Tank, Vessel on foundation-Anchor, Concrete Design with Overstrength factor (ACI 318-14, ASCE 7-16) 2

[KOJUNGMO]

Tank, Vessel on foundation Anchor, Concrete Design with Overstrength factor (ACI 318-14, ASCE 7-16)

I believe that there are many previous post on this issue.
However, I would like to get other engineer's opinions.

Here in after I will use "ACI" for ACI 318-14, "ASCE" for ASCE 7-16.
To be clear, [Concrete] [Steel] will be noted.
Design condition considered as below :
Seismic design category D
Pre-installed type anchor bolt used.
Tank or Vessel supported on concrete pedestal or concrete foundation.

1. Regarding ASCE
1) ASCE Sec. 15.4.9.1
Anchor in concrete shall be designed by Chapter 17 of ACI.

2) ASCE Sec. 15.7.3 a.
2.1) Anchor bolt[STEEL] embedded in concrete shall be designed by Sec. 15.7.5
ASCE Sec. 15.7.5 special detailing requirements
(1) Anchor bolt(STEEL) shall have minimum 8*diameter gauge length.
(2) Anchor bolt(STEEL) shall be designed(sized) without overstrength factor.

2.2) Connections[STEEL & CONCRETE] shall be designed to develop Ωo(Overstrength Factor) * Design force or Actual required strength of the anchor in tension calculated by referece document
Let's only consider that Overstrength Factor to be used.

3) Notation
- Anchor Bolt[STEEL] means "Pre-installed Anchor bolt"
- Connections[STEEL] means "Base Plate" , "Anchor Chair Plates" and etc.
- Connections[CONCRETE] means "Concrete Pedestal" , "Concrete Foundation" and etc.


4) Summary as per ASCE 7-16, Section 15.7.3
- Anchor Bolt[STEEL] - it shall be designed(sized) by "not overstrength" factored seismic load.
- Connections[STEEL] = Base Plate, Anchor Chair Plates - it shall be designed by "overstrength" factored seismic load.
- Connections[CONCRETE in tension] = Strength(breakout, pullout, sideface blowout) - it shall be designed by "overstrength" factored seismic load.
- Connections[CONCRETE in shear] = Strength(breakout, pryout) - it shall be designed by "overstrength" factored seismic load.
- Connections[STEEL] = Anchor Reinforcement in concrete - it shall be designed by "overstrength" factored seismic load.
- The only element that shall be designed "without overstrength" factor is "Anchor Bolt[STEEL]"


Question 1) Do you(engineers) agreed with above conclusion?

2. Regarding ACI
1) ACI Section 17.2.3.4.3(tension) and 17.2.3.5.3(shear) require "shall satisfy "one" of options"
2) ACI Section 17.2.3.4.3 Tensile anchor
- Option a) - Same and more as per section 15.7.5 of ASCE 7-16
- Option d) - Overstrength factor
3) ACI Section 17.2.3.5.3 Shear anchor
- Option c) - Overstrength factor

4) ACI Section 17.2.3.4.3 Tensile anchor
With above conclusion regarding ASCE,
- Anchor Bolt[STEEL in tension] - only option a) shall be used.
- Connections[STEEL in tension] = Base plate, Anchor chair plates = only option d) shall be used.
- Connections[CONCRETE in tension] = Strength(breakout, pullout, sideface blowout) = only option d) shall be used.
- Connections[STEEL in tension] = Anchor Reinforcement in concrete = only option d) shall be used.


5) ACI Section 17.2.3.5.3 Shear anchor
With above conclusion regarding ASCE,
- Anchor Bolt[STEEL in shear] - there's no option? -> Only way is that shear shall not be occurred or overcomed.
- Connections[STEEL in shear] = Base plate, Anchor chair plates = only option c) shall be used.
- Connections[CONCRETE in shear] = Strength(breakout, pryout) = only option c) shall be used.
- Connections[STEEL in shear] = Anchor Reinforcement in concrete = only option c) shall be used.

Question 2) Tensile Anchor : With ASCE and ACI, it seems like the only possible way is "mixed design option" like above(Tension : Option a) and Option d)). Do you agreed with this?

