Conveyor System in SDC D - AISC 341?

[BS2]

I am designing a conveyor system for relatively light products (packages) in SDC D with the 2012 IBC & ASCE 7-10. This system consists of equipment and conveyor on top of cantilevered steel columns attached to a slab on grade. The system is <25% of the weight of the building.

2012 IBC Section 1613 refers to the ASCE 7-10 for seismic loads except for Ch. 14 which is overridden by the IBC.

After reviewing Chapters 13 & 15 of the ASCE 7-10, I it appears that I need to meet Section 13.6.11 which references conveyor systems. Section 13.6.11 sends you to Section 13.4, 13.6.3, 13.6.4, and 13.6.5 which sends you to Section 13.3.1 and Equation 13.3-1. Equation 13.3-1 refers to Table 13.6-1 where I find that "Manufacturing or process conveyors (nonpersonnel)" seems to fit with an Rp = 3.0. This all seems to fit well. Therefore, I believe that this should be treated as a piece of mechanical equipment. There is not mention of needing to detail this per AISC 341 and the overstrength factor is said to be N/A. Therefore, it appears that AISC 360 may be used for design.

Because the 2012 IBC overrides Ch. 14 of the ASCE 7-10, Section 2205 in the IBC applies to structural steel. Section 2205 says that for SDC D, E, or F, AISC 341 must be used except for as permitted in ASCE 7, Table 15.4-1. Table 15.4-1 does not seem to apply to mechanical equipment as it is talking about building systems and not cantilevered equipment legs. So, reading this section of code, it would appear that AISC 341 must be used for this equipment. However, the code is sufficiently vague and does not speak about my situation enough that I am not sure what must be used.

My question is: Do I need to design the steel columns in accordance with AISC 341? If so, can I use a reduced R value from Table 12.2-1 to get around this requirement?

If anyone has maneuvered through this situation and code section(s) and would be willing to give some advice, I would greatly appreciate it.

I apologize for the length, but I wanted to be complete.

Thanks!

 

[JAE]

AISC 341 has a user note that reads:

[blue]User Note: ASCE/SEI (Table 15.4-1) permits certain nonbuilding structures to be
designed in accordance with the Specification in lieu of the Provisions with an
appropriately reduced R factor.[/blue]

Would this be your out?

 

[JAE]

Schwandon,

You might also try this webinar from NCSEA that is coming up - might be just what you need to clarify this:

http://www.ncsea.com/calendar/2014/2/6/20140206_02062014/

 

[BS2]

Thanks for the response JAE! And for the link to the webinar! I might just have to check it out.

I read that note and I agree it seems to provide limited relief from using the Provisions. However, it seems like conveyor systems fall under the mechanical equipment category of Ch. 13, not Ch. 15. I can probably use Ch. 15 and use a reduced R-value. I am sure it will come with a healthy penalty. If required, I will design it with the AISC 341.

However, Ch. 13 seems to be quite separated from the other seismic chapters. It almost stands by itself save for Equation 13.3-1 as referenced by Ch. 15. In fact, in Section 13.3.1 it even states "Where nonstructural loads on nonstructural components exceed Fp, such loads shall govern the strength design, but the detailing requirements and limitations prescribed in this chapter shall apply." This leads me to believe that the detailing requirements come exclusively from Ch. 13. Also, are steel tube columns supporting a conveyor system considered structural steel? It seems like they are in a different category than the structural steel described in Ch. 12 and Ch. 15 for non-building structures.

Thanks again!

 

[wannabeSE]

First, decide whether chapter 13 or 15 applies. If your structure/equipment is in a gray area, some engineering judgment is required. Honestly, I doubt AISC 341 would ever be required for nonstructural-equipment supports and attachments using chapter 13 loads. If the equipment is substantial, you may be justified using the reduced loads in chapter 15 (with AISC 341 detailing). However, you need to make sure the equipment and connections can withstand the amplified drift using the Cd factor.

By the way, if you want to look toward the future, ASCE 7-10 supplement No.1 adds overstrength factors for everything in chapter 13. At first blush, I don't have anything nice to say about this change.

http://www.asce.org/uploadedFiles/sei/Books_and_Journals/ASCE 7-10 Supplement 1 Provisions.pdf

 

[SrVaro]

We have had this issue on several projects. We requested clarification from AISC and IBC about the infinite loop the codes have caused with their references. Within the request for clarification we clearly defined the conflicts and highlighted the relevant sections. Only to receive a simple reply of follow the code, no assistance at all. The latest revision has the user note as JAE pointed out, however, it does not eliminate the issue. In order to make sure we are compliant we have adopted a brute force method. We adjust the R value conservatively so that we no longer have to follow the detailing requirements and design the members/connections for higher forces. The procedure is clearly defined within our design criteria notes listed on our drawings as required by IBC. This approach has been "approved" by several building departments in various regions of the US, via that fact that we received our building permits. While there is a potential for a material cost increases, we felt this was the best approach to meet intent of the codes.

 

[BS2]

I think that the simplest option may be to use a reduced R value. If I use R=1.0, does that result in an elastic structural response under a design seismic event? And if so, then can I use an overstrength factor of 1.0?

Also, the client would like this system to be functional after a design seismic event; this requirement is not for life safety or because of hazardous materials - the client simply does not want their equipment down. If the system does stay elastic, then in this case, is an importance factor of 1.0 appropriate?

 

[SAIL3]

If the conveyor is not supported off the building itself and has it's own supprt stl off the slab on grade, then, I would not consider it a "component" and would tend to use chp15....the requirement that it still function after an earthquake is difficult to guarantee. Using a R=1 would increase the chances that it would still function after a seismic event but still is no guarantee.If R=1 is used then I would use an overstrength factor of 1. In any case, it looks like the importance facor should be equal to one.
There was an article addressing this in structure magazine under "Codes and Standards", July, 2008.

 

[SAIL3]

attached is the article referred to in previous post..