Questions about PIP Storage Tank Foundation Design

[tmgczb]

Recently I have been reading PIP 03020. I will post some threads to clear my inquiries.
I am sorry that I posted this thread in "Civil General Discussion" Part. But I don't know how to delete that thread. Following are my questions.
1. Code mentioned, for load combination about hydrotest, soil bearing capacity is allowed to be increased by geotechnical engineer, will this be written in geotechnical report?
Or for more common wind load cases, will geotechnical report indicate increase for SBC?
2. Code mentioned that for uplift check, weight of product over foundation could be considered "in the case of seismic load". Does it mean for load cases without seismic load, product weight shall not be considered to resist uplift?
3. Code mentioned anchor bolts shall be placed inside outer face of hoop steel? Why is it required to be mentioned? I think there is enough distance between anchor bolts and hoop steel.
4. Code mentioned that in case depth of ring wall is smaller than its width, ring wall's behavior as an annular slab shall be considered, is there any proportion for beam design, that is, ratio of h to b, when this effect shall be considered?

 

[LittleInch]

tmgczb

First, you should never assume people are familiar with the documents you refer, so its always better to speel it out. The PIP set of documents, as far as aI can see, are essentially guidleines written by people associated with the University of Texas. I've never seen or used them so can't comment, but they are NOT "Codes" or Standards".

Hence taking small bits out and asking questions is not really a good idea without posting the whole section to which it refers.

1) Which "code"?? I imagine this is based on the fact that hydrotest is only a few days duration , whereas long term ground bearing load is what is calculated by the geo tech engineer. So a higher short term loading could be acceptable.

2) Sounds like it to me. Seismic is a law unto itself.

3) Don't know. Would need to see the wording and the diagram.

4) When h is less than b.

 

[HTURKAK]

Double posting is not allowed. Delete the other post or report to the admin.

5.6.2 Foundation Sizing
5.6.2.1 The width of the ringwall foundation should be determined on the
basis of the allowable soil-bearing pressure.
5.6.2.2 For load combinations including hydrotest, wind, or seismic loads,
the allowable soil-bearing pressure may be increased in accordance
with the recommendations of the geotechnical engineer.

Is this the clause ? First of all PIP s are industry practices they are not codes or standards. The allowable soil-bearing pressure increase for seismic 33% and for wind 20% was an old practice . But hydrotest loading condition , shall be recommended by the geotechnical engineer. I have designed some tanks with content having SG 1.6 , 2.0 .. which the service bearing stress higher than hyrotest.

2. Code mentioned that for uplift check, weight of product over foundation could be considered "in the case of seismic load". Does it mean for load cases without seismic load, product weight shall not be considered to resist uplift?

True.. product weight shall not be considered to resist uplift for the wind and internal pressure . Pls look Table 5.21b—Uplift Loads.

3. Code mentioned anchor bolts shall be placed inside outer face of hoop steel? Why is it required to be mentioned? I think there is enough distance between anchor bolts and hoop steel.

The relevant item is more than clear .. pls look ;
5.6.2.6
If uplift controls the design (anchored tank), sufficient
counterbalancing weight (the weight of the foundation, the weight of
soil over the foundation, and in the case of seismic loading, weight
of tank product over the foundation) should be provided to
completely resist the uplift. This design recommendation typically
results in most of the concrete ringwall width being located inside of
the tank shell. Anchor bolts should be placed with enough edge
distance to the outside of the ringwall to develop the strength of the
bolt. The anchor bolts should also be placed inside of the outer face
of hoop steel to facilitate construction.

4. Code mentioned that in case depth of ring wall is smaller than its width, ring wall's behavior as an annular slab shall be considered, is there any proportion for beam design, that is, ratio of h to b, when this effect shall be considered?

The relevant statement is clear ; If the ringwall foundation width is greater than its depth, the design should consider the foundation’s behavior as an annular slab with flexure in the radial direction. That is , if width is greater than its depth , model the ringwall as ring plate so radial and tangential effects considered . FEM is the way to go.

 

[tmgczb]

True.. product weight shall not be considered to resist uplift for the wind and internal pressure . Pls look Table 5.21b—Uplift Loads.

From Table 5.21a, SI, I cannot see that product weight is not considered.

 

[tmgczb]

Double posting is not allowed. Delete the other post or report to the admin.



