Machine Seismic Load?

[SteelPE]

I have a project where I am to design a roof penetration for a new machine that is to be installed inside of an existing structure. The machine is too tall for the existing building even though it is going to be placed into an 8' pit. The machine is a press that weighs 160kips. I have talked to the owner(who owns a few similar machines) about the foundation/pit requirements under the machine. All they basically need is a 16'x14' footing that is 28" thick (the thickness is just for the installation of their AB which require some special embedded sleeve).

In our office we are discussing the need for seismic support of the machine. Since my responsibility starts at the footing, I need to make sure the footing is capable of supporting the overturning moment created by the machine (I don't think I am going to have a problem but I still want to check it to make sure). We are trying to figure out which chapter of ASCE 7-05 is applicable to this type of work, Chapter 13 (Seismic Design Requirements For Nonstructural Components) or Chapter 15 (Seismic Design Requirements For Nonbuilding Structures).

Since the machine is self supporting, I say chapter 15 applies. My colleague contends that we should be using chapter 13 because we are providing support for the machine and chapter 13 specifically addresses equipment supports. This is probably just an exercise, but what are others opinions?

 

[briancpotter]

If it's sitting on it's own foundation, and largely independent of the rest of the structure, it seems like chapter 15 applies. Chapter 13 seems to be focused on components supported by the rest of the structure.

From 13.1.1:

"This chapter establishes minimum design criteria for nonstructural components that are permanently attached to structures and for their supports and attachments."




Brian C Potter, PE

http://simplesupports.wordpress.com

 

[SteelPE]

Brian,

That paragraph is what we are both referencing. He is saying that "for their supports and attachments" is what allows you to use this chapter (since we are attaching the machine to the foundation). I am saying that we are not attaching the machine to the structure other than at the foundation and therefore this chapter does not apply.

 

[briancpotter]

Hrm, didn't think I'd be having a grammar lesson this morning.

"their supports and attachments" is modifying "nonstructural components that are permanently attached to structures", not simply "nonstructural components" - ie, it's still talking about something that's part of a larger structure.

This is further reinforced later in the section, where it says

"Where the weight of a nonstructural component is greater than or equal to 25 percent 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."

If we mosey over to chapter 15.3, the heading is "NONBUILDING STRUCTURES SUPPORTED BY OTHER STRUCTURES", which this clearly isn't.

Both sections are frustratingly vague (and the commentary is no help), but this seems like the most reasonable interpretation.

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[aggman]

I don't know the rigidity of your press, but I would likely say that this meets 15.4.2 (Rigid Nonbuilding Structures). Chapter 13 only applies to components mounted and supported by building type structures where the supporting frame is not specifically designed to carry the component. (Like a storage cabinet can be anchored to the floor in a building and that anchorage must be able to withstand seismic forces. This portion is where Ch 13 comes into play.) Since your press is on it's own independent foundation it is controlled by ch 15 and likely by section 15.4.2.

 

[wannabeSE]

SteelPE,

I would lean toward chapter 13, but I understand your concerns. Sometimes, it is best to set the code book requirements aside and find a safe solution. If you are not certain which chapter to use, quickly calculate a few seismic coefficients with reasonable assumptions using both chapters to envelope the solution. Then, use engineering judgment to select a coefficient that allows you to sleep at night.

I don't know if it will be particularly useful in this situation. But often times, NEHRP (FEMA 450 and 750) commentary provides better background than the ASCE 7 commentary.

 

[OldPaperMaker]

SteelPE,
I suggest that you go to the internet and find Structure magazine, July 2008 issue. There is a detailed article about what might be covered in these two chapters of ASCE7.

I hope that this helps.

 

[SAIL3]

I agree with aggman....odds are it is a rigid structure.....another way of looking at this would be what if one was starting a new design and the press machine was installed first and then the bldg was designed/built to enclose it.....one would not consider applying cpt 13 to this design.....

 

[oldrunner]

I don't know what seismic forces will be on your machine, but you may also want to check anything bolted on just to make sure that there won't be any damage to the machine itself. This could be cabinets as well as stuff inside the cabinet. Piping may also be checked - unless you don't mind the rattling around that happens during a seismic event.