PCA Circular Concrete Tanks - Missing Data in Tables 1

[JoelTXCive]

PCA's Design of circular tanks contains many tables for ring tension, shear, and moments of circular tanks. The tables present coefficients based upon the tank height.

These tables are all based on a Parameter "H^2/(Dt)" (tank height squared divided by the tank diameter and wall thickness)

At some point over the years, they expanded their original tables with supplemental coefficients for larger values of H^2/(Dt).

The supplemental coefficients are not for the full height of the tank though. They only cover the bottom 25% of a tank's height.

Does anyone know why? I searched the design manual and cannot find any discussion.

See below examples of the tables...

Thank you in advance.

 

[ATSE]

Joel - I tried to configure (imagine) a non-prestressed concrete tank that had H^2 / Dt > 50. Hard to do.
For both the considerations of the combined shear + flexural demand at the base, and shrinkage, tall non-prestressed concrete tanks are uncommon, and I certainly would try to persuade you toward either steel or prestressed (DYK / DN) Type I tank.
Non-prestressed concrete tanks are ideal for squat aspect ratio clarifiers and digesters less than 50ft tall.

 

[JoelTXCive]

In Houston, we have storm & wastewater lift stations all over the place. (We are so flat, and we are barely above sea level)

These lift stations range in size greatly, but are often 6 feet to 10 feet in diameter and can be 30ft deep.

We can get higher H^2/DT values easy. If you have a 10ft diameter wet well that is 30ft deep and has 24" inch walls, that gives you an H2/Dt value of 45.

We use the caisson construction method, so super thick walls are also common. It helps sink the wells.

Here's a sample one...

 

[JedClampett]

I always assumed that for higher than .75H, the hoop stresses apply. The fixity of the bottom doesn't make a difference.

 

[OldDawgNewTricks]

At some point over the years, they expanded their original tables with supplemental coefficients for larger values of H^2/(Dt).

The supplemental coefficients are not for the full height of the tank though. They only cover the bottom 25% of a tank's height.

Does anyone know why? I searched the design manual and cannot find any discussion.

The tables weren't expanded over the years. The same tables of supplementary coefficients was included in the 1943 edition, but they also included the following footnote: "For points not shown in the supplementary tables, ring tension and moment may be determined approximately by sketching curves similar to those in the text." For larger values of H^2/Dt, the coefficients at the top of the tank don't vary much so it doesn't appear to be an issue.

 

[JoelTXCive]

Thanks OldDawg.

Would happen to have a PDF of the 1943 version? If so, would you be open to posting on here? I would love to see it and I can't find that version online anywhere. (the copyright has probably expired)

The footnote makes reference to curves in the text. Maybe they have a nomograph or graphical procedure?

Conceptually, I agree with JedClampett. On tall-skinny tanks (large H2/Dt value), the fixity at the bottom has less and less of an effect as you move upwards. At some height it just reverts to pure hoop tension.

What about vertical moments about the base from the lateral earth pressure? I guess that as you get further away from the base, those just turn into pure compression on the hoop?

Ps. That's interesting about the supplemental values being there from the beginning. I just assumed they were added since they were labeled supplemental.

 

[OldDawgNewTricks]

JoelTXCive, Hathi Trust Digital Library Link

 

[JoelTXCive]

OldDawg - Thank you so much for that link! I downloaded 1 page at a time and then re-assembled the full book! (Luckily it was only 36 sheets)

 

[CarlB]

A great place to search is EngTips
SlideruleEra downloaded and posted the 1943 version here:

https://www.eng-tips.com/viewthread.cfm?qid=424804

 

[ATSE]

For a tall cylinder, simple axisymmetric hoop stresses dominate the behavior, except at the base. I think Jed said the same. Apply moment coefficients for the lower wall height = Diameter to determine your vertical wall dowels, then use minimum vertical reinforcing above.
On the West Coast, my guess is 80% of the sewer and small storm drain wet well / lift stations are stacked precast hoop sections (no vertical connection, except sometimes at base section).