Is this the clause ? First of all PIP s are industry practices they are not codes or standards. The allowable soil-bearing pressure increase for seismic 33% and for wind 20% was an old practice . But hydrotest loading condition , shall be recommended by the geotechnical engineer. I have designed some tanks with content having SG 1.6 , 2.0 .. which the service bearing stress higher than hyrotest.

Is there any code or guideline giving the increase proportion 33%/20%?

I understand for wind and seismic which are short term effect, soil bearing capacity is allowed to be increased.
Hydrotest is also short term effect. I just have few project experience, and I never read a geotechnical report telling this recommendation to increase SBC.
By the way, what is SG 1.6?

 

[HTURKAK]

From Table 5.21a, SI, I cannot see that product weight is not considered.

Look at the Net Uplift Formula, one cannot see the product weight since the product weight resists to uplift and you must consider that the tank could be empty. Copy and paste of the relevant snippet ;

 

[HTURKAK]

I understand for wind and seismic which are short term effect, soil bearing capacity is allowed to be increased.
Hydrotest is also short term effect. I just have few project experience, and I never read a geotechnical report telling this recommendation to increase SBC.
By the way, what is SG 1.6?

- Ask to geotek if bearing capacity is allowed to be increased for your specific project. ( I looked IBC 2006 and the relevant clause ;An increase of one-third is permitted when using the alternate load combinations in Section 1605.3.2 that include wind or earthquake loads.)
- SG 1.6 , specific gravity of liquid relative to the water density .( e.g . SG =1.84 for 94% Sulphuric acid )
I will advise you to make efforts to search and learn basics.

 

[tmgczb]

Look at the Net Uplift Formula, one cannot see the product weight since the product weight resists to uplift and you must consider that the tank could be empty. Copy and paste of the relevant snippet ;
How could we know that if product weight is considered in seismic case？

View attachment 2416

 

[tmgczb]

I will advise you to make efforts to search and learn basics.

I am pretty thankful.

 

[tmgczb]

Look at the Net Uplift Formula, one cannot see the product weight since the product weight resists to uplift and you must consider that the tank could be empty. Copy and paste of the relevant snippet ;


View attachment 2416

Table 5.21a gives formulas for uplift，Annex F.8 also gives 3 formulas.
What is the difference？

 

[HTURKAK]

How could we know that if product weight is considered in seismic case？

Mrw is the seismic moment and the seismic weight calculation includes content weight (see Annex E)

Table 5.21a gives formulas for uplift，Annex F.8 also gives 3 formulas.
What is the difference？

This is the clause (F.8.2) . The counterbalancing weight, in addition to the requirements in 5.12, shall be designed so that the resistance
to uplift at the bottom of the shell will be the greatest of the following.) . and this is additional requirement for foundation and not for anchors .In this case , the counterbalancing weight is the foundation weight.
IMO , this requirement should not be mandatory for raft -mat foundations since the raft can resist to perimeter uplift not only by own weight , but with bending stiffness also. Imagine that , in case of internal pressure , the tank will not fly like a balon but the bottom plate will tend be oval like a dish and uplift force will develop at perimeter anchors .

 

[tmgczb]

Mrw is the seismic moment and the seismic weight calculation includes content weight (see Annex E)


This is the clause (F.8.2 The counterbalancing weight, in addition to the requirements in 5.12, shall be designed so that the resistance
to uplift at the bottom of the shell will be the greatest of the following.) . and this is additional requirement for foundation and not for anchors .In this case , the counterbalancing weight is the foundation weight.
IMO , this requirement should not be mandatory for raft -mat foundations since the raft will resist to perimeter uplift with bending stiffness . Imagine that , in case of internal pressure , the tank will not fly like a balon but the bottom plate will tend be oval like a dish and uplift force will develop at perimeter anchors .

Yes, Mrw is seismic moment，but does W1 include weight of product?

 

[HTURKAK]

Yes, Mrw is seismic moment，but does W1 include weight of product?

No.. if the tank is anchored , the liquid content contribution to resistance to overturning is not considered . Pls look Appendix E ,
self-anchored tanks that use the inherent stability of the self-weight of the tank and the stored product to resist overturning forces.
E.6.2.1.1 Self-Anchored
For self-anchored tanks, a portion of the contents may be used to resist overturning. The anchorage provided is
dependent on the assumed width of a bottom annulus uplifted by the overturning moment. The resisting annulus may
be a portion of the tank bottom or a separate butt-welded annular ring. The overturning resisting force of the annulus
that lifts off the foundation shall be determined by Equation E.6.2.1.1-1 ...