Hanging Screw Conveyor in High Seismic Zone

[CWIGGPE]

I have been tasked with providing the hanger support and bracing design for a series of large screw conveyors to be mounted in the ceiling structure of a building in SDC "E". Rp=3, Ip=1.5. Given the weight of the conveyors, and the obvious high seismic forces, the lateral loads are quite large. The conveyors are approximately 40 feet long each, about 6000# fully loaded, and are rigidly mounted to eachother at right angles, with the entire conveyor system hanging from ceiling steel I-beams.

I have been using ASCE7 Chap 13 Eq 13.3-1 for these designs in the past, with my Rp, Ip, and overstrength provided in the project specs, given above. I have been unable to find anything in ASCE7 that specifically calls out the hanging or bracing requirements for conveyors in SDC "E". I would think that X-bracing the hangers or any other concentric bracing would be prohibited, or at least penalized in the calcs. I'd also like to know if energy dissipating connections and specialty devices are required for conveyors like they are for large piping and other mechanicals in "E" zones.

I am also interested if you all think AISC 341 detailing would apply to the hangers. I searched the forum and there are a couple of similar posts, but didn't seem to result in much consensus on what the appropriate design standards are for large hanging equipment bracing and support in high seismic zones.

Any insight you can provide would be greatly appreciated.

CWIGG

 

[WARose]

I have been using ASCE7 Chap 13 Eq 13.3-1 for these designs in the past, with my Rp, Ip, and overstrength provided in the project specs, given above.

To me, this would fall under Chapter 15 (not 13) in ASCE 7-10. They have coefficients for "Steel ordinary concentrically braced
frame".....which (to my mind) is what this is. And you'd get an R-Value of 3.25.

I would think that X-bracing the hangers or any other concentric bracing would be prohibited, or at least penalized in the calcs.

There are height limitations for SDC E. (I.e. 35'.) See Table 15.4-1. in ASCE 7

I am also interested if you all think AISC 341 detailing would apply to the hangers.

Most definitely. See the "detailing requirements" column of that table.

 

[wannabeSE]

I disagree with using chapter 15. The conveyor weighs about 150 plf which is about the same as (2) 10" pipes with water. No special detailing (AISC 341) is required.

 

[WARose]

[blue](wannabeSE)[/blue]

I disagree with using chapter 15. The conveyor weighs about 150 plf which is about the same as (2) 10" pipes with water. No special detailing (AISC 341) is required.

Maybe there is a clause I am not thinking of here.....but even in situations where a non-structural component weighs more than 25% of the whole structure (i.e. the component and the supporting framing combined), ASCE 7 (in Chapter 15) kicks you into sections 15.3.2, 15.5, or Chapter 12 to get the R value for the supporting framing. These sections could potentially kick you into Table 15.4-1......which requires AISC 341 in certain cases.

 

[Sawbux]

I would stick with Chapter 13 for this. Table 13.6-1 has a listing for process conveyors. Footnotes have provisions that should be considered.

13.6.3 kicks you over to 13.6.11 which directs you elsewhere in Chapter 13.

 

[WARose]

I would stick with Chapter 13 for this. Table 13.6-1 has a listing for process conveyors. Footnotes have provisions that should be considered.

That would certainly be applicable for the machine itself and it's attachment (i.e. their seismic forces)......but after that, the conveyor ends and the supporting framing requirements begin (as per Chapter 15/12).