JLNJ
Structural
- Oct 26, 2006
- 1,986
I have a few questions for those of you who have dealt with large scale rack structures. I am particularly interested in the type which are framed with regular hot rolled sections and which are, themselves, buildings where the cladding is supported from the rack structure. Seismic Design Category B, non-coastal wind speeds.
Any insight as to pitfalls and things to look for would be appreciated. I will probably not be the rack EOR (as it will be a purchased item) but I will likely be the foundation EOR.
The documents put out by the Rack Manufacturers Institute seem to be geared toward racks like you see at Lowe's or Home Depot; however, the language in the documents indicate that the provisions are for any rack. Most of my questions revolve around the seismic provisions, since my rack would be for storing relatively heavy industrial raw materials.
The RMI documents allow for a cross-aisle R of 4 and down-aisle R of 6. This doesn't quite line up with the R values in ASCE 7, but OK. They have some of their own research (see the FEMA 460 document). The MH16.1 document calls for testing of the assemblies to evaluate connection rotational capacity and a few other things. I presume this is in lieu of using the AISC seismic detailing provisions for R > 3. Like I said, the documents are geared toward the proprietary rack assemblies, not "normal" hot rolled sections, so I see the reason for the testing. Am I reading it correctly that the documents allow R of 4 and 6 with NO testing and NO special detailing as long as Cs is taken as Sds/R? This is pretty simple. No period calculation. No AISC 341. Vertical seismic distribution is triangular (the k exponent = 1.0). Seismic separation need not be checked in SDC A, B, or C. The down-aisle product load can be taken as just 2/3 the total product load. If I don't have that right, please correct me.
I guess I'm a little concerned that some of the provisions are a too conservative for my non-Home Depot application. I'm in a advising role to the Owner and I don't want him sold short.
From reading the FEMA document, some of the provisions have to do with rack behavior witnessed in actual EQ-event-loaded racks. The pallets slip and slide and the stacked materials move in such a way to reduce the EQ effect. The materials in my case are in bins, not loose on pallets, and they won't be sloshing around much, if any. I'm not too sure about the 2/3 down-aisle seismic weight for my case, either.
While I understand that the RMI has a vested interested in being as liberal as possible for their rack design to keep their products cheap (read: competitive), I feel we are wandering from the "normal" rack realm. I would like to recommend to the Owner that the rack designer use ASCE 7, but ASCE 7 specifically allows the use of the RMI documents (with a few minor edits).
I would also be interested in hearing any unique challenges you have found that these racking buildings present. The racks in my case may have a width to height of 10:1, so that's a little unusual right there. The uplift forces will be the real deal. The foundation will be pretty massive.
Any insight as to pitfalls and things to look for would be appreciated. I will probably not be the rack EOR (as it will be a purchased item) but I will likely be the foundation EOR.
The documents put out by the Rack Manufacturers Institute seem to be geared toward racks like you see at Lowe's or Home Depot; however, the language in the documents indicate that the provisions are for any rack. Most of my questions revolve around the seismic provisions, since my rack would be for storing relatively heavy industrial raw materials.
The RMI documents allow for a cross-aisle R of 4 and down-aisle R of 6. This doesn't quite line up with the R values in ASCE 7, but OK. They have some of their own research (see the FEMA 460 document). The MH16.1 document calls for testing of the assemblies to evaluate connection rotational capacity and a few other things. I presume this is in lieu of using the AISC seismic detailing provisions for R > 3. Like I said, the documents are geared toward the proprietary rack assemblies, not "normal" hot rolled sections, so I see the reason for the testing. Am I reading it correctly that the documents allow R of 4 and 6 with NO testing and NO special detailing as long as Cs is taken as Sds/R? This is pretty simple. No period calculation. No AISC 341. Vertical seismic distribution is triangular (the k exponent = 1.0). Seismic separation need not be checked in SDC A, B, or C. The down-aisle product load can be taken as just 2/3 the total product load. If I don't have that right, please correct me.
I guess I'm a little concerned that some of the provisions are a too conservative for my non-Home Depot application. I'm in a advising role to the Owner and I don't want him sold short.
From reading the FEMA document, some of the provisions have to do with rack behavior witnessed in actual EQ-event-loaded racks. The pallets slip and slide and the stacked materials move in such a way to reduce the EQ effect. The materials in my case are in bins, not loose on pallets, and they won't be sloshing around much, if any. I'm not too sure about the 2/3 down-aisle seismic weight for my case, either.
While I understand that the RMI has a vested interested in being as liberal as possible for their rack design to keep their products cheap (read: competitive), I feel we are wandering from the "normal" rack realm. I would like to recommend to the Owner that the rack designer use ASCE 7, but ASCE 7 specifically allows the use of the RMI documents (with a few minor edits).
I would also be interested in hearing any unique challenges you have found that these racking buildings present. The racks in my case may have a width to height of 10:1, so that's a little unusual right there. The uplift forces will be the real deal. The foundation will be pretty massive.
