Structural Seismic Loads versus Equipment Seismic Loads

[jochav5280]

Good Day!

I design industrial buildings and have been asked whether or not our equipment suppliers need to report their ASCE 7-10 seismic loads to us for designing our structures.

My understanding is that they are to use ASCE's equipment seismic load section for designing the equipment itself, and we are to use ASCE's building seismic loads section to determine the seismic loads that our structure must resist. Additionally, the equipment seismic load section should be used also for the equipment supplier to determine the required anchorage forces to design their anchors for. As I understand it, all we need to know from the equipment supplier is the operating weight of their equipment and its location in our building. Please confirm my understanding or enlighten me.

Many thanks in advance!

jochav5280

 

[MotorCity]

If you ask any equipment supplier to provide the ASCE 7-10 seismic load for their equipment, you will be met with a "deer in headlights" look or a dial tone if it was a phone conversation.

Equipment suppliers should give you the operating weight of the equipment (and the center of gravity if you are lucky). Typically, that's all you will get and all you will need. You decide the remaining designing parameters (Ap, Rp, Ip, Sds, z/h, etc.)

 

[jochav5280]

Thanks MotorCity,

I still have a remaining question.

Namely, the equipment and its anchorage are to be designed to resist the seismic forces determined in Chapter 15 of ASCE 7-10, but the building supporting the equipment shall be designed for the seismic forces indicated in Chapter 12 of ASCE 7-10? There is some confusion over here as to whether or not this is correct. I believe this is the intent, as determining the seismic forces in the building are based on the mass distribution, whether you are using the Equivalent Lateral Force Method or Dynamic Modal Response Spectrum Method, so not considering the mass of the equipment in this calculation of Chapter 12 would throw the results off.

I'd appreciate any thoughts on this.

Thanks again,

jochav5280

 

[MotorCity]

That's correct. If you want to receive a more accurate seismic response from the analysis, you should include the weight of the equipment and its location in your model/analysis (especially if its a heavy piece of equipment), regardless of the type of analysis used. So if you have a beam that supports equipment and is also part of the lateral system, it needs to be designed to resist the seismic forces in the building and the seismic forces due to the equipment (applied simultaneously)

 

[JBONE1234]

A young Engineer here....I also have a question regarding Non-Structural Equipment Anchorage per ASCE 7-10 Ch. 13.

ASCE 7-10 Table 13.6-1 Footnote states that if equipment is located on isolators with an air gap greater than 1/4" the Fp force shall be doubled. If this does apply to our calculations are we still limited to the max Fp=1.6*Sds*Ip*Wp?

My current situation is a simple fan coil that only weighs 132 lbs, but with the doubling of the Fp force, and Over-strength factor of 2.5 for anchorage to concrete I'm getting loads to my anchors of over 2 kips!!

Any help will be appreciated!

P.S. This is my first post ever on this site... I come here all the time for answers and figured today would be a good day to join this community!

 

[JAE]

JBONE, welcome to the site! Hope you stay and benefit and contribute!

I haven't read the actual text but usually if there is a doubling of a value like Fp, the logic of the code, as I read it, is:

1. Determine calculated Fp.
2. Determine min/max Fp if they are stated.
3. Determine applicable Fp - either min., calculated, or max.
4. Double the applicable Fp if required.

It appears that the factor of 2 is for impact while the overstrength is to force the failure mechanism into a more elastic or plastic mode...two different things so they are no mutually exclusive and need to be added together.

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[JBONE1234]

JAE,

Thank you for your response! I've seen many of your responses throughout this site on many different topics that I've come here for help on, so your input is much appreciated!

So, from what I'm understanding... The doubling of the Fp also applies to the Max as well then? My calculated falls just slightly under the max, but once doubled exceeds the max....

These are some pretty large loads for a little fan coil.

 

[JAE]

Well, impact can be large (and uncertain....when in doubt make it stout) and you don't want the anchors to fail first.

To me I think the Fp max, if it is the controlling Fp, would get doubled to account for the additional force from impact.
Have you checked the commentary of ASCE 7 on this table?

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[jochav5280]

Hello JBONE1234,

Welcome! This has been a great resource for me.

As this was my original post, I saw your follow-up question and brought it to our senior engineers.

We're all in agreement that your original calculated Fp shall be within the max/min indicated in Section 13.3.1; after that, you can then double the resulting value when footnote-b applies.

Hope this helps,

jochav5280

 

[wannabeSE]

jochav
One additional thing concerning the equipment in the building. Keep an eye on the overturning forces for the equipment. The buildings beams and decks at the equipment need to be design for the Fp, equipment loads in chapter 13.

jbone,
The moral of the story is to specify vibration isolators with restraints in high seismic regions. Besides the ASCE 7 requirements, I think you will have a hard time finding an isolator that can take significant seismic loads without restraint either built into the isolator or with separate snubbers.

 

[jochav5280]

Thank you wannabeSE, that was my understanding as well.

Best regards,

jochav5280