Equipment on Grade Anchorage - ASCE 7-16 Chapter 13 vs 15?

[AAHstruct]

A question has recently come up regarding the design of anchorage for transformers that are supported by foundations on-grade in California.

From ASCE 7-16, it's my understanding that the anchorage should be designed per Chapter 13 with the height in structure at point of attachment (z) set to 0, with "transformers" explicitly given in table 13.6-1.

Another SE has argued that Chapter 13 only applies for components attached to buildings or other structures, and that a transformer supported on a foundation directly on grade should be designed per Chapter 15, as an "Other self-supporting structure" per Table 15.4-2. His argument is that per Chapter 13, Section 13.1.1 Scope states "this chapter establishes minimum design criteria for nonstructural components that are permanently attached to structures and for their supports and attachments", and mentioned a SEAOC reference from his memory that he didn't have on hand. I tried to counter that the foundation is a structure, but he wasn't buying it.

I respect this person's opinion, so I can't dismiss it, but I can't find anything in the code or commentary that explicitly states that Chapter 13 can or can't be used for equipment supported on foundations on grade. Can anyone help me understand this one way or the other? I need to know, not just for this project, but for future designs as well.

Insights are greatly appreciated!

[As an aside, I didn't want to get into whether the transformer could be designed as a "Rigid Nonbuilding Structure" per Section 15.4.2 with this person, which gives a nearly identical seismic force as the minimum seismic design force for components in Section 13.3.1, depending on the Importance Factor.]

 

[dauwerda]

Check out section 13.1.1.

13.1.1 Scope. This chapter establishes minimum design criteria
for nonstructural components that are permanently attached to
structures and for their supports and attachments. [highlight #FCE94F]Where the
weight of a nonstructural component is greater than or equal to
25% of the effective seismic weight, W, of the structure as
defined in Section 12.7.2, the component shall be classified as a
nonbuilding structure and shall be designed in accordance with
Section 15.3.2.[/highlight]

As the weight of the "nonstructural component" (the transformer in this case) is equal to to 100% of the effective seismic weight, it should be designed per chapter 15.

 

[AAHstruct]

Thanks for the response, dauwerda, but I'm still not convinced that's the intent. If the transformer was supported on a platform structure and was 25% or greater of the seismic weight of the structure, then sure I'd agree, but there isn't a support structure like a platform or building in this case. Seems like if they had intended for all components supported on grade to be designed as nonbuilding structures per Chapter 15, they would have explicitly stated it, either in the spec or the commentary instead of wording it in one sentence in a way that could be misinterpreted, but I can't find anything one way or the other. They even allow for z=0 for components attached at or below the base of structures (is this any different than a component on grade?). I'd love to find something explicit, if anyone is aware of it.

Here's an article that's referenced in the commentary that also doesn't seem to explicitly state one way or the other:

http://www.skghoshassociates.com/sk_publication/Bachman,Dowty_reprint.pdf

 

[HTURKAK]

Mr dauwerda (Structural) has put the criteria for non-building structure or non-structural component. I just want to add , how to determine the applicable chapter for supporting structure vs supported item . The following snap from 2015 NEHRP Recommended
Seismic Provisions: Design Examples FEMA P-1051/July 2016 which is free document . The link is,

https://www.fema.gov/media-library-...c7a1d1a3b864648554198526d671f/FEMA_P-1051.pdf

There is worked example for elevated transformer at:

https://www.fema.gov/media-library-data/20130726-1601-20490-9357/fema451.pdf

 

[HTURKAK]

Dear AAHstruct (Structural),

I did not see your respond when i was writing my first respond which i could not see the reason with one hour time difference.
You did not define the type of transformer (dry ?) , and supporting system ( on wheels ? ).

If I were wearing your shoes, i would envelope the 13.3.1 and 15.4.2 .

Is the transformer anchored to foundation similar to this picture ?

 

[dauwerda]

Seems like if they had intended for all components supported on grade to be designed as nonbuilding structures per Chapter 15, they would have explicitly stated it, either in the spec or the commentary instead of wording it in one sentence in a way that could be misinterpreted, but I can't find anything one way or the other.

I disagree, ASCE 7 is written with consideration to structures - A transformer does not fall into this description. The only time the authors are worried about a transformer is when they are designing a structure that supports the transformer. A foundation for a transformer is not considered a structure and really falls out of the scope of ASCE 7 completely - that does not mean that the same principals wouldn't apply however.

The scope of chapter 13 that I highlighted above seems pretty explicit to me which chapter you should be using for the situation described - I really don't see how this could be misinterpreted, it is a very straight forward sentence included in the scope section of the chapter.

But as I mentioned above, the situation itself is really getting outside of the scope of ACE 7 (again, I'm not saying it can't be used or that the results would be wrong, just that it really isn't written with this situation in mind - which is why it isn't explicitly worded as you would like it to be). The document that is explicitly written for the situation that you have described is IEEE 693, IEEE Recommended Practice for Seismic Design of Substations.