Force from nonstructural component - how far does it go?

[Nick6781]

Per the first sentence of ASCE7-10 ch.13 - " This chapter established minimum design criteria for nonstructural components that are permanently attached to structures and for their supports and attachments. "

For illustration purposes, let's say we have a one-story steel-braced building with a concrete diaphragm roof. There's a generator on the roof. The screenshot below shows this.

When I do the lateral design of the building, I understand that the generator weight should be included per 12.7.2 -3 total operating weight of permanent equipment.

When I design the attachment and support for the generator per chapter 13, do I need to check everything along the load path of Fp? Technically, the generator is "supported" by everything along the load path of Fp. Additionally, the effect of Fp may be different from the story shear. For instance, Fp has both a moment and a horizontal force effect on the braced frames, while originally, the frames may have been designed using a horizontal shear only.

However, it still feels redundant to me to check them again.

I must admit, I'm finding this aspect of the design process quite perplexing. I'm eager to hear your insights and suggestions on this matter.

Also, how should this be checked in a computer model? Create a separate load case for Fp and combine it with other gravity loads?

 

[Greenalleycat]

In our code the force ends at the connection though I think they're reviewing that
Practically, for something big like the generator, I would consider it as a separate load case where you follow the parts loads through the structure (G + Parts Load)
I would expect that the loads would quickly get below the main structural seismic loads anyway so stuff would be 'ok by inspection'

 

[HTURKAK]

Pls look to the remaining portion of the parag.

( 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. 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
defi ned 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. )

That is if Wp greater than 0.25 (WS + Wp ) , look to the Section 15.3.2.

He is like a man building a house, who dug deep and laid the foundation on the rock. And when the flood arose, the stream beat vehemently against that house, and could not shake it, for it was founded on the rock..

Luke 6:48

 

[human909]

Maybe it is just my ignorance of the codes and clauses referenced. But surely designing your structure to include all non negligible loads is pretty important and pretty much central to our job as structural engineers.

lAlmost all of the structures I design have significant permanent equipment loads. I also design plenty of retrofits adding additional equipment.

Lateral loads beyond their seismic mass is rarely an strength ULS for the items I deal with. But it is often serviceability from vibration.

I have had to design for the upset load of a hammer mill that undergoes catastrophic failure. The rotational inertia loads will tend to throw it across the room if no suitably restrained!

 

[bobbyboucher]