Question 3) Shear Anchor : With ASCE and ACI, it seems like the only possible way is "Shear shall be not occured or overcomed by frction load from vertical load" like above. Do you agreed with this?

Thanks for any responses.

 

[HTURKAK]

"Shear shall be not occured or overcomed by frction load from vertical load"[/b] like above. Do you agreed with this?]

I respectfully disagree with this, your argument..

It is not necessary to design the anchors for shear if you can prove that the total design shear loads are transmitted through frictional resistance to the the concrete foundation. However, in case of design shear load exceeds the frictional resistance , the base plate will transfer the remaining shear to the anchors by bearing of the base plate against the anchors.

If you have a specific problem, pls provide more information to discuss the design of anchorage design..

 

[KOJUNGMO]

Thank you for your reply.
Firstly, I agree with you.
option a) in ACI Section 17.2.3.5.3 could be used.
Kindly ask you,
How could I determine the shear force that can be transmitted to the anchor based on the development of a ductile yield mechanism in the base plate
In other words, would you tell me how to determine whether the base plate is ducitle yield or not.
Is there any reference example for the calculation?
And what do you think about other questions?

 

[HTURKAK]

If you consider failure modes for concrete ; ( breakout, pullout, side blowout..) theses are brittle failure and shall be avoided to all cost to obtain a ductile design..


This is copy and paste from STE05121 = (A ductile anchorage design can be defined as one in which the yielding of the anchor (or the reinforcement or the attachment to which the anchor attaches) controls the failure of the anchorage system. This will result in large deflections, in redistribution of loads, and in absorption of energy before any sudden loss of capacity of the system resulting from a brittle failure of the concrete (ASCE Anchor Bolt Report).

Since your thread is for Tanks, Vessels or mech eq...IMO, the ductility shall be provided by YIELDING OF ANCHOR ROD.. or if this is not possible ( for the reason of post installed anchors etc..) the ductility shall be provided by yielding of attachments ( in this case base plate is also included )..

Does this post answer to your question ? If not, pls provide some specific data for your case ( tank, vessel geometry, the loads etc) to get more specific responds.


I will suggest you to look , and There are some worked examples for practicing engineers;

-ANCHORAGE DESIGN FOR PETROCHEMICAL FACILITIES (PREPARED BY Task Committee on Anchorage... ASCE )

-Process Industry Practices PIP STE05121 Anchor Bolt Design Guide

 

[KOJUNGMO]

I have looked into the STE05121 and ASCE anchorage design as well.
However, the documents do not show the case of seismic shear higher than friction force when ductility required(Seismic design category C and more).

So I’ve asked you how to determine when the shear shall be resisted by ductile yielding of base plate as you mentioned before.

It maybe because the seismic shear regulation changed since ACI 318-11.(There’s no shear ductile yield)

I could use engineer judgement for shear.
But I would like to know how other engineer deal with.

 

[bones206]

I believe the industry traditionally allows the tank to slide as long as the tension anchors are properly designed to be ductile and dissipate the rocking action energy in an earthquake. Here is an excepert from API 650:

No additional lateral anchorage is required for mechanically-anchored steel tanks designed in accordance with this Appendix even though small movements of approximately 1 inch are possible.

In my mind this makes sense, as the sliding energy is dissipated via sliding friction and probably also in anchor rod bending. If you have a stiff shear-resisting element (shear lug, for example), less energy will be dissipated and the shear-resisting element would need to be designed for a full elastic seismic force. If you were to design such and element, it would make sense to use the overstrength factor. However, I think the traditional approach is to design the anchors for axial ductility while allowing the base to slide without any additional engineered restraint.

 

[HTURKAK]

The quote is excerpt from API 650 E.7.6 SLIDING RESISTANCE .. This approach is OK for seismic design moreover,sliding will reduce the amount of force transferred into the tank. However, for wind loading , the tank shall be considered empty and base friction may not be enough to resist sliding and you may need to design the anchors for shear...


In this case,I want to understand for seismic shear, the sliding effect which shall be resisted by the tank, process column etc. I did not mention the ductile shear yielding of base plate ..

