25 diameters, the structures shall be treated as grouped and the wind pressure shall be determined from Section 29.4.2.4. For intermediate spacings, linear interpolation of the Cp (or Cf ) values shall be used.
Thank you for your input.
Make no little plans.
