wood framed 120'x60' secondary structure need help with lateral load compliance.

[Torres_Structural]

Hi everyone, I'm looking at getting a 120ftx60ft garage/storage space for my house (own a big lot), and i'm looking at getting pre-engineered trusses and doing traditional 2x6 stud framing for walls. I've done a of commercial projects, and this is my first big project out of wood without intermediate framing for latera. I was looking at the IRC lateral wall braces and they all max out at 60ft spacing between wall lines. Would the IRC wall bracing parameters work on this structure? It will be a non-living space. The wind loads are 115 mph (ult) and the county requires code compliance structural drawings. I'm planning on doing all design and drawings myself. The plan is to have continuous footings around the perimeter. The structure has a few doors and windows, but the biggest part is the garage door (along the 60ft length wall) which might take some of the sheathing away for the lateral support. Any suggestions or guides out there for these types of structures and the parameters to which we can design them for? i think a pole barn is close to what I'm trying to achieve but not quite the same as i have stud framed walls and sheathing.

 

[JAE]

The IRC is for one and two family dwellings so not applicable to your project.

Are you in an area that requires licensed engineers on it and are you licensed for this? Assume you are but you seem to be attempting to design something in which you don't have the experience or education to tackle. Just asking.

For a wood stud wall system, lateral design would be via wood shear walls typically - using end posts and hold downs where required. The NDS (National Design Standard for Wood Construction) is what is typically used via the applicable IBC code. The wind/seismic loads are derived from ASCE 7 and applied to the structure to get the resulting lateral and vertical loads. These get distributed across the roof diaphragm and into the supplied shear walls.

 

[Torres_Structural]

@Jae Thanks for the reply. We are located in a township that county building codes are applicable and this needs to be designed and seal by an engineer(I'm a commercial structural engineer). I've done some multi-family and used sheathed stud walls for lateral. I've got my wind loads and have used all factors to get my MWFRS wind loads and applied them to the structure and will use the roof diagram, as well as the pre-engineered trusses to transfer the loads. My confusion lied in the IRC limitations for bracing and max spacing that we can have braced walls.

 

[phamENG]

IRC is prescriptive - if it fits in all the little (infuriating) requirements, it's a sufficiently reliable structure. Engineered designs throws off those shackles. There is some prescriptive nature to diaphragm and shear wall design, but a lot less. There are some aspect ratio limits and the assemblies have to match the tables or you're venturing into "alternative" design methods that aren't really a great idea unless you plan to build and test them destructively yourself.

So yes, the NDS is needed, but more specifically the Special Design Provisions for Wind and Seismic (SDPWS). This is where you'll find your diaphragm assemblies and capacities and shear wall assemblies and capacities. Deflection/drift is going to be important. Also, don't use the trusses to transfer the loads unless you have to. Stick to the diaphragm. It'll be a lot easier and less mistakes for the wood truss designers to make. There are some really good ones out there, but there are plenty that barely know how to read a drawing. I try to keep them as simple as possible whenever I can.

I'd also recommend reaching out to a colleague with the appropriate experience in your area to provide some guidance and give you a design review.

 

[Eng16080]

Although it's just a rectangle, for a structure of this size, there are a lot of things that you need to be aware of. I agree with the comment above that you should have an engineer experienced with wood review your design.

Following are a few comments based on a similar design that I recently completed:
[ol ]
[li]As noted above, this is likely well outside the limits of the IRC code. You'll need to design per the NDS code and SDPWS for wood diaphragm design and shear wall design.[/li]
[li]To transfer roof diaphragm forces from the roof sheathing into the shear walls, I'd recommend full depth blocking between the roof trusses. This is detailed accordingly to transfer the shear force from the sheathing to the blocking and from the blocking to the wall top plate. If you're relying on the wall top plate to also function as a diaphragm chord, then this force transfer will occur for wind load perp. to the wall as well as the normal case of parallel (perp. to gable end walls).[/li]
[li]Be sure to account for wind perp. to the walls in addition to parallel. At the gable end walls in particular, be sure that the top of the wall is adequately braced.[/li]
[li]With such a large truss span (60 ft.), the loads on the wall studs will be rather large, especially if you happen to be in a heavy snow region. For my project, due to the combination of tall walls, heavy snow loads, and moderate wind loads, 2x6 wall studs didn't work for the walls supporting the trusses. 2x8 studs were needed instead. [/li]
[li]At any large openings (garage doors) be sure to design for wind loads perp. to the wall in addition to the other loading cases. The wall framing/posts to either side of an opening should be continuous from foundation to the top of the wall (where they're braced). I find that this is often overlooked. Also, for these openings, the concentrated forces to either side may require the use of engineered lumber for the wall framing.[/li]
[/ol]

 

[JAE]

One other point to add to Eng16080's comments:

6. With a large building, with a long span diaphragm, you will most certainly have second order effects to consider. The diaphragm will deflect under lateral loads which induces leaning in the array of interior columns of the building. These columns, under axial load, will then produce P-Delta effects - essentially adding a bit more lateral load to the diaphragm, which, again, induces a bit more lean, etc. With more lateral load from the P-Delta effects, your shear walls will receive more lateral force than you calculate for the first order value.

If you don't know how to deal with this, again - get someone who does to help you. You stated you'd never tackled something like this before and practicing outside your experience, even with a PE license, isn't smiled upon by the boards of engineering.

 

[DoubleStud]

120x60 is pretty big. Have you considered a prefab metal building?

 

[Torres_Structural]

Thanks everyone for the replies. I do plan on having a friend who does wood structures review whatever I end up designing. I have contemplated getting a pre-manuf building, but based on the location, and my access to labor, I was planning on saving a few dollars by doing the stick framed instead of frames. I think my biggest set back on designing this was not fully understanding the limitations of the IRC and how much it can be applied. I do have access and experience with the NDS and the SDPWS book.

I was hoping to get a better approach to what could be designed with conventional framing. I've been researching on the aspect of these "specialty" buildings that are usually just pre-engineered and frames are used. Again, thanks for all the input and info. I'd definitely be consulting with someone with more experience as this is definitely not traditional work I'm used to, and wont be able to tackle on my own.