Consider some cases ;

i= The structural steel column = The ductility shall be provided by plastic hinge formation at the bottom of the column and ductile yield of anchor bars. In order to make sure this criteria will work , the attachments including base plate, concrete design for shear, pull out.. , Anchor Reinforcement in concrete is designed with overstrength factor.. That is, when plastic hinge developed at base of column and anchor rods yields , overstrength multiplied elements are still elastic..

ii= Process column = The anchors shall provide the ductility .. The attachments ( chairs,... ) shall be kept elastic ..

iii= Storage tanks = If mechanical anchor is provided, the ductility shall be provided by anchor rods and ANNULAR BASE PLATE.. The base plate shall extent such that plastic moment SHALL develop at cantilever portion..

Any process vessel or tank or structural steel column which is experiencing seismic shear greater than the base friction , the anchor rods shall be designed to resist to the remaining sliding force if shear lugs or other means are not provided..

My personnel opinion regarding the order of yielding for structural steel anchorage should be ; first yielding of anchor rods , second plastic hinge development at base of column, third, bending yield of base plate..

I hope this respond makes sense.. If you have further question,now the sleeping time at my time zone.. i may reply tomorrow morning..

Good Luck..

 

[KOJUNGMO]

Thank you for reply
It is helpful for me. API’s traditonal way must be acceptable.

I may misunderstood what you’re saying about the base plate. I thought that you mentioned about option a) of Section 17.2.3.5.3 on ACI 318-14.

I fully agreed with your reply.


As you know ACI changed anchor bolt shear ductility is not possible to be provided.


You can find out full document by googling
“anchor aweigh John F. Silva“

Therefore, ACI option a) restraint the shear force acting on Anchor Bolt by Base plate ductile yielding.
ACI option c) using overstregth factor in order to maintain the anchor bolt in elastic condtion.
But in this case ASCE strongly against like “do not use overstrength factor for anchor sizing”

The one left question is same as before.
Shear acting on Anchor bolt (not Tension)
A) Overstrength factored? -> ASCE not allow
B) Not overstrength factored? -> ACI allow only if the maximum anchor shear force have to be reverse calculated from Base plate ductile yield.

So I’d like to know how other engineer calculate the reverse engineered shear force in detail.
Or how to calculate the ductile yielding of base plate, simply 0.6Fy(AISC 360 J4.2)? or other conditons?

 

[HTURKAK]

I fully agree that anchor bolt shear ductility is not possible to be provided...


I do not know what is googling.. Let me express my thoughts =

- Only the anchor bolts in the compressed part of the base plate can be used to transfer shear force. That is, the anchorage bolts at compression side which do not experience tension and shear simultaneously..

- During seismic event, as per the ductile design criteria , the anchor bolts yield first and will elongate. If tension bolts will experience shear, will bend rather than resisting to shear ..

- For bolts experiencing tension and shear ( IMO, except seismic design ) The following formula is used in Eurozone ,

Fvsd /Fvrd + Ftrd/(1.4Ftrd) ≤ 1.0


The original thread was for Tank, Vessel on foundation-Anchor, still you did not provide the tank/ vessel details..

 

[KOJUNGMO]

Googling means searching by google.
Thanks for the formula used in EURO.
It’s the code(ASCE,ACI) issue.

 

[bones206]

Check this out:

https://www.onguardgroup.com/technical/

These guys have mastered the ductile anchor design concepts.

 

[IFRs]

You can find references to anchors in many codes. I think you should determine what code appiles to your situation, and ignore the rest. If yours is an API 650 tank, use API 650. Etc.

 

[KOJUNGMO]

Thank you for your attention.
I will look into it.

 

[KOJUNGMO]

The code used are ASCE 7-16 and ACI-318-14 as I posted in orgin.
If you have looked into the this code, then you could understand.

 

[IFRs]

Your question was about overstrength factor. Why are you using ACI and ASCE if this is an API 650 tank? Why complicate things? API covers anchor bolt strength. For the concrete anchorage details, certainly use ACI but for the anchor bolt design use API. Also, note that API 650 uses ASCE 7-10 now...

 

[KOJUNGMO]

As you understand,
The connection parts(including the anchor bolt, concrete pedestal, base plate and other attachment) can not be designed without considering each other condition, especially in seismic condition.
Only this way, engineer could provide safe design in seismic by either "ductility" or "elastic condition" or other way.

