Roof Dunnage Seismic Loads

[SteelPE]

I am in the process of designing some dunnage to support two 22k units o ntop of a large concrete building. I have successfully calculated the wind loads on the structure including the units. I am now trying to calculate the seismic loads. Code required is ASCE 7-10/IBC 2015. Do I use equation 13.3-1 of ASCE 7-10 combined with section 13.6 of ASCE 7-10 (seismic design requirements for nonstrucctural components) or do I stick with chapter 12?

 

[bones206]

Most likely Chapter 13. If the weight of the units is significant compared with the weight of the building (per ASCE 7-10, 13.1.1) that would kick you to Chapter 15, but I don't think that applies in your case.

 

[SteelPE]

I have no idea what the building weight, I would guess somewhere around 5,000 kips, maybe more. So the weight of the dunnage and units are tiny compared to the building.

For some reason, when I read chapter 13 I get the impression that this chapter would apply more to the unit itself than the dunnage.

 

[bones206]

I believe Chapter 13 provisions determine the seismic demand on the unit, which is then applied to the dunnage as your design seismic load. Check out example 18.6 in FEMA 1051. It's somewhat analogous.

 

[wannabeSE]

Chapter 13 includes the supports and attachments for non structural components. I’m not sure I understand “Dunnage” in this context. If it is supports for the equipment to transfer the load the building, then I would use chapter 13.

 

[SteelPE]

WannabeSe,

In this instance, dunnage is a steel frame that we are placing the unit on to transfer the weight to the building columns below. The frame is approximately 4'-0" off the roof, is designed to support a cat walk around the unit and is also designed to transfer the loads from the unit directly to the columns below.

 

[Hokie93]

wannbeSE and bones are correct; Chapter 13 applies to both non-structural components and their supports and attachment to the primary structure (see Section 13.1.1 of ASCE 7-10).