The connection part is not only mechanical engineering scope but also civil engineering scope.
If it can be determined by mechanical part only then only API could be used as you said.
When we design followed by ACI 318-08, ASCE 7-05, the shear ductility can be provided by Anchor bolt.
In that era, there's no complicated thing. as you said, only API -> Anchor bolt, Only ACI -> Concrete.
But, After observation of the Chile earthquake in 2010, we now know the shear ductility can not be provided by anchor bolt.
If you have look into the “Anchor Aweigh John F. Silva“, it would be helpful.

As you might know that ASCE 7-16 and ACI 318-14 are slightly changed from ASCE 7-10 and ACI 318-11 in the query field. So it's not the problem at all.

 

[HTURKAK]

How did you conclude that ? Will you please show us in ACI 318 the explicit statement ' ductile shear yield of base plate ' ?..
The failure mechanism of anchorage of storage tanks, vessels somehow different from structural steel anchorage.

API 650 uses working stress design ( WSD ) criteria and limits the Allowable Anchor Bolt Stress 0.8 X Fy (lbf/in.2) and Allowable Allowable Shell Stress at Anchor Attachment 25,000 (lbf/in.2) . That is, API 650 implicitly require the ductile yielding of anchor bolt while keeping shell and attachment stresses elastic.

 

[KOJUNGMO]

In original post, I’ve writen the section & clause in detail.
To sum up, ASCE Section 15.7.3 state “do not use overstregnth”. ACI Section 17.2.3.5.3 show the “three options for seismic shear”
First, maximum shear from the attchment’s ductile yield mechanism (only one lef)
Second, maximum shear from the attachment’s non-yielding (for special case like, sil bolts at wood)
Third, overstrength factor (ASCE does not allow)

 

[HTURKAK]

I am sorry if i disappoint you but i disagree with your conclusion of ( SHEAR FAILURE OF BASE PLATE ). However, IMO, bending failure and plastic hinge development at base plate can be acceptable.

If the seismic design shear loads exceeds the frictional resistance , you may provide shear lug and in the absence of shear lug,the base plate will transfer the remaining shear to the anchors by bearing of the base plate against the anchors.

The order of ductile failure mechanism should be,
1- Tension yield of anchors both sides with reversal of seismic load,
2- plastic hinge development at the base of column,
3- Bending yield of base plate,

The remaining shear will be essentially transmitted to the anchor bolts at compression side and due to small bending rigidity of the anchors, the bolts at tension side loaded by a shear force will bend, and develop of tension in anchor bolts.

I searched the web for your suggestion ;Anchor Aweigh John F. Silva and did need to read the article due to the hat of writer with post installed anchor company.

But i will suggest you to look the following doc. in order to get the concept which is a real paper.

https://people.fsv.cvut.cz/~wald/CESTRUCO/Texts_of_lessons/07-GB_Column_Bases.pdf

 

[bones206]

KOJUNGMO,

I think you are correctly pointing out that there is some gray area/conflict between ASCE 7 and ACI 318 regarding seismic anchor shear. I believe the intent of ASCE 7 15.7.3 was to prevent the use of overstrength factor method for anchor tension design, but they were not specific in their verbiage. The commentary sections C15.7.3 and C15.7.5 support this:

The changes made to Section 15.7.3(a) are intended to ensure that anchors and anchor attachments are designed such that the
anchor yields (stretches) before the anchor attachment to the structure fails.

It is also important that the bolt not be significantly oversized to ensure that the bolt stretches. The prohibition on using the load
combinations with overstrength of Section 12.4.3 is intended to accomplish this goal.

I think the code writers were focused on tension ductility, since that is the dominant energy absorption mechanism that they are trying to promote. However, I think they neglected to consider shear in anchors for the cases where friction alone cannot resist the total seismic shear.

In my opinion, shear resisting elements should remain elastic while the anchors provide axial ductility and energy absorption. If anchors are providing the shear resistance, then maybe this can be accomplished by necking the anchors above the cross-section that is resisting shear at the base level. This is in fact how the proprietary OnGuard anchor systems appear to